GEOLOGY

Introduction. fiderable parts of the earth, as of the quarters, and topography, describing a particular province or district.

Geography may be conveniently divided into descriptive geography, or that part of the science which describes the form, limits, extent, and variety of surface of different countries, with the manners and customs of their inhabitants; and physical geography, or that part which teaches how to determine the situations of different places on the globe, and to lay down and delineate their positions for the information of others. Descriptive geography is the more popular and entertaining part of the subject. It is usually divided into ancient or classical geography, geography of the middle ages, and modern geography. The first branch of the subject considers the state of the earth so far as it was known or discovered at different periods, previous to the sixth century of the Christian era. The geography of the middle ages extends from the sixth to the fifteenth century, and modern geography from the fifteenth century to the present time. One of the most useful subdivisions of descriptive geography is that employed by Mr Pinkerton, who considers the geography of the several countries which he describes under four different heads. 1. Historical or progressive geography; in which he treats of the names, extent, original population, progressive geographical improvements, historical epochs and antiquities of the countries. 2. Political geography; under which he describes the religion and ecclesiastical institutions, government, laws, population, colonies, military force, revenue, and political relations. 3. Civil geography, comprehending manners and customs, language, literature, and the arts, education, cities and towns, principal edifices, roads, manufactures and commerce. And, 4. Natural geography, comprehending an account of the climate and seasons, face of the country, its soil, and state of agriculture, its rivers, lakes, mountains, and forests, and an enumeration of the natural productions and natural curiosities, which are usually found within each district*. Descriptive geography is sometimes styled political geography, while physical or general geography is called natural geography.

* Vid. Pinkerton's Geography, vol. 2. p. 3.

Among the other departments of this study we may mention sacred geography, or that which illustrates the sacred writings; and ecclesiastical geography, which describes the division of a country according to its church government, as into archbishops, bishops, &c.

Many writers of treatises or systems of geography give a detailed account of the historical events and commercial concerns of the several countries which they describe; but we consider this as unnecessary in a pure geographical work, as these departments belong rather to HISTORY and POLITICAL ECONOMY.

Some systematic writers on geography considering the term in a very comprehensive view, as including a description of the internal structure of the earth, as well as of its surface, have thought it necessary to enter into discussions respecting the original formation of the earth, and the minerals of which it is composed. How far they are right in this we shall not pretend to determine. In this work, these subjects will be treated of under the articles GEOLOGY and MINERALOGY.

Another subject relative to the affections of the earth, respects the physical and chemical changes that take place in its atmosphere. These properly belong to the

science of METEOROLOGY, and will be found under that Introduction.

We propose in this article to offer only an introductory outline of descriptive geography, as the several quarters of the globe, and their subdivisions into empires, kingdoms, and states, are described as particularly as is compatible with the limits of this work, under the several articles to which they belong in the general alphabet.

Our attention will be chiefly directed to physical geography, especially that part of it which describes the construction and use of globes, maps, and charts.

Physical geography is properly a branch of mixed mathematics, and its principles depend on geometry, and its kindred sciences, trigonometry and perspective. It is intimately connected with astronomy; and as these two sciences mutually illustrate each other, they are commonly taught at the same time. The physical changes that take place on the earth, as far as it is considered in its general character of an individual of the solar system, have been already explained under ASTRONOMY; and we shall have little here to add respecting them, except as they are modified by the situation of the observer on different parts of the earth's surface.

The principles and practice of physical geography, though strictly dependent on pure mathematics, may be, for the most part, explained in a popular way, so as to be understood by the generality of readers. This popular view of the subject we shall attempt in the present article, throwing every thing that is purely mathematical into the form of notes. It must be evident, however, that a reader who is conversant with mathematics will study physical geography to more advantage; and for this purpose, it will be sufficient to possess a moderate acquaintance with arithmetic, the elements of geometry, plane trigonometry, spherics, and perspective.

It is scarcely necessary to enlarge on the importance or utility of geography. It is one of those sciences, the knowledge of which is almost constantly required. Without an acquaintance with the geography of the countries that are the scenes of the actions which he relates, the historian must either be extremely concise, or his narration must be obscure and unintelligible. Geography affords the best illustration of history, and is equally necessary to the historian and his reader. To the traveller, under which denomination we may class the soldier, the sailor, the merchant, as well as those who travel for pleasure or curiosity, a previous knowledge of the countries, through which he is to pass, is always useful, and often indispensable. To the politician a comprehensive knowledge of geography is of the highest importance. If he is ignorant of the extent, form, boundaries, appearances, climate, &c. of the country with which he is at war, he will plan his hostile expeditions without effect, and will send his invading armies only to perish among the defiles of the enemy, or to meet a more inglorious and deplorable fate from the diseases of the climate.

Even, if we consider geography as a study of mere amusement and curiosity, it forms one of the most rational and interesting studies in which we can engage. Nothing can be more gratifying to the observer of mankind than to survey the manners and customs of various

History. rious nations, and to compare the relative state of civilization and improvement in countries widely remote from each other. The student of geography can sit in his closet, and accompany the adventurous traveller in his toilsome journey, through

"antres vast, and deserts wild,
Rough quarries, rocks, and hills, whose heads touch
heav'n!"

trace his progress over the boundless ocean, and draw from his narration a delightful fund of instruction and amusement, free (except in imagination) from those perils and hardships, which the writer had undergone.

At the end of this article, we shall offer a few remarks on the best method of teaching and learning geography. We must now take a brief view of the origin and progress of the science.

PART I. HISTORY AND PRESENT STATE OF GEOGRAPHY.

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History of geography. AN historical account of geography would be extremely interesting, as it would include, not only the progressive improvements of the science, considered as a branch of mixed mathematics, but an account of the successive discoveries of different parts of the earth that have been made by the more civilized communities. Such an account in detail, however, cannot be expected here; and we shall confine ourselves principally to a cursory view of the geographical discoveries of ancient and modern nations, reserving the progressive improvements of physical geography for those parts of the article to which they properly belong; as they would neither be so interesting nor so intelligible to a general reader, before he has been made acquainted with the principles of the science.

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Origin. As soon as mankind had formed themselves into societies, and begun to establish connexions with their neighbours, they would find it necessary to inform themselves of the position of the countries which bordered on their own; and very soon their curiosity would lead them to desire to form an acquaintance with the extent of the country in which they lived, and with many particulars respecting those which were remote from them. Thus, we see that scarcely had the sciences arisen among the Greeks, before their philosophers began to occupy themselves in geographical pursuits. We are told that Anaximander exhibited to his countrymen a plan of Greece and the neighbouring countries, and in this he was imitated by his countryman Hecateus of Miletus. Of the nature of these ancient plans or maps, and their progressive improvements, we shall speak more at large hereafter.

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Discoveries of the Phoenicians. Commerce, and the taste for adventures, which usually accompanies it, were doubtless among the first causes of geographical researches; but the Phoenicians are the earliest commercial people of whose discoveries we have any correct accounts. This people seem first to have investigated the coasts on the Mediterranean; and their navigators, extending their voyages beyond this sea, through the narrow channel which is now called the Straits of Gibraltar, entered the Atlantic ocean, and planted colonies in Iberia, a part of Spain, in the country of Tharshish, which is probably the modern Andalusia, and upon the western shores of Africa.

The learned Bochart, led by the analogy between the Phoenician tongue, and the oriental languages, has followed the tracks of the Phoenicians, both along the shores of the Mediterranean, and those of the Atlantic. These analogies are not always sure guides; but we can scarcely doubt that the city of Cadiz was a Phoenician colony, and it is not likely that this was the only one formed by that enterprising people.

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In the time of Solomon, Phoenician ships, employed by him, set sail from a port in the Red sea, called Ophir. Azion-Gaber, and passing from that sea through the straits of Babelmandel, carried on their commerce in the Indian ocean. The country of Ophir, to which they sailed, must have been at a considerable distance from the Red sea, as we are told that a voyage thither required three years. "The king (says the author of the first book of Kings) had a navy of Tharshish, with the navy of Hiram. Once in three years came the navy of Tharshish, bringing gold and silver, ivory, and apes and peacocks." Some have placed Ophir upon the coast of Africa, where the modern Sofala is situated: Others suppose it was a port in the island of Ceylon, or in the island of Sumatra, in which latter island there is still a place called Ophir. The gold dust and ivory brought from thence, seem to show that it was an African port. (See OPHIR.) M. Montucla supposes that the Phoenicians must even at this period have sailed round the continent of Africa, and that Ophir was some place on the Gold Coast (A).

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The Carthaginians, a Phoenician colony, imitated their predecessors. We know that they sailed into the Atlantic ocean, as far as the coast of Cornwall in England, whence they procured large quantities of tin. The same people made several attempts towards a complete survey of the western coast of Africa. Of these we have an account only of one expedition, that of Hanno, of which we have already given an account under the article AFRICA.

The Carthaginian navigators, if we may believe the recital of Diodorus Siculus, (lib. xv.) discovered a country situated in the Atlantic ocean, which furnished all the necessaries and conveniences of life. Some pretend that this country was America, but it is much more probable that it was some one of the Cape de Verd islands.

(A) The most celebrated writers who have supported the opinion, that Ophir was a port in Africa, are Montezquieu, Bruce, and d'Anville. Dr Prideaux and M. Gosselin again contend, that Ophir was a port in Arabia Felix, and the same with Sabæa or Sheba; and their opinions have lately been ably supported by Dr Vincent. See Vincent's Periplus of the Erythrean Sea, Part II.

islands. The Carthaginian senate, fearful that the relation of the sailors who had discovered such a country, might be the means of producing frequent emigrations, are said to have used every endeavour to stifle the memory of this expedition.

History speaks of several voyages undertaken by order of the kings of Egypt and of Persia, for the purpose of ascertaining the extent of Africa; and Herodotus relates that Pharaoh Necho, king of Egypt, employed some Phœnician navigators to sail along the coast of Africa, for the purpose of taking a more exact survey of it. See Africa.

M. Gosselin, who has considered the geography of the ancients in a very learned dissertation, maintains, that the different passages of ancient writers, who have always declared that the Phœnicians and the Greeks circumnavigated Africa, are not sufficient to prove the certainty of such a voyage. The passage in Herodotus has been discussed by him at considerable length, and he seems to have proved his relation to be nothing more than a romance, founded on the historical knowledge of the Egyptians. M. Gosselin, however, admits, that many ancient voyages took place from those countries in which geography had arrived at some perfection; and there are numerous arguments, proving that all the shores of the old continent had been sailed round. See Bailly's History of Astronomy, p. 307. edit. 1775.

Xerxes king of Persia, according to Herodotus, gave a similar commission about the year before Christ 480, to one of his satraps named Sataspes, who had been condemned to die. Sataspes entered the Atlantic ocean through the straits of Gibraltar, and bending his course towards the south, he coasted the continent of Africa, till he doubled a cape which was called Syloco, and which Riccioli considers as the same with the Cape of Good Hope. He is said to have continued his course to the south for some time, and then to have returned home, assigning as a reason for not proceeding further, that he had encountered a sea so full of herbage, that his passage had been completely obstructed. This reason appeared so ridiculous to Xerxes, that he ordered Sataspes to be crucified; but in this sentence he appears to have been rather too precipitate, as it is certain that in some latitudes there grows such a quantity of sea weed, that a vessel can scarcely make way through it; as in that part of the sea which lies between the Cape de Verd islands, the Canaries, and the coast of Africa, and is called by the Portuguese the sea of Saragossa. This shews that the relation of Sataspes may have been correct, as he might think it dangerous to attempt proceeding where he found himself so much entangled.

Herodotus has commemorated another marine expedition, undertaken by Scylax, by order of Darius the son of Hyrtaspes, and which probably took place about the year 422 B. C. Scylax embarked upon the river Indus, the course of which he followed to its mouth, from whence he sailed in the course of 30 months, either into the Arabian gulf, or the Red sea. This Scylax must not be confounded with a navigator of the same name, who, at a later period, made a voyage of investigation round the Red sea.

The conquests of Alexander the Great, if they added little to the happiness of mankind, had at least the advantage of throwing considerable light on the state of

geography at that time, as they afforded to the Greeks a more perfect knowledge of the river Indus, and of many parts of that vast country which derives its name from that river. Alexander does not seem to have penetrated to the Ganges, though his expedition led the way to the knowledge of that river; for soon after he went as far as Palibothra, a town situated on the river Indus, at its confluence with another river coming from the west. The followers of Alexander went down the Indus, as far as its opening into the Indian ocean, where they witnessed for the first time the phenomenon of the flux and reflux of the sea,—a phenomenon which excited in them great astonishment and terror. It was after this that Alexander detached, about the year 327 before Christ, two of his captains, Nearchus and Onesicritus, to investigate the coast of the Indian sea. Nearchus was ordered to return by the Red sea, and this he effected. Some fragments of his voyage have come down to us, and upon these has been formed an excellent work by Dr Vincent, entitled the "Periplus of the Erythrean Sea." This learned and valuable work is just completed by the publication of the Second Part, and affords much additional illustration of the geographical information and commercial enterprises of the ancients.

Onesicritus failed to the east, and if we may believe the account that is left of his voyage, he gave us the first exact information respecting the island of Ceylon. The measure given by Onesicritus, of the extent of the island which he investigated, viz. 7000 stadia, does not correspond to Ceylon, whether we consider the length or circumference of the island, (see CEYLON); and if we take it as the measure of the length, it more nearly corresponds to that of Sumatra. The relations of Nearchus and Onesicritus were extant in the time of Strabo, by whom the latter is said to exceed, in point of exaggeration, all the other historians of Alexander's expedition. At the same time, it must be acknowledged that there are many things related by Onesicritus, as quoted by Strabo, which sufficiently agree with what we know of India, and the productions of that country; for he speaks of the sugar cane, the cotton plant, the bamboo, &c.

The kings of Egypt who succeeded Alexander, took considerable interest in the progress of geography. The second of these kings, Ptolemy Philadelphus, about the year 280 before Christ, sent into India two ambassadors, Megasthenes and Daimachus, accompanied by the mathematician Dionysius. Megasthenes was sent to the king of Palibothra on the banks of the Ganges, and Daimachus to another Indian potentate. No account remains of the proceedings of Dionysius and Daimachus, but Megasthenes left an account of his journey, which is frequently quoted by Strabo, by whom it is considered as a mixture of real adventures and improbable exaggerations. These quotations of Strabo are certainly all that remain of the relation of Megasthenes; for the work published under the name of Megasthenes is a literary imposture, similar to the works of Berofus, Manetho and Ctesius.

In the reign of Ptolemy Lathyrus, about 115 years before Christ, other expeditions were undertaken, for the purpose of sailing round the continent of Africa.

Eudoxus and Cyclus having incurred the displeasure of Ptolemy, were sent on this voyage of discovery. They

History. They passed through the straits of Gibraltar, and circumnavigating Africa, returned by the Red sea. Lastly, in the reign of Ptolemy, furnished Alexander, about 90 years before Christ, Agatarchides, who had been the king's governor, was sent to take a complete survey of the Red sea, and wrote an account of his voyage, of which, however, there remain only a few extracts that are preserved by Photius, in his Bibliotheca, a work of ninth century.

17 Voyage of Pythias. The extension of commerce seems always to have been one of the principal objects of these voyages of discovery. It is not surprising, therefore, that the inhabitants of Marseille, which was early celebrated as a commercial city, appear among the ancient navigators who laboured to extend geographical knowledge. Two voyagers, Pythias and Euthymenes, undertook an expedition about 320 years before the Christian era. Euthymenes entered the Atlantic through the straits of Gibraltar, and turned towards the south, for the purpose of taking a survey of the coast of Africa. This is all that we know of his route; but Pythias steered northward, and after reconnoitring the coasts of Spain and Gaul, sailed round the island of Albion, and stretching still farther to the north, discovered an island which is believed to be the modern Iceland, or the Thule of the ancients, terrae ultima Thule. Perhaps, however, this was only one of the Ferro islands. Strabo, who appears to have been prejudiced against Pythias, treats his relation as fabulous, founding his opinion principally on the number of incredible circumstances that occur in his narration. Taking these circumstances, however, not according to their literal meaning, but in a figurative sense, they represent pretty well the state of the sea and sky in these countries which are so little favoured by nature. Pythias certainly seems to have been one of the first Greek navigators who entered the Baltic.

18 Ancient geographers. We have thus traced the progress of geographical discoveries to very nearly the period which we assigned as the limit of ancient geography; and shall now notice very briefly some of the principal scientific geographers of antiquity, whose names or writings have descended to posterity, and shall afterwards give a summary sketch of the knowledge which the ancients seem to have possessed of the habitable globe.

As geography is a branch of knowledge intimately connected with geometry and astronomy, it became an object of consideration with many of the ancient geometers and astronomers. We have already mentioned the names of Anaximander of Miletus, and his countryman Hecateus. Strabo also notices Democritus, Eudoxus of Cnidus, and Parmenides, to the last of whom he attributes the division of the earth into zones. These were followed by Eratosthenes, who lived about 240 years before the Christian era, and Hipparchus, who flourished about 80 years afterwards; Polybius, Geminus, and Posidonius. Eratosthenes wrote three books on geography, of which Strabo criticises some passages, though he frequently defends him against Hipparchus, who often affects an opposite opinion. Polybius wrote on geography as well as history, and as well as Geminus and Posidonius, is frequently quoted by Strabo. Polybius and Geminus argue with considerable acuteness for the possibility of the torrid zone being inhabited, a circumstance which was generally disbelieved

by the ancients; and they even adduce arguments which are very plausible, to prove that the climate of the countries under the equator is more temperate than that of those which are situated nearer the tropics.

We must not here omit a geographer and mathematician who lived about the time of Alexander the Great. This was Dicearchus of Mesina, the disciple of Theophrastus, who wrote a description of Greece in iambic verses, of which some fragments yet remain. What renders this work most remarkable is, that it contains the height of several mountains measured geometrically by Dicearchus. Thus, for instance, the height of Mount Cyllene is stated at 15 stadia, and that of Satabyce at about 14. Taking the stadium at 94½ toises, we have for the latter of these heights, at most 1400 toises, whereas many of the ancients assigned 300, 400, or even 500 stadia, as the height of some of their mountains.

With Dicearchus we may mention another geometer noticed by Plutarch in his life of Paulus Emilius; viz. Xenagoras, a disciple of Aristotle, who also employed himself in measuring mountains, and has assigned only 15 stadia, which is equal to about 1417 toises, as the height of Mount Olympus. In some of the later periods previous to the Christian era, we find the names of several geographers, as Artemidorus of Ephesus, who wrote a geographical work in eleven books, of which nothing remains; Scymnus of Chio, author of a description of the earth in iambic verses, which remains in a very mutilated state; Isidorus of Charax, who left a description of the Parthian empire, and Scylax of Caryades, author of a voyage round the Mediterranean sea, which is still extant.

The works of all these geographers, however, are 19 Strabo. trifling when compared with the geography of Strabo, a work in 16 books, which has come down to us entire. This is one of the most valuable works of antiquity, both from the spirit of discussion which runs through it, and the number of curious observations which the author has collected of different geographers and navigators who preceded him; and of whose works nothing remains except these extracts. Strabo lived in the reigns of Augustus and Tiberius, and was nearly contemporary with Pomponius Mela. This latter geographer wrote a work de situ orbis, which is little more Mela. than a bare summary, though it is valuable, as it gives us a sketch of what was known in his time respecting the state of the habitable globe. Pomponius Mela was followed by Julius Solenus, who has also treated of geography in his Polyhistor, a compilation which is sufficiently valuable from the number of curious observations which are there collected.

Of all the ancient geographers, posterity is most indebted to Ptolemy, who produced a work much more scientific than had ever been written on this science; a geography in eight books, which must ever be considered as one of the principal monuments of the labours of its author. In this work there appear, for the first time, an application of geometrical principles to the construction of maps; the different projections of the sphere, and a distribution of the several places on the earth, according to their latitudes and longitudes. This work must have been the result of a great many relations both historical and geographical, that had been collected by Ptolemy. It has passed through numerous editions.

Some time after Ptolemy lived, Dionysius the African, commonly called the Periegetic, from the title of a work that he composed in verse, containing a description of the world, which may be considered as one of the most correct systems of ancient geography, and was by Pliny proposed to himself as a pattern. This work was afterwards translated into Latin verses by Priscian, and by Avienus, the latter of whom also wrote a description of the maritime coasts in iambic verses, of which there remain about 700. Among the latest geographers of this period are reckoned Marcianus and Agathemares, of whom little is known, except that the latter was author of two books on geography.

The scattered works of most of these authors being difficult to procure, were collected by Hudson into one work, and published by him in four volumes octavo, in the years 1698, 1702, and 1712, under the title of Geographiae veteris scriptores Graeciae minores, together with a Latin translation and notes and dissertations on each by Dodwell. In this work we find the remains of Hanno, Scylax, Nearchus, Agatharchides, Arrian, Marcianus, Dicearchus, Isidore of Charax, Scymnus, Agathemeres, Dionysius the Periegetic, Artemidorus, Dionysius of Bisance, Avienus, Priscian, and some fragments of Strabo, of Plutarch, of Ptolemy, of Abulfeda, and of Ulug Beg. This is a most valuable collection, and as it had become extremely scarce, was a few years ago reprinted at Leipzig.

The above is a hasty sketch of the names and characters of most of the geographical writers within the period which we have assigned to the ancient history of the science. We shall have occasion to make some further observations on the more eminent of these geographers in a future part of this article.

With respect to the knowledge of the globe that was possessed by the ancients, there have been various opinions; some have considered them as very extensively acquainted with almost every part of it, not excepting some portion of America; while others have confined their geographical knowledge within very narrow limits. The following observations are chiefly drawn from M. Montucius, an eminent judge in every thing that relates to the history of the mathematical sciences.

As to the knowledge which the ancients possessed of the habitable globe, it is certain that they were well acquainted with Europe, or at least all that part of it which had been made subject to the Roman empire, as far as the banks of the Rhine and the Danube. They were tolerably well acquainted with Germany and Sarmatia. They had some knowledge of the Baltic sea, as a fleet had been sent by Augustus, which sailed as far as the peninsula then called the Cimbrian Chersonesus, the modern Jutland. The Baltic was at that time celebrated for the production of ambergris. They had acquired a knowledge of the island of Britain, from the expeditions of Julius Cæsar, and Claudius; but the northern parts of this island, and the whole of Ireland, were to them nations of rude, uncivilized savages. The boundary of their knowledge of Europe to the north, was the Thule of Pythias, or Iceland; at least if it is certain, as is the general opinion, that this island is the ultima Thule.

With respect to Asia, they seem to have surveyed the country as far towards the east as the river Ganges; and the immense extent of country compre-

hended between the Indus and the Ganges, was called by them India on this side the Ganges.

Further on towards the north of China, in the neighbourhood of the mountains where these rivers derive their source, they placed several nations of people, of whom they related the most ridiculous fables. Beyond these, still more towards the east, they placed the Seres, and upon the coast of the gulf, which is now the bay of Cochinchina, called by Ptolemy the Great Bay, were situated the Sine, so called by Ptolemy, though they are not mentioned by Strabo, Pomponius Mela, or Solinus. The Seres were probably the inhabitants of the northern parts of China, and the Sine, those of the southern parts of China, who very early occupied Cochinchina, Tonquin, &c. countries which in the sequel they have entirely subjugated. They maintained a commerce by land with the Seres, and their route is pointed out in one of Ptolemy's maps. Beyond the Seres, according to Strabo and Pomponius Mela, lay between the Oriental sea, though Ptolemy, for want of certain intelligence respecting that part of Asia, considers the point as undecided, and places there several unknown countries. The ancients carried this extremity of Asia much farther to the east than it is found to extend by modern geographers; for, according to them, the Seres and the Sine were situated about the longitude of 180°, while the meridian of Pekin, or about the middle of the Chinese empire, reaches no farther than to 134°, reckoning the longitude from the most distant of the Canary islands, as was done by Ptolemy. To the north of the Indus the ancient geographers placed the Scythians, and Hyperboreans (the Tartars and Samoides of more modern date) and some other nations to an indefinite extent, who were supposed to form on that side an insurmountable barrier, having behind them an ocean of ice, which was believed to communicate with the Caspian sea, though this was at least at the distance of 450 leagues.

The boundary of Asia, assigned by the ancients to the south, was the Indian ocean, and they were acquainted with its communication with the Red sea, by means of a strait, the figure of which is very ill expressed in their maps. This is also the case with the Persian gulf, with which they were acquainted, but which in the ancient maps has nearly the form of a rhombus, one side of which, towards the mouths of the Indus, was pretty well known to them, but the side next the mouths of the Ganges is very inaccurately delineated, being continued nearly in a straight line. It is even probable that the island which Ptolemy calls Taprobana, was only the peninsula of India very much disguised in the delineation.

The situation of this island of Taprobana, so celebrated among the ancients, is a problem in geography of the island that is yet unsolved. It is commonly supposed to be the modern island of Ceylon; but the dimensions of it as laid down by ancient geographers, render this supposition doubtful, and there are some who rather believe it to be the modern Sumatra. The ancients had also some obscure knowledge of the peninsula of Malacca, which they called the Golden Chersonesus, and they seem to have examined the gulf formed by that land, which is now the gulf of Cochinchina, or commonly called the gulf of Tonkin. It is somewhat extraordinary that they do not seem to have been acquainted

acquainted with Java, Borneo, and that numerous group of islands which form, in that quarter, the greatest Archipelago in the world. It is equally singular that the Maldives had escaped the observation of these navigators. This seems to prove that they never ventured out into the open sea, but kept close along the shore. Ptolemy indeed says, that his island of Taprobana was surrounded with many hundreds of smaller islands, to some of which he gives names; but all this is involved in impenetrable obscurity.

Of Africa, the ancients knew only those parts which lay along the coast, and to a very small distance inland, if we except Egypt, with which they were well acquainted, at least as far as the cataracts of the Nile, and a little beyond them, as far as the island of Meroe, towards the 20th degree of north latitude. Their knowledge of the coasts of Africa on the side of the Red sea, extended no farther than the shores of that sea, except that part which was dependent on Egypt; the interior of the country being inhabited by ferocious and untractable people. They were still less acquainted with the countries which lay beyond the strait, and Ptolemy appears to have given no credit to the navigators who were said to have sailed round that part of the world, for he has left the continent of Africa imperfect towards the south. Strabo and Pomponius Mela were, however, decidedly of opinion that Africa was a peninsula, and that it was joined to the rest of the continent only by that narrow neck of land which is now called the isthmus of Suez. The ancients seem to have had no knowledge of that large and beautiful island of Madagascar, unless we suppose that Ptolemy had some imperfect acquaintance with it, under the name of the island Menuthius. The coast of Africa upon the Mediterranean sea, was once covered with towns, dependent on the Roman empire, flourishing and polished, while it presents at present nothing but a nest of pirates, whom the jealousy of the great commercial nations supports, to the disgrace and prejudice of civilized states. Proceeding from the straits of Gadez or Gibraltar, they had become acquainted with the coast as far as a cape which they called Hesperion-Keras, probably the modern Cape de Verd, or the cape that lies a little to the west of it, though in the maps of Ptolemy it is thrown a little back inland. The Fortunate islands, or the Hesperides, at present the Canaries, better known by name than in reality, seem to have been the boundaries of ancient geography to the west, as the Seres and Sine were to the east. It appears, however, that the Cape de Verd islands were not entirely unknown to the ancients, and they are probably the same with what were then called the Gorgades or Gorgones, which were supposed to be two days sail to the west of Hesperion-Keras.

There is little doubt (says Mr Pattefon) concerning the names by which most of the principal countries of Europe were known to the ancients; nor is there any difficulty in disposing the chief nations, which ancient writers have enumerated in the south-west part of Asia or on the African coast of the Mediterranean; but with the north and north-east parts of Europe, about two thirds of Asia towards the same quarters, and nearly the same proportion of Africa towards the south, they appear to have been wholly unacquainted. Of America they did not even suspect the existence; and if it ever

happened, as some writers have imagined, that Phoenician merchant ships were driven by storms across the Atlantic to the American shores, it does not appear that any of them returned from thence to report the discovery.

The names of provinces, subdivisions, and petty tribes, mentioned by ancient authors, in those countries which were the chief scenes of Roman, Grecian, or Israelitish transactions, are almost as numerous as in a modern map of the same countries; and the situations of many of them can be very nearly assigned: but the limits of each, or indeed of the states or nations to which they belonged, can, in very few instances, be precisely fixed. Thus the southern boundaries of the Sarmatæ in Europe, cannot be ascertained within a degree at the nearest; and in France, neither the limits of the people called the Belgæ, Celtæ, and Aquitani; nor those of the Roman divisions, viz. Belgica, Lugdunensis, Aquitania, Narbonensis, and the Province, can be laid down, in many places, but by a hardy conjecture. The same observation may be justly applied to the Tarraconensis, Lusitania, and Betica of Spain; to the Cauca, Catti, Suevi, &c. of Germany; and, above all, to the Britannia prima et secunda, and other divisions of the Roman government in Britain: of which not only the limits, but the situations are still in dispute. *

During the middle ages geography, as well as most other arts and sciences, seems rather to have gone back-wards than advanced. The weakness of the Roman empire,

the relaxation of military discipline, the boundless passion for luxury and pleasure, and the continual incursions of the barbarous nations, while they contributed to hasten the fall of the western empire, also accelerated the ruin of the arts. It seems as if these destructive hordes of barbarians, the Goths, the Huns, and the Vandals, had enveloped the whole world in one profound and universal ignorance. This darkness, which overspread the whole of Europe, did not permit geography to make any advances for a very considerable time. There were indeed some navigators who investigated countries that were still little known, but they were so ignorant, that they afford us very little new light. There was one named Cosmas, who made a voyage to India, which procured him the name of Indo-Pleustes, and who gave an account of his voyage under the title of Sacred Geography. This man was so egregiously ignorant, as to believe that he had discovered that the earth was a plane, and that the diversity of the seasons, and the inequality of the days and nights, were owing to a very high mountain situated to the north, behind which the sun set to a greater or less depth.

The voyages of the Arabians to the East Indies (see the history of COMMERCE), contributed to throw the farther light on that extensive part of the globe. Conquerors of the countries on the Red sea, and enthusiastic propagators of their religion, they carried their arms as far as the extremity of India. We see them in the 9th century extending to China; and Renaudot has published two of their narrations, in which we can trace with tolerable accuracy, the places visited by their authors. The island of Serendib, so celebrated in their tales, is certainly the modern Ceylon; for dir or dir, in the Malay language, signifies island, so that Serendib, signifies the island of Seren or Selan. Farther, these relations

History. relations do not give us as favourable an idea of the Chinese as we derive from their own history; on the contrary, if we may believe these Arabian travellers, this people were, even at that time, in a state not very civilized.

33
Modern discoveries. We are now arrived at the modern period of our history, during which the most important discoveries have been made, and our knowledge of the habitable globe more than doubled. The discoveries and improvements during this period are so numerous, that it will be impossible to give here any thing more than a chronological view of the most remarkable, referring for a detailed account of them to the geographical and historical articles in this work.

The taste for voyages of discovery began in Europe soon after the revival of literature in the 15th century, just before the commencement of which, namely, in the reign of Henry III. king of Spain, about the year 1395, the Canary islands were more fully surveyed than at any former period.

1415. Prince Henry III. son of John king of Portugal, sailed round the coast of Africa.

1417. The Canary islands were subdued by Bethancourt, nephew of the admiral of France.

1420. The island of Madeira was examined by John Gonfalo and Tristan Vaz, two Portuguese.

1446. Cape de Verd was discovered by Dennis Fernandez.

1487. The Cape of Good Hope was discovered by Bartholomew Diaz. The discovery of this cape led the way to that of the new world. This great event, which gave a new flight to the genius of mankind, is one of the most important in the history of geography. A particular account of this discovery will be found under the article AMERICA. The following are the dates of the principal geographical discoveries which have taken place between that of Columbus, and the voyages of our celebrated navigator Cook.

1496. Florida, by Sebastian Gabot, an Englishman.

1498. The Indies, by Vasco di Gama.

1499. The river of Amazons, by Yanez Pinçon.

1500. Brazil, by Alvarez Cabral, a Portuguese.

1504. Newfoundland, by some Normans.

1518. Mexico, by Ferdinand Cortes.

1519. The straits of Magellan, South sea, and Philippine islands, by Ferdinand Magellan.

1525. Canada, by Jean Verrazani, a Florentine, sent by Francis I. of France.—Peru, by F. Pizarro of Spain.

1527. New Guinea, by Alvaro de Salvedra.

1534. Chili, by Diego Almagro.

1535. California, by Ferdinand Cortes.

1567. The islands of Solomon, by Alvaro de Mendoza.

1618. New Holland, by Zechaen.

1642. Van Dieman's land, by Abel Jansen Tasman.

1643. Brewer's land.

1654. New Zealand.

1678. Louisiana, by Robert Cavelier de La Salle, governor of Frontinac.

1700. New Britain, by Dampier, an Englishman.

1739. Cape Circumcision, contested between the French and English. Said by Montoula to be discovered by two French vessels.

1767. The island of Taiti, by Wallis, an Englishman.

1778. The Sandwich islands, by Cook.

Within this period there are reckoned 25 voyages round the world, viz. those of Magellan, Drake, Cabot, Number of 34
vendish, Noort, Spilburg, Lemaire, L'Hermitte, Cle-voyages
pington, Careri, Shelvack, Dampier, Cowley, Woodes round the
Rogers, Le Gentil, Anson, Wallis, Roggewein, Bou- the world.
gainville, Sarville, Dixon, three voyages of Cook, La
Peyrouse, Marchand, Vancouver, and Pages.

Within these few years, very considerable light has been thrown on the state of our geographical knowledge, by several valuable voyages and travels that have lately appeared. The discoveries that have been successively made in the great South sea, and in other parts of the world, especially the extensive island of New Holland, are now so fully established, as to add considerably to the certainty of our geographical knowledge; and the voyages of Cook, La Peyrouse, and Vancouver, have afforded us more exact surveys of the coasts of these countries than we could, some years ago, have dared to hope for. The accounts of the late embassies to China, Tibet and Ava, afford many authentic materials for a modern system of geography, the place of which must have been supplied by more remote and doubtful information. From the latter of these accounts we are become familiarly acquainted with an empire (that of the Birman), which a short time ago was scarcely known (see ASIA, 81—152). Our knowledge of Hindostan and the neighbouring countries has been greatly extended by the researches of the Asiatic Society, and some other late works; while our acquaintance with the interior of Africa has been rendered less imperfect by the exertions of the African Society, and by the travels of Park, Brown, and Barrow; and the northern boundaries of America, even as far as the sea which appears to surround the northern extremity of that vast continent, have been more fully disclosed by the journeys of Hearne and Mackenzie.

The late voyage of Turnbull, however insignificant it may be in other respects, has at least the merit of enlarging our knowledge of the manners and political transactions of the South sea islanders, and of introducing to our acquaintance, in the person of Tamahama, the chief of Owhyhee, a sovereign, who, in ambition and desire of improvement, bids fair to vie with Peter the Great; and to transform a nation of savages, to a civilized people.

With all the advantages which geography has lately received, the science is still far from being perfect; and facts of geo-
the exclamation which D'Anville is said to have made geography.
in his old age, "Ah! mes amis, il y a bien d'erreurs dans la géographie"—Ah! my friends, there are a great many errors in geography, may still be applied with considerable justice. Many points in the science have been but very lately ascertained. Thus, the extent of the Mediterranean sea was almost unknown at the beginning of the 17th century, although it is now almost as exactly ascertained as that of any country in Europe. In a book published by Gemma Frisius, de orbis divisione, in 1530, we find the difference of longitude between Cairo in Egypt and Toledo in Spain stated at 53° instead of 35°, and other measures of extent are proportionally erroneous. Not many years ago there was an uncertainty with respect to the extremity of the Black sea and the Caspian, to the amount of 3° or 4°; and

History. and so lately as the year 1769, the longitude of Gibraltar and of Cadiz was not known within half a degree.

Many parts of the geography of Europe are still very defective; Spain and Portugal have been but imperfectly explored, and European Turkey is still less known. It may appear extraordinary that we have yet no correct chart of the British channel, though we are assured by Major Rennell that this is the case; and it has been proved by the trigonometrical surveys of Britain that have yet been published, that there are many gross errors in our best county maps. We have had occasion to remark that geography has sometimes been retrogressive, and there cannot be a greater proof of the truth of the observation, than that in a map of the Shetland islands, published not long ago, by Preston, they are represented as too large by one third, both in length and breadth, and their relative positions are very inaccurate, though in the maps of the same islands published before the year 1750, they are laid down with much greater accuracy, as appears from surveys made by order of the late king of France, and from the maps published by Captain Donelly, and at Copenhagen, in the year 1787.

In Asia we are imperfectly acquainted with Tibet, and some other central regions; and even Persia, Arabia, and Asiatic Turkey, are but little known. Of Australasia, or New Holland, and New Guinea, almost nothing is known except the coasts, and a great part of them towards the south has been but imperfectly explored. Of Polynesia, or the numerous islands in the South Pacific ocean, we are also very ignorant; and in the Pacific ocean, particularly towards the south pole, many discoveries probably remain to be made.

Our ignorance of the central parts of Africa is notorious, and the improvement of our geographical knowledge in that quarter has, for some years, been a favourite object. It may admit of doubt, however, whether this object will be speedily attained, as the obstacles to investigation in those inhospitable tracts, seem nearly insurmountable by human prudence and courage. Even the shores of Africa have not been completely surveyed, especially those towards the south and east.

America has of late been much more fully explored than at any former period: but still the western parts of North America, and the central and southern regions of South America, are very little known; and the Spanish settlements towards the north are scarcely known, except to their own inhabitants.

The science of geography will probably be never perfectly understood, as, besides the numerous obstacles which oppose the progress of the traveller, it is scarcely possible that exact trigonometrical surveys of every place and country, the only certain method of ascertaining their exact situations and relative positions, can be made.

Political geography must ever remain the most uncertain part of the science. New changes are perpetually taking place in the relations of neighbouring states, according as ambition, tyranny, or commercial convenience dictates. Territory is transferred, by cession or by conquest, from one nation to another. Whoever will compare the relations of the European states, as they

appear in the present maps, and in those published half a century ago, will scarcely recognise the countries to be the same. The great divisions indeed remain as before, but the boundaries of most of them are entirely changed. A number of independent states, and in one instance, a large kingdom, have been swallowed up by the unjustifiable ambition of their more powerful neighbours, and their names may be blotted from the map of Europe. The republics of Holland, of Switzerland, of Venice, are no more: the kingdoms of Poland and Sardinia have ceased to exist: the successor of St Peter, who once gave laws to princes, and governed Europe with unbounded sway, is now a wretched exile, and his dominions are doomed to increase the already overgrown power of despotic upstarts. Whether the present generation of emperors and kings, erected by the mighty Napoleon, will remain as long as did the states on whose ruins they have been raised, or are rather ephemeral productions, doomed to perish at the setting of that sun which now gives them life and vigour, is a question which future experience alone can determine.

The limits prescribed to this article do not permit us to enter on a critical examination, or even a characteristic sketch, of the geographical works that have appeared in the modern period of the history of the science; and a bare enumeration of names would be equally tiresome and uninteresting. Some of the best modern works will be mentioned in the sequel; at present we shall conclude this Part in the words of an able judge of the present state of the science.

"The Spaniards and Italians (says Mr Pinkerton) have been dormant in this science; the French works of La Croix and others are too brief; while the German compilations of Busching, Fabri, Ebeling, &c. are of a most tremendous prolixity, arranged in the most tasteless manner, and exceeding in dry names, and trifling details, even the minutest of our gazetteers. A description of Europe in 14 quarto volumes, may well be contrasted with Strabo's description of the world in one volume: and geography seems to be that branch of science, in which the ancients have established a more classical reputation than the moderns. Every great literary monument may be said to be erected by compilation, from the time of Herodotus to that of Gibbon, and from the age of Homer to that of Shakespeare; but in the use of the materials there is a wide difference between Strabo, Arrian, Ptolemy, Pausanias, Mela, Pliny, and other celebrated ancient names, and modern general geographers; all of whom, except d'Anville, seem under graduates in literature, without the distinguished talents or reputation, which have accompanied almost every other literary exertion. Yet it may safely be affirmed, that a production of real value in universal geography requires a wider extent of various knowledge than any other literary department, as embracing topics of the most multifarious description. There is, however, one name, that of d'Anville, peculiarly and justly eminent in this science; but his reputation is chiefly derived from his maps, and from his illustrations of various parts of ancient geography. In special departments Gosselin, and other foreigners, have also been recently distinguished; nor is it necessary to remind the reader of the great merit of Rennell and Vincent in our own country."

IT has been supposed, by the less enlightened part of mankind in all ages, that the surface of the earth is nearly a plane, bounded on all sides by the sky. It was shewn, however, in the article ASTRONOMY, (No 269—272) that the earth is of a spherical figure, and an account was there given of the manner in which the true form of it was determined. Independently of the considerations there detailed, the spherical figure of the earth may be inferred, in a popular view, from the following facts.

1. When we stand on the sea-shore, while the sea is perfectly calm, we easily perceive that the surface of the water is not quite plain, but convex or rounded; and if we are on one side of a broad river or arm of the sea, as the frith of Forth, and with our eyes near the water, look towards the opposite coast, we shall plainly see the water elevated between our eyes and the opposite shore, so as to prevent our seeing the land near the edge of the water.

2. When we observe a ship leaving the shore, and going out to sea, we first lose sight of the hull, then of the sails and lower rigging, and lastly of the upper part of the masts. Again, when a ship is approaching the shore, the first part of her that is seen from the land is the topmast, then the sails and rigging appear, and lastly the hull comes gradually into view. These appearances can arise only from the ship's sailing on a convex surface; as, if the surface of the sea was plain, a ship on its first appearance would be visible, though very small, in all its parts at the same time, or rather the hull would first appear, as being most distinguishable; and, in going out of sight, it would in the same manner disappear at once, or the hull would be the last part of which we should lose sight.

3. Many navigators sent on voyages of discovery, have, by keeping the same course, at length arrived at the port from which they set out, having literally sailed round the globe. This could not happen if the sea were a plain.

4. When we travel to a considerable distance, in a direction due north or due south, a number of new stars successively appear in the heavens, in the quarter to which we are travelling; while many of those in the opposite quarter gradually and successively disappear, and are seen no more till we return in a contrary direction.

5. In an eclipse of the moon, which has been shewn (ASTRONOMY, No 199) to be owing to the obscuration of the moon's surface by the shadow of the earth, the boundary of the obscured part of the moon is always circular. Now, it is evident that no body, which is not spherical, can, in all situations, cast a circular shadow.

The diameter of the earth is generally computed at 7958 miles, though Mr Vince makes it 7930, nearer the medium derived from a comparison of the

polar with the equatorial axis. Taking this last, therefore, as the mean diameter, the circumference will be = 24,912 miles, and consequently the extent of the superficies will be = 197,552,160 miles, of which it is computed that at least two-thirds are covered with water.

In the above computation no account is taken of the mountains and other eminences on the surface of the globe; for, although these are of considerable consequence in a geographical point of view, as they constitute the most natural and remarkable boundaries of countries, and by their influence on the soil and climate of the different regions, contribute in a great degree to form those shades of distinction which diversify the inhabitants of the several quarters of the earth, they are, however, too trifling, when compared with the diameter of so great a body, to make any sensible error in the calculation.

The surface of the earth is exceedingly diversified, al-⁴¹most everywhere rising into hills and mountains, or of the sinking into valleys; and plains of any great extent are extremely rare. Among the most extensive plains, are the sandy deserts of Arabia and Africa, the internal part of European Russia, and a tract of considerable extent in the late kingdom of Poland, now called Prussian Poland. But the most remarkable extent of level ground, is the vast platform of Tibet in Asia, which forms an immense table, supported by mountains running in every direction, and is the most elevated tract of level country on the globe. The chief elevations or mountains that occur, with their elevation, &c. will be mentioned under GEOLOGY. The greatest concavities of the globe are those which are occupied by the waters of the sea, and of these by far the largest forms the bed of the Pacific ocean, which stretching from the eastern shores of New Holland to the western coast of America, covers nearly half the globe. The concavity next in size and importance, is that which forms the bed of the Atlantic ocean, extending between the new and the old worlds; and a third concavity is filled by the Indian ocean. Smaller collections of water, though still large enough to receive the name of oceans, fill up the remaining concavities, and take the names of Arctic and Antarctic oceans.

Smaller collections of water that communicate freely with the oceans, are called seas, (vid. A; fig. 1), and of these the principal are the Mediterranean, the Baltic, the Black sea, and the White sea. These seas sometimes take their names from the country near which they flow; as the Irish sea, and the German ocean. Some large bodies of water, which appear to have no immediate connexion with the great body of waters, being everywhere surrounded by land, are yet called seas; as the Caspian sea.

A part of the sea running up within the land, so as to form a hollow, if it be large, is called a bay or gulf; as the bay of Biscay, gulf of Mexico: if small, a creek, road, or haven.

When two large bodies of water communicate by a narrow pass between two adjacent lands, this pass is called

^{Principles and Practice.}
called a strait or straits (C, fig. 1.) as the straits of Gibraltar, the straits of Dover, or Babelmandel, &c. The water usually flows through a strait with considerable force and velocity, forming what is called a current, and frequently this current always flows in the same direction.

^46
Currents. Thus, in the straits of Gibraltar there is a constant current from the Atlantic into the Mediterranean, though the surface of the latter never seems to be elevated beyond its usual level. There is always a current round Cape Finisterre and Cape Ortelgal, setting into the bay of Biscay, and it has been discovered by Major Rennel, that this current is continued in a direction N. W. by W. from the coast of France to the westward of Ireland and the Scilly islands. Hence he draws this useful practical instruction for navigators who are entering the English channel from the Atlantic, viz. that they should keep no higher latitude than 48° 45', lest they should be carried by the current upon the rocks of Scilly. For want of this necessary precaution, it is said that many ships have been lost on these rocks.

^47
Lakes. A body of fresh water, entirely surrounded by land, is called a lake, loch, or lough (as D, fig. 1), with the exception of the sea above mentioned; as the lake of Geneva, Lake Ontario, Lake Champlain, Loch Lomond, &c.

This term, or its synonyms, loch or lough, is sometimes applied to what is properly a gulf or inlet of the sea, as Loch Fyne in Scotland, and Lough Swilly in Ireland.

^48
Rivers. A considerable stream of water rising inland, and running towards the sea, is called a river; a smaller stream of the same kind is called a rivulet or brook. Vid. E, fig. 1.

^{49
Continents.} The great extent of land which forms the rest of the globe, is divided into innumerable bodies, some of which are very large, but the majority extremely small. There are three very extensive tracts of country, which may all be denominated continents, though only two of them have hitherto been distinguished by that appellation. The most considerable of these continents is what has been called the old world, comprising Europe, Asia, and Africa. The second comprehends North and South America, or what has been denominated the new world, and is little inferior in extent to the former. The third great division forms the country called New Holland.

^50
Islands. A body of land entirely surrounded by water is called an island, (vid. a, fig. 1.) as Britain, Ireland, Jamaica, Madagascar, &c. According to the strict meaning of this definition, the large divisions just mentioned are islands; for it is almost certainly ascertained, that the continent of North America is everywhere bounded by the sea, and it has long ceased to be doubtful that New Holland is in the same circumstances, and it is generally called the largest island in the world. But perhaps it would be better to confine the term to those numberless smaller islands that appear above the surface of the waters. When a number of smaller islands are situated near each other, the whole assemblage is commonly called a group of islands, as b, b. The large assemblages of islands that have been discovered in the South Pacific ocean, have lately been comprehended under the name of Polynesia, constituting a sixth division of the whole earth; the other five being Europe, Asia, Africa,

America, and the islands of New Holland and New Guinea, under the name of Australasia.

A body of land that is almost entirely surrounded by water is called a peninsula, as e, fig. 1.; as the peninsula of Malacca, the Morea, or Grecian Peloponnese, Peninsula, &c. Indeed the continent of Africa may be considered as a vast peninsula, being united to Asia only by the small isthmus of Suez.

The narrow neck of land which joins a peninsula to the main land, or which connects two tracts of country together, is called an isthmus, as d. The most remarkable isthmuses are the isthmus of Darien, connecting the continents of North and South America, and the isthmus of Suez, joining Africa to Asia.

A narrow tract of land stretching far out into the sea, being united to the main land by an isthmus, is called a promontory, and its extremity next the sea, is called a cape; as e, f, fig. 1. The most remarkable capes are the Cape of Good Hope, at the southern extremity of Africa; Cape Horn at the southern extremity of South America; the North Cape at the northern extremity of Europe; and Cape Taimara, at the northern extremity of Asia.

It may assist the memory of the young geographer, to compare together the above divisions of land and water. We may remark that the large bodies of land, called continents, correspond to the extensive tracts of water called oceans; that islands are analogous to lakes; peninsulas to seas or gulfs; isthmuses to straits; promontories to creeks, &c.

The inhabited parts of the earth are calculated to occupy a space of 38,990,569 square miles, of which the four quarters into which the globe is usually divided are supposed to have the following proportions:

The whole population of the earth has been computed at 700,500,000 souls; and of these

Hence the proportional number of inhabitants to every square mile in each quarter is as follows:

CHAP. II. Of the Construction and Use of the Globes.

SECT. I. Description and Use of the Terrestrial Globes.

FOR the purpose of representing more accurately the Nature of globe which we inhabit, geographers have long had recourse to spherical balls, on the face of which are drawn the various divisions of the earth, and which are fitted up with such an apparatus, as enables us to illustrate and explain the phenomena produced by the motions

tions of the earth, and the different situations of its various inhabitants. The ball thus prepared, is called an artificial globe, and what we have described is properly the terrestrial globe, so called to distinguish it from another of a similar form, and furnished in a similar manner, but the surface of which represents the various assemblages of stars or constellations that appear in the heavens, and therefore this is called the celestial globe.

In order to ascertain the relative positions of places and countries on the earth, certain circles are supposed to be drawn on its surface, analogous to those which were mentioned in ASTRONOMY, as supposed to be drawn in the heavens. As these circles are really represented on the artificial globes, it will be proper here to consider a little more particularly their nature and uses.

As the earth turns about on an imaginary axis, once in 24 hours, the artificial globe is furnished with a real axis, formed by a wire passing through the centre, and on which the globe revolves. The two extremities of this axis are its poles, the one being called the north, and the other the south pole.

A great circle drawn on the globe, at an equal distance from both poles, is the equator or equinoctial line, and represents on the globe a similar circle, supposed to be drawn round the earth, and distinguished by the same names. By sailors this is commonly called the line, and when they pass over that part of the water, where it is imagined to be drawn, they often make use of various superstitious ceremonies. The two parts of the globe into which it is divided by the equator, are called the northern and southern hemispheres.

The equinoctial line on the earth passes through the middle of Africa, in the almost unknown territories of Macoco, and Monemugi, traverses the Indian ocean, passes through the islands of Sumatra and Borneo, and the immense expanse of the Pacific ocean; then extends over the province of Quito in South America, to the mouth of the river Amazons.

As every circle is supposed to be divided into $360^\backslash circ$, so the equator is thus divided on the artificial globe.

Through every $15^\backslash circ$ of the equator there is drawn on the globe a great circle passing through the poles. These circles are called meridians, because when the sun in his apparent course from east to west reaches the corresponding circle in the heavens, it is noon on that part of the earth over which the meridian is supposed to pass. Properly speaking, every place on the earth has its own meridian, though to prevent confusion, these circles are drawn on the artificial globe,

only through every $15^\backslash circ$ of the equator. To supply the place of the other meridians, the globe is hung in a strong brazen circle, which is called the brazen meridian, or sometimes only the meridian. The brazen meridian, like the equator, is divided into $360^\backslash circ$, but these are marked by nineties on each quadrant, being on one half of the meridian numbered from the equator to the poles, and on the other half from the poles to the equator. On the opposite side of the brazen meridian there are two concentric spaces, which are divided into degrees corresponding to the months and days of each month, the degrees being marked on concentric spaces from the north pole to about $23\backslash frac\{1\}\{2\}^\backslash circ$ both ways. The use of these divisions will appear hereafter (B).

Through every tenth degree of the meridians, there are drawn on the globe circles parallel to the equator, which, for a reason that will appear presently, are called parallels of latitude.

Before we proceed in describing the other circles, &c. of the artificial globe, we shall here make a few remarks on the uses of the equator, the meridians and parallels (C).

The equator serves to measure the distance of one place from another, either to the eastward or westward, and this distance is called the longitude of the place. The meridians serve in like manner to measure the distance of one place from another in a direct line north or south of the equator, and the distance of the place thus measured is called its latitude.

The longitude and latitude of places may be illustrated in the following manner. Let $PEP\text{'}Q$ (fig. 3) represent the earth or the globe, (supposed to be transverse) whose axis is $PCP\text{'}$, the north pole being $P$, and the south pole $P\text{'}$; and let $EAQR$ represent a circle passing through the centre $C$, in a direction perpendicular to the axis $PP\text{'}$. This circle corresponds to the equator, and it divides the earth of the globe into two hemispheres, $EPQ$ being the northern, and $EP\text{'}Q$ the southern hemisphere. Let $G,\; I,\; K$, represent the situations of three places on the surface of the globe, through which let the great circles $PKP\text{'},\; PIP\text{'},$ and $PGP\text{'}$, be drawn, intersecting the equator $EQ$, in $n,\; m,\; a$, respectively. The circles are the meridians of the places $K,\; I,\; G$. As every circle is supposed to be divided into $360^\backslash circ$, there must be $90^\backslash circ$ from each pole to the equator. Hence the latitude of the place $K$ is measured by the degrees of the arc intercepted between $K$ and $n$, and the latitudes of $G$ and $I$ are measured by the degrees of the arcs intercepted between $G$ and $a$, and $I$ and $m$ respectively. These latitudes will be called north

(a) The meridians are properly only semicircles, reaching from pole to pole, and of these there are twenty-four.

(c) In Geography, as in other sciences, there are two methods of conveying instruction. One is, to lay down the principles of the science first, and afterwards apply these to the practice of it; the other method is, to combine the principles and practice in one view. The former is usually considered as the more scientific, but we are inclined to think that the latter is often to be preferred, as being less dry and tedious, especially to a general reader. We have here, therefore, chosen to explain the nature of latitude and longitude, and the problems respecting them, before completing the description of the globe. We shall proceed in the same manner, uniting as far as possible, the principles and practice in one view. Making, therefore the terrestrial globe our text book, we shall thence explain the principles of geography, rather than detail these in a separate section, and afterwards illustrate them by the globe.

Principles and Practice. north latitudes, because the places lie in the northern hemisphere. Let there be two other places, WV, in the southern hemisphere; the latitude of W will be measured by the degrees of the arc intercepted between W and $a$; and the latitude of V by the arc intercepted between V and $m$; and these will be called south latitudes. Further, let the circle $c,\; e,\; d,\; v,\; G$, be drawn parallel to the equator; this circle is called a parallel of latitude, and as it does not pass through the centre, it is evidently less than the equator, or it is a small circle. Now, all the arcs, such as $R,\; e,\; a,\; G$, &c. intercepted between the parallel and the equator, must be equal, since the circle is parallel to the equator; and hence every point in this parallel, or every place on the earth through which it is supposed to pass, has the same latitude.

Latitude is the same all over the earth, being constantly measured from the equator to the poles.

The longitude of a place is measured by the degrees of an arc of the equator, intercepted between some particular meridian, and the meridian passing through the place. Thus, suppose $G$ to represent the particular meridian, and $m$ to represent the place whose longitude is required; the longitude of $m$ is measured by the arc $ma$ of the equator, intercepted between $a$, the point where the meridian of $G$ meets the equator, and $m$ the point of the equator where it is cut by the meridian of the place $m$. The particular meridian from which we begin to reckon the degrees of longitude is called the prime or first meridian, and it is different in different countries.

The method of estimating the distances of places by longitudes and latitudes, is of considerable antiquity, and was employed by Eratosthenes, who first introduced a regular parallel of latitude, which began at the straits of Gibraltar, passed eastwards through the island of Rhodes to the mountains of India; all the intermediate places through which it passed being carefully noted. Soon after drawing this parallel through Rhodes, which was long considered with a degree of preference, Eratosthenes undertook to trace a meridian, passing through Rhodes and Alexandria, as far as Syene and Meroë. Pythias of Marseilles, according to Strabo, considering the island of Thule as the most western point of the then known world, began to count the longitude from thence, while Marianus of Tyre placed their first meridian at the Fortunate islands, or the Canaries; but they did not determine which was the westernmost of these islands, and consequently which ought to serve as a first meridian. Among the Arabians, Alfragan, Albategnus, Nassir Eddin, and Ulug Beg, also reckoned from the Fortunate islands; but Abulfeda began to reckon his longitude from a meridian $10^\{\backslash circ\}$ to the eastward of that of Ptolemy, probably because it passed through the western extremity of Africa, where, according to him, were situated the pillars of Hercules; or because it passed through Cadiz, which was at that time rendered famous by the conquests of the Moors in Spain.

When the Azores were discovered by the Portuguese in 1448, some geographers made use of the island of Tercera as their first meridian. Other geographers, as Blaeu, father and son, placed the first meridian at the Peak of Teneriffe, a mountain so far elevated above the sea, that it may be easily known by navigators;

VOL. IX. Part II.

Principles and Practice. while others have made the island of St Philip, one of the Cape de Verds, the first meridian, because they conceived this to be the place where the magnetic needle had no variation. For a long time it was customary to reckon the longitude in most countries from the isle of Ferro, one of the Canary isles; but it is now customary for each nation to reckon the longitude, either from the metropolis of the country, or from the national observatory situated near it. Thus in France, Paris is the first meridian, and in Great Britain, the Royal Observatory of Greenwich. As in several good maps, the isle of Ferro is still used as a first meridian, it may be proper to remark, that the observatory at Greenwich lies $17^\{\backslash circ\}\; 45\text{'}$ to the east of Ferro. Hence it is very Method of reducing longitudes to the same meridian. easy to reduce the longitude of Ferro to that of Greenwich; for if the longitude required be east, we have only to subtract $17^\{\backslash circ\}\; 45\text{'}$ from the longitude of Ferro, and the remainder is the longitude east from London; on the other hand, if the place be west from Ferro, we obtain the longitude west from London by adding to that of Ferro $17^\{\backslash circ\}\; 45\text{'}$. If the place lies between Ferro and London, its longitude from London will be obtained by subtracting its longitude east from Ferro from $17^\{\backslash circ\}\; 45\text{'}$. It is evident that by the reverse of this method, we may reduce the longitude from London to that of Ferro.

In the diagram referred to above, if $G$ represent the observatory of Greenwich, $a$ will be the point from which we begin to reckon the degrees of longitude, and all places situated to the east of $a$, such as $R,\; m$, will have east longitude, while those situated to the west, as $n$, will have west longitude. In reckoning the longitude, we sometimes number the degrees only as far as $180^\{\backslash circ\}$, but at other times they are numbered all round the equator from the point $a$; for instance, $180^\{\backslash circ\}$, till we come to $a$ again; hence reckoning in the direction $a,\; R,\; m$, we should say that every place was in so many degrees east longitude, while if we reckoned in the direction $n,\; E$, we should say that all the places had so many degrees west longitude all round the equator. To accommodate the globes to both these modes of reckoning the longitude, the equator is usually divided both ways, in a continued series from $a$ at the first meridian to $360^\{\backslash circ\}$.

It is evident, that as the parallels of latitude become smaller as they approach the poles, the arcs of these parallels intercepted between the same two meridians will be also smaller as we proceed from the equator to the poles, though in fact they consist of the same absolute number of degrees. Hence it will be easy to see that a degree of longitude must be smaller towards the poles than at the equator, and must become gradually smaller and smaller till we arrive at the poles, where it will be equal to nothing. Thus the arc $Gv$ contains the same number of degrees as the arc $am$, though the former arc is much smaller than the latter. As a degree of longitude is therefore different at every degree of latitude, it becomes necessary to ascertain the relative proportion between the two; and for this purpose the following table has been constructed, which shows the absolute measure of a degree of longitude in geographical miles and parts of a mile for every degree of latitude, taking the degree of longitude at the equator, equal to 60 geographical miles.

As it is often more convenient to estimate degrees of longitude in English statute miles, we have added the following

Hence it appears that the degrees of latitude are all equal, and that a degree of longitude at the equator is equal to a degree of latitude, as each is $\backslash frac\{1\}\{360\}$th of a great circle. In the second of the above tables, a degree of longitude at the equator is estimated at 69.2 English miles, or about 69$\backslash frac\{1\}\{2\}$. The length of a degree in miles is usually estimated at 69$\backslash frac\{1\}\{2\}$, but this is too much. Hence, to reduce degrees of latitude, and those of longitude near the equator, to English miles, it is necessary to multiply them by 69.2, or, if great accuracy is not required, by 70.

PROBLEM I. To find the latitude and longitude of a given place.

Bring the place below the graduated edge of the

brazen meridian, and the degree of the meridian that lies immediately over the place is its latitude. Observe where the meridian cuts the equator, and that degree will be the longitude of the place.

Example. To find the latitude and longitude of Edinburgh.—Bringing Edinburgh below the meridian, we find over it nearly the 56th degree of north latitude (55° 58'), and the point where the meridian cuts the equator is nearly 3$\backslash frac\{1\}\{2\}$ (3° 12' W. Long.) degrees west from London.

N. B. The longitude and latitude of places cannot be ascertained exactly by the globes, as these are not calculated to show the fractional parts of a degree; but they may be found with sufficient correctness for ordinary purposes.

COROLLARY 1. The difference of latitude and longitude

Principles and Practice. Latitude between two places is found by subtracting the less from the greater, if they lie the same way, i. e. north or south, east or west; or by adding the two together, if they lie in a different direction.

COR. 2. Those places that have the same latitude with any given place are found, by bringing the given place to the meridian, and observing what places pass under the same degree, while the globe is turned round.

COR. 3. Those places which have the same longitude with a given place, are found by bringing the place to the meridian, and observing what other places lie under the graduated edge, while the globe is at rest.

PROBLEM II. The latitude and longitude of a place being given, to find the place itself on the globe.

Turn the globe till the given longitude comes under the brazen meridian; then mark the given latitude on the meridian, and immediately below it is the place required.

Example. What place is situated in $48^\{\backslash circ\}\; 23\text{'}$ N. Lat. and $4^\{\backslash circ\}\; 29\text{'}$ E. Long. from Greenwich? Ans. Brest in France.

As the sun, in his apparent motion round the earth, measures a great circle in about 24 hours, or in one hour passes over $\backslash frac\{1\}\{24\}$th of such circle, or $15^\{\backslash circ\}$; it is evident that all places which lie $15^\{\backslash circ\}$ west of any meridian, must have noon or any other time of the day, an hour later than those situated under that meridian; and that all places which lie $15^\{\backslash circ\}$ east of any meridian, must have the same times of the day an hour sooner. Hence, because the meridians drawn on the globe make a difference of an hour each in the time of places, they are sometimes called hour-circles; and the longitude of places is sometimes reckoned in time as well as in degrees.

Degrees of longitude are reduced to hours and minutes, and v. v. by allowing an hour for every $15^\{\backslash circ\}$, and four minutes for every degree.

Though the meridians on the globe are sometimes called horary circles, this name is generally confined to a small brass circle, which is adapted to one or each pole, and graduated into twice twelve hours; so that an index fixed to the axis, or the meridian, points out the several hours of day and night as the globe revolves.

In globes of the old construction the hour circles are fixed on the outside of the meridian, but this prevents the meridian from being moved quite round, which is required in some problems.

Mr Joseph Harris, formerly assay-master of the mint, contrived an ingenious method of remedying this inconvenience. He placed two horary circles between the meridian and the globe, one at each pole, and they were fixed tightly between two brass rollers, placed about the axis, so that when the globe was turned, they were carried round with it, while the edge of the brazen meridian served as an index to cut the horary divisions. A globe, thus furnished, serves universally and readily for performing problems in both northern and southern latitudes; and also in places near the equator; whereas, in globes of the old construction, the axis and horary circle prevent the brazen meridian from being moved quite round in the horizon.

The construction of the hour circles was rendered somewhat more simple by Mr G. Wright of London. In his globes, there are engraved two hour circles, one at each pole, on the map of the globe, each circle being divided into a double set of 12 hours, as in the usual hour circles; but here the hours are numbered both to the right and left. (See fig. 4.) The hour hand, or index, is placed below the brazen meridian, in such a way that it may be moved at pleasure to any required part of the circle, and remain there sufficiently steady during the revolution of the globe on its axis, being entirely independent of the pole. In this manner the motion of the globe round its axis, carrying the hour circle, the time is pointed out by the stationary index.

In the globes constructed by the late Mr George Adams, the equator is made to answer the purpose of an hour circle, by means of a semicircular wire placed in its plane, (see Q F, fig. 5.) and carrying two indices F, one on the eastern, the other on the western, side of the brazen meridian. The method of using these indices will be shown presently. In these globes the equator is also marked with twice 12 hours, which increase from east to west, the hours to the west of the first 12 being afternoon hours.

PROBLEM III. The hours at any place being given, to find what hour it is at any other place.

a, By the ordinary globes.

Bring the place at which the hour is given to the meridian, and set the index of the hour circle to the given hour. Then turn the globe till the other place comes under the meridian, and the index will now point to the hour required.

N. B. Where there is no index, the edge of the meridian will in both cases point out the hour.

b, By Adams's globes.

The steps are here the reverse of the former. Bring the place at which the time is required to the brazen meridian, and set the index to the given hour. Then turn the globe till the other place comes below the meridian, and the index will show the time required.

N. B. In the ordinary globes, where the hour circle is usually marked with two sets of figures, it is proper, in performing this problem, to make use of that set which increases towards the right hand, observing that whichever XII. is fixed on for noon, the hours to the right or east of this are hours P. M. and those to the left or west are hours A. M. On Adams's globes the contrary of this takes place, from the hours being marked on the equator. They increase from east to west, and, of course, those to the east of XII. are morning hours, and those to the west of it afternoon hours.

Example 1. When it is noon at London, what hour is it in the Society Isles? Ans. Two A. M.

Ex. 2. When it is 3 P. M. at Edinburgh, what hour is it at Delhi in Hindostan? Ans. Thirty minutes past eight P. M.

PROBLEM IV. Having the hour at any place given, to find all those places where it is noon.

a. By the ordinary globes.

Bring the given place to the meridian, and set the index to the given hour. Then turn the globe till the index point to 12 at noon, and the places then under the meridian are those required.

b. By Adams's globes.

Bring the given place to the meridian, and set the index to 12 at noon. Then turn the globe till the index shall point to the given hour; and all the places then under the meridian have noon at that time.

Ex. 1. It is now 30 min. past 10. A. M. at Edinburgh; In what places is it noon? Ans. Near Stockholm; at Dantzic, Breslaw, Presburg, Vienna, Pofega, Ragusa, Tarento, and the Cape of Good Hope.

Ex. 2. It is now midnight at London; Where is it noon? Ans. In the north-east parts of Asia, in the middle of Fox isles; at the Friendly isles (nearly), and at the east cape of New Zealand.

From the different situation of places with respect to latitude and longitude, the inhabitants of these places received from the ancients denominations that are still retained.

Thus, those places which have the same longitude, or are situated under the same meridian, but are in opposite latitudes, the one lying as many degrees to the north of the equator as the other lies to the south of it, are said to be ANTÆCI to each other. From this definition it is evident, that those places situated under the equator have no antæci.

The appearances arising from the changes of the heavenly bodies are different in the opposite places. Thus, 1. The days of the one are equal to the nights of the other, and vice versa; but they have noon, midnight, and all the other hours at the same time. 2. They have contrary seasons at the same time: when it is summer at one place it is winter at the other, and so of spring and autumn. 3. The stars that never set at one place, never rise at the other, and vice versa.

Again, those places that have the same latitude, or are under the same parallel, but are in opposite longitudes, i. e. lie under opposite arcs of the same meridional circle, or 180° from each other, are said to be PERIÆCI to each other. Those places which may be situated at the poles, have evidently no periæci.

The celestial appearances to the periæci are as follow. 1. The length of the day or night is the same to both places; but the hours, though distinguished by the same numbers, are contrary; noon at the one being midnight at the other; and any hour in the forenoon at the one being the same of the afternoon to the other. 2. Both places have the same seasons of the year at the same time. 3. The same stars that never rise or set to one place, also never rise or set to the other. 4. The heavenly bodies rise in the same point of the horizon at both places, and continue for the same interval above or below it.

Lastly, Those places which are situated directly opposite to each other, by a distance equal to the diameter of the earth, are said to be ANTIPODES to each

other. If we conceive a line through the centre of the earth, and terminated in two points of its surface, these extreme points are antipodes to each other. Thus, the city of Lima in Peru is nearly the antipodes to Siam in the East Indies; and Pekin in China has for its antipodes Buenos Ayres in South America. These places are always in opposite longitudes, and (except under the equator) in opposite latitudes.

The celestial appearances to the antipodes are these. 1. The hours are contrary, as to the periæci. 2. The days of the one are of the same length with the nights of the other; hence the longest day to one is the shortest to the other, and vice versa. 3. They have contrary seasons at the same time. 4. Those stars which, at one place are always above the horizon, are, to the other, always below it. 5. When the heavenly bodies are rising at one place, they are setting at its antipodes, and vice versa. For various opinions respecting the antipodes, see the article ANTIPODES.

The antipodes of any place are the periæci to the antæci of that place; and the antæci to their periæci. This will account for the method presently described of finding the antipodes on the globe.

PROBLEM V. To find the antæci to any given place. Problems.

Bring the given place to the meridian, and thus ascertain its latitude. Then count from the equator towards the opposite pole as many degrees as are equal to the latitude of the place; and the point where this reckoning ends is the place required.

Ex. 1. Where are the antæci to the Cape of Good Hope? Ans. At Malta nearly.

Ex. 2. What people are the antæci to the inhabitants of Quebec in North America? Ans. The inhabitants of Patagonia in South America.

PROBLEM VI. To find the periæci of any given place.

Bring the given place to the brazen meridian, and set the horary index to the upper XII. Then turn the globe till the index point to the lower XII. The place which is then below the meridian in the same latitude with that of the given place, is the situation required.

Ex. 1. Where are situated the periæci of Newcastle upon Tyne? Ans. In the Aleouki or Fox islands.

Ex. 2. Required the periæci to California in North America. Ans. Near the mouth of the river Indus.

PROBLEM VII. To find the antipodes to any given place.

Find the antæci of the given place (by Problem V.) and then find the periæci of the latter (by Problem VI.) This last is the place required.

Ex. 1. It is required to find the antipodes of London. Ans. The latitude of London is 51° 31' N. the antæci to this, or 51° 31' S. on the prime meridian, is in the south Atlantic ocean; the periæci to this is in 180° W. Long. and 51° 31' S. Lat. a little to the south of the islands of New Zealand. The inhabitants of the southern island of New Zealand are therefore the nearest antipodes to London.

Several other circles besides those which we have mentioned are described on the artificial globe, and are supposed to be drawn on the earth. These we shall now proceed to describe, and explain their geographical uses.

Principles and Practice. The Ecliptic (ASTRONOMY, N^o 43.) is a great circle drawn on the globe, crossing the equator obliquely in two points, called the equinoctial points. (ASTRONOMY, N^o 44.) This circle extends on each side of the equator to the latitude of 23° 28', and is divided into 12 great parts corresponding to the 12 signs of the zodiac (see ASTRONOMY, N^o 52.), and marked with their characters, and each sign is subdivided into 30 degrees. The ecliptic has also its poles, which are two points that are distant 90° every way from the circle on each side. As the ecliptic declines from the equator 23° 28', its poles are consequently distant from those of the equator, or of the globe, by the same measure. This circle properly belongs to the celestial globe, but as it is extremely useful in performing many geographical problems, it is always drawn on both globes, and requires to be noticed here, since it determines the position of several of the circles which we are about to mention.

72 The Ecliptic.
73 Tropics.
74 Polar circles.

Through those two points of the ecliptic, where it is at the greatest distance from the equator, there are drawn on the globes two circles parallel to the equator, called tropics. That in the northern hemisphere is called the Tropic of Cancer, as it passes through the sign Cancer; and, for a similar reason, that which is in the southern hemisphere is called the Tropic of Capricorn. The two points through which they are drawn are called solstitial points. The imaginary line which corresponds to the tropic of Cancer on the earth passes from near Mount Atlas on the western coast of Africa, past Syene in Ethiopia: thence, over the Red sea, it passes to Mount Sinai, by Mecca the city of Mahomet, across Arabia Felix to the extremity of Persia, the East Indies, China, over the Pacific ocean to Mexico, and the island of Cuba. The tropic of Capricorn takes a much less interesting course, passing through the country of the Hottentots, across Brasil, to Paraguay and Peru.

If the poles of the ecliptic be supposed to revolve about the poles of the earth, they will describe two circles parallel to the equator, and 23° 28' distant from it. Two such circles are drawn on the globes, and are called Polar Circles, that in the north being called the Arctic Polar Circle, or merely the Arctic Circle, while that in the south is called the Antarctic Polar Circle, or Antarctic Circle.

Both the tropics and the polar circles are marked on the globes by dotted lines, to distinguish them from the other parallels.

75 Colures.

The meridional circles that pass through the equinoctial and solstitial points are called Colures; the former being called the Equinoctial and the latter the Solstitial Colure.

For an account of the variety of day and night in different parts of the globe, see ASTRONOMY, Part II. ch. i. sect. 2.

76 Zones.

By means of the tropics and polar circles, the earth is supposed to be divided into five spaces, to which the ancients gave the name of Zones, or Belts. Thus the space included between the two tropics was called the Torrid Zone, because it was supposed to be so much heated or roasted by the vertical sun, which there prevails, as to be uninhabitable. The ancient terms are still occasionally used, but the countries between the tropics are now more commonly called the Intratropical Regions. The two spaces included between each tropic and its corresponding polar circle were called Temperate Zones, and were distinguished according to their position into Northern and Southern Temperate Zones. Lastly, The spaces between the polar circles and the poles were called the northern and southern Frigid Zones, and were supposed uninhabitable from excessive cold. These last are usually denominated the Polar Regions.

77 Countries between the tropics.

The countries lying between the tropics are the greater part of Africa, the southern parts of Arabia, the eastern and western peninsulas of India; all those clusters of islands lying between the southern continent of Asia and New Holland, called the Sunda, Molucca, Philippine, Pelew, Ladrone, and Carolina islands; the northern half of New Holland, New Guinea, New Britain; most of the groups of islands in the Pacific ocean, as the New Hebrides, New Caledonia, the Friendly and Society isles, the Sandwich and Navigators isles; the West India islands; the greater part of South America; the Cape de Verd islands, and those of St Helena, Ascension, St Matthew, and St Thomas. See the map of the world in Plate CCXXXVI, or the plain chart in Plate CCXXXVII.

All places situated between the tropics have the sun vertical twice in the year, at noon; but the time of the year when this happens is different in the different latitudes; at the equator, the sun is vertical when he is in the equinoctial points, or when he has no declination. The inhabitants of the other intratropical regions have the sun vertical when his declination is equal to their latitude, and on the same side of the equator. Thus, the inhabitants of New Caledonia, about 20° S. Lat. have the sun vertical when his declination is 20° S. To illustrate this, it will be sufficient to observe that, as the ecliptic is that circle in the heavens in which the sun is supposed to move, the sun's rays are perpendicular successively to every point of the earth which lies below that point of the ecliptic in which the sun happens to be, and he will therefore be vertical to all the places through which the ecliptic (continued to the earth) passes successively.

78 Amphiscii.

The inhabitants of the torrid zone have their shadows at noon day sometimes to the south, i. e. when the sun's declination is north, and sometimes to the north, i. e. when the sun's declination is south. They were therefore called by the ancients Amphiscii, from ἀμφί, about, and ῥαί, shadow. See AMPHISCII and ASCII.

79 Countries in the temperate zone.

In the north temperate zone are situated the whole of Europe except Lapland; Barbary, and part of Egypt, in the temperate zone; nearly the whole continent of Asia; a great part of North America; the Azores, and the Canary and Madeira islands.

In the south temperate zone lie the southern part of Africa, the southern half of New Holland, New Zealand, and the southern part of South America.

In the temperate zones the sun is never vertical, and the length of the days and nights differs much more than in the torrid zone.

80 Heteroscii.

The inhabitants of these regions have their shadows at noon always in the same direction; those in the north temperate zone having them directed to the north

Principles and Practice. north, and those in the southern zone, towards the south. They were hence called by the ancients Heteroscii. See HETEROSCII.

86 Countries in the frigid zones. The countries that are situated in the northern frigid zone, are Lapland, Spitzbergen, Nova Zembla, the northern parts of Asia and America, and part of Greenland.

No land has yet been discovered within the south polar circle, though it was long supposed that a large continent was situated there, which was called Terra Australis Incognita. Our celebrated navigator Cook made many attempts to penetrate the icy fields which abound in these seas, in search of this imaginary continent, but without success, he having penetrated no farther than 72°. See COOK'S Discoveries, N^o 49. and 71.

Within the polar circles the sun does not always rise or set every 24 hours as in the other zones; but for a certain number of days in summer he never sets, and for a certain number of days in winter he never rises; the number of days during which the sun is present or absent increasing from the polar circles to the poles, so that at the poles he never sets for six months, nor rises during a like period.

82 Periscii. When the sun continues above the horizon more than 24 hours, the inhabitants of the polar regions have their shadows cast all around them; and hence they have been called Periscii. See PERISCII.

83 Climates. The ancients did not employ regular parallels of latitude, but they divided the spaces between the equator and the poles into small zones corresponding to the length of the longest day in each division. To these subdivisions they gave the name of climates, the situation and extent of which they determined in the following manner. As the day at the equator is exactly 12 hours throughout the year, but the longest day increases as we approach the poles, the ancients made the first climate to end at that latitude where the longest day was 12½ hours, which by observation they found to be in the latitude of 8° 25'. The second climate extended to latitude 16° 25', where the longest day is 13 hours, and thus a new climate extended, so as to divide the whole tract between the equator and the poles into 24 climates, in each of which the longest day was longer by half an hour than in that nearer the equator. The space between the polar circles and the poles they divided into six climates, in each of which the length of the longest day increased by a month, till at the poles it was six months long. Hence, the 24 climates between the equator and the polar circles are called Hour Climates; and the six between the polar circles and the poles are called Month Climates. For further particulars respecting this ancient division of the globe, and a table of the climates by Ricciolus, see CLIMATE. As the table given under that article is calculated only for the middle of each climate, and neither mentions the breadth of each, nor is extended to all the climates, we shall here subjoin one in which are given the latitude at which each climate terminates, its breadth in degrees, and the length of the longest day at the parallel terminating each.

84 Table of climates. HOUR CLIMATES.

85 As the division of the globe into climates, though Places in now almost disused, is of service in shewing the length the north- of the longest day in different countries, we shall here enumerate the principal places in each northern climate, these being best known and most interesting.

I. The Gold and Silver Coasts in Africa; Malacca in the East Indies; and Cayenne and Surinam in South America.

II. Abyssinia in Africa; Siam, Madras, and Pondicherry, in the East Indies; the isthmus of Darien; Tobago, the Grenades, St Vincent, and Barbadoes, in the West Indies.

III. Mecca in Arabia; Bombay, part of Bengal, in the East Indies; Canton in China; Mexico and the bay of Campeachy, in North America; and Jamaica, Hispaniola, St Christopher's, Antigua, Martinique, and Guadeloupe, in the West Indies.

IV. Egypt and the Canaries in Africa; Delhi, the capital of the Mogul empire, in Asia; most of the gulf of Mexico, and East Florida, in North America; and the Havannah in the West Indies.

V. Gibraltar; part of the Mediterranean sea; the Barbary coast in Africa; Jerusalem, Isfahan, capital of Persia, and Nankin, in China, in Asia; and California, New Mexico, West Florida, Georgia, and the Carolinas in North America.

VI. In Europe, Lisbon, Madrid, the islands of Minorca and Sardinia, and part of Greece or the Morea; in Asia, Asia Minor, part of the Caspian sea, Samarcand, Pekin, Corea, and Japan; and in North America, Maryland, Philadelphia, and Williamiburgh in Virginia.

VII. In Europe, the northern provinces of Spain, the southern provinces of France, Turin, Genoa, Rome, and Constantinople; in Asia, the rest of the Caspian, and part of Tartary; and in North America, Boston and New York.

VIII. Paris and Vienna, in Europe; and New Scotland, Newfoundland, and Canada, in North America.

IX. London, Flanders, Prague, Dresden, Cracow, in Europe; the southern provinces of Russia and the middle of Tartary in Asia; and the northern part of Newfoundland, in America.

X. Dublin, York, Holland, Hanover, Warsaw; the west of Tartary, Labrador, and New South Wales, in North America.

XI. Newcastle, Edinburgh, Copenhagen, and Moscow.

XII. Southern part of Sweden; and Tobolsk in Siberia.

XIII. Stockholm; and the Orkney isles.

XIV. Bergen in Norway, and St Peteriburgh.

XV. Hudson's straits in North America.

XVI. Most of Siberia; and the southern part of Greenland.

XVII. Drontheim in Norway.

XVIII. Part of Finland in the Russian empire.

XIX. Archangel on the White sea.

XX. Iceland.

XXI. Northern parts of Russia in Europe, and Siberia in Asia.

XXII. New North Wales, in North America.

XXIII. Davis's straits, in North America.

XXIV. Samoieda in Asia.

XXV. Northern parts of Lapland.

XXVI. West Greenland.

XXVII. Southern part of Nova Zembla.

XXVIII. Northern part of Nova Zembla.

XXIX. Spitzbergen.

XXX. Unknown.

The only parts of the terrestrial globe that we have yet to describe and illustrate are the Quadrant of Altitude, and the Wooden Horizon; and these it is necessary

to explain, before we proceed to consider the remaining problems performed with this globe.

The Quadrant of Altitude is a thin flexible slip of brass, graduated into 90°, and made to fix on any part of the brazen meridian by means of a nut and screw. Round this nut it moves on a pivot, and by its flexibility may be applied close to the surface of the globe. The quadrant of altitude is used to measure the distances of places from each other on the terrestrial globe, and to ascertain the altitudes of the sun, stars, &c. on the celestial globe.

To measure the distance between two places on the globe, nothing more is required than to stretch the graduated edge of the quadrant between them, and mark the number of degrees intercepted. These reduced to geographical, or to English miles (by N° 63.) give the absolute distance between the places. It is most convenient to bring one of the places to the zenith, which may be done by rectifying the globe for the latitude of that place as immediately to be explained, and then to stretch the quadrant to the other place, the distance marked, subtracted from 90°, gives the true distance in degrees. If the distance required be greater than 90°, it is proper to rectify the globe for the antipodes of the given places, and add the distance observed to 90°: the sum is the distance required.

It has been very generally stated that the bearing of one of the places from the other may be found by observing, on the wooden horizon, in what point of the compass the quadrant of altitude thus fixed in the zenith, cuts the horizon. This is considered by Mr Pattefon as a mistake: "For (says he) supposing one of the places to lie due east of the other, they are in the same parallel of latitude, and consequently it is impossible that the prime vertical of either of them (that is, a circle cutting the east and west points of the horizon, should pass through the other, unless they both lay under the equator. A line shewing the bearings of places is called a rhumb line. The lines of north and south on the globe, being meridians, and those of east and west, being parallels of latitude, are consequently circles; but all the remaining rhumbs are a kind of spiral lines."

The globes are supported by a wooden frame ending above in a broad flat margin, on which is pasted a pa. Wooden horizon. marked with several graduated circles. This broad margin is called the wooden horizon, and represents the rational horizon of the earth, or the limit between the visible and the invisible hemispheres. On the paper with which the wooden horizon is covered, are drawn four concentric circles. The innermost of these is divided into 360 degrees, divided into four quadrants. The second circle is marked with the points of the compass, i. e. the four cardinal points, east, west, north, and south, (d) each being subdivided into eight parts or rhumbs, (see COMPASS.) The circle next to that just mentioned contains the twelve signs of the zodiac, distinguished by their proper names and characters; and

(d) The cardinal points of the compass are thus determined. The two points in which the meridian of any place when produced so as to pass through the nearest pole, cuts the horizon, (using this in an astronomical sense, see ASTRONOMY,) are the north and south points; the former being that point where the meridian first cuts the horizon in the northern hemisphere, and the south, that where it first meets the horizon in the southern hemisphere. Again, the two points where a great circle, passing through the zenith at right angles with the meridian, (and called

and each sign is divided into 30 degrees. The last circle shows the months and days corresponding to each sign.

This wooden ring can represent the rational horizon of any place marked on the terrestrial globe only, when that place is situated in the zenith; and the method of bringing the place into this situation is called rectifying the globe.

PROBLEM VIII. To rectify the globe according to the latitude of any place.

Find the latitude of the place, (by Problem I.) and see whether it be north or south. Then elevate the pole of the globe which is in the same hemisphere with the latitude, as far above the wooden horizon as is equal to the latitude; bring the given place to the brazen meridian, and it will be in the zenith.

Example. To rectify the globe for the latitude of Edinburgh. The latitude of Edinburgh is $55^\{\backslash circ\}\; 58\text{'}$ N. therefore raise the north pole $55^\{\backslash circ\}\; 58\text{'}$ above the horizon, and bring Edinburgh below the brazen meridian.

It is for the purpose of more easily rectifying the globe, that one half of the brazen meridian is graduated from the poles to the equator; as, where this is not done, it is necessary to take the complement of the latitude, or the difference between it and $90^\{\backslash circ\}$, which in some cases requires a calculation.

The place being brought below the meridian, when the pole is elevated to the proper degree, it is evidently in the zenith, or $90^\{\backslash circ\}$ distant every way from the horizon. Thus, in the above example, if we count the degrees from that part of the meridian below which Edinburgh is situated, we shall find that they amount to $90^\{\backslash circ\}$ each way; for counting from Edinburgh along the meridian to the north pole, we have $34^\{\backslash circ\}\; 2\text{'}$; which added to $55^\{\backslash circ\}\; 58\text{'}$ the elevation of the poles gives $90^\{\backslash circ\}$ on that side. Again, counting from the same point of the meridian towards the southern part of the horizon, we have $55^\{\backslash circ\}\; 58\text{'}$, as far as the equator, and $34^\{\backslash circ\}\; 2\text{'}$ from thence to the horizon, making, as before, $90^\{\backslash circ\}$, and as the graduated edge of the meridian is $90^\{\backslash circ\}$ both from the eastern and western side of the horizon, Edinburgh, in this situation of the globe, is in the zenith.

When either of the poles of the globe is thus elevated above the horizon, so as not to be in the zenith, the globe is said to be in the position of an oblique sphere, in which the equator and all its parallels are unequally divided by the horizon. This is the most common situation of the earth, or it is the situation which it has with respect to all its inhabitants, except those at the equator and the poles. To the inhabitants of an oblique sphere the pole of their hemisphere is elevated above the horizon as many degrees as are equal to their latitude, and the opposite pole is depressed as much below the horizon, so that the stars only at the former are seen; the sun and all the heavenly bodies rise and set obliquely, the seasons are variable, and the days and nights unequal. This position of the sphere is represented at fig. 6. where the equator EQ, and the paral-

lels cut the horizon HO obliquely, and the axis PS is inclined to it. Hence this position is called oblique.

If the globe is placed in such a position that any point of the equator is in the zenith, it is said to be in the position of a right or direct sphere, because the equator and its parallels are vertical, or over the horizon at right angles. This position is seen at fig. 7. where the axis PS is in the plane of the horizon, and the equator EQ is in a plane perpendicular to it. The inhabitants of such a sphere, which are the inhabitants of the earth below the line, have no elevation of the poles, and consequently no latitude: they can see the stars at both poles; all the stars rise, culminate, and set to them; and the sun always moves in a curve at right angles to their horizon, and is an equal number of hours above and below it, making the days and nights always equal.

If the globe be so placed that one of the poles is in Parallel the zenith, and consequently the other in the nadir, it sphere. is in the position of a parallel sphere; so called because the equator EQ (fig. 8.) coincides with the horizon, and the parallels are of course parallel to it; while all the meridians cut the horizon at right angles. The inhabitants of a sphere, in this position, have the greatest possible latitude; the stars, which are situated in the hemisphere to which the inhabitants belong, never set, but describe circles all around; while those of the contrary hemisphere never rise: the sun is above the horizon for six months, during which it is day, and is, below the horizon for an equal interval, when it is night.

The wooden horizon is a necessary part of the apparatus of both globes; but it has been shewn, that in the terrestrial globe, it can represent the rational horizon of a place, only when the globe is rectified for the latitude of that place. In the celestial globe, it represents the rational horizon in all positions.

In Adams's globes there is a thin brazen semicircle NHS (fig. 5.) that is moveable about the poles, and has a small thin circle N sliding on it. This semicircle is graduated into two quadrants, the degrees of which are marked both ways from the equator to the poles in the terrestrial globe: this semicircle represents a moveable meridian; and the small sliding circle, which is marked with a few of the points of the compass, is called a visible horizon, the use of which will appear presently.

Before we proceed to the remaining problems on the terrestrial globe, it will be proper to take notice of some geographical principles that are connected with the horizon.

It is evident, that the extent of the sensible horizon of an observer depends on the height of his eye above the level surface of the earth. An eye placed on the surface of the earth sees scarcely any thing around it; but if it is elevated above that surface, it sees farther in proportion to its elevation, provided always that its view is not obstructed by intervening objects. Thus, in an extensive plain, the eye can see farther, if elevated to

called the prime vertical) cuts the horizon, are the east and west points; the former being on the left hand of a person facing the sun at noonday, while the latter is on his right hand.

Principles and Practice. to a proper height, than it can from the same height in a town or among hills; and, at sea, where the surface is perfectly equal, the view is in proportion to the height of the eye. It becomes an interesting problem to ascertain the extent of the visible horizon, or the distance to which a person can see at any given height of the eye; as, when this is known, we can calculate pretty accurately the distance of an object seen from such a height, as land seen from the topmast of a ship at sea.

For solving this problem, it must be remarked, that the distance of an observer from the boundary of the horizon, or from a distant object, is different when measured along the surface of the earth, and when measured in a direct line. To illustrate this, let HDN (fig. 9.) represent a section of the earth, of which C is the centre, and let D be the situation of an observer, whose eye is elevated to B. The lines BA, BE, tangents to the curve at H and E, represent the limit of the visible horizon, or the radius of the circle circumscribing vision. If the eye were elevated still higher, as to G, it is evident, that the extent of the visible horizon will be increased, being now represented by the tangent GF. The length of the tangent BA, or GF, is easily found by plane trigonometry (x).

93. Horizon of the sea. It was remarked above, that the visible horizon is most distinct at sea, from the absence of those objects which obstruct vision on land. Hence the sensible horizon is sometimes called the horizon of the sea, and this may be observed by looking through the sights of a quadrant at the most distant part of the sea. In making this observation, the visual rays BA, or GF, by reason of the spherical surface of the sea, always extend a little below the true sensible horizon SS, and consequently below the rational horizon HN, which is parallel to it. Hence the quadrant shows the depression of the horizon of the sea lower than it really is; and it is obvious from the figure, that the higher the eye is situated, the greater must be this depression. Thus, the depression, when the eye is at G, marked by GF, is evidently much greater than that marked by BE, when the eye is at B. The depression of the horizon of the sea is not always the same, though there be no variation in the height of the eye; but the difference in this case

is very small, amounting only to a few seconds, and is owing to a difference of the degree of refraction in the atmosphere. Were there no refraction, the visual ray would be BE (when the eye is at B), and E would be the most distant point; but, by reason of the refraction, a point on the surface of the earth beyond E, as F, may be seen by an eye situated no higher than B; and if the refraction were still greater, a still more distant point might be observed.

94. Difference between the apparent and true level. It will be necessary here to anticipate a few remarks respecting the difference between the apparent and true levels; a subject that will be more fully discussed under LEVELLING. Two or more places are on a true level, when they are equally distant from the centre of the earth, and one place is higher than another, or above the true level, when it is farther from the centre of the earth. A line that is equally distant in all its points from the centre, is called the line of true level, and it is evident that this line must be curved; and either make part of the earth's surface, or be concentrical with it. Thus the line DAO, which has all its points, D, A, O, equally distant from the centre C, is the line of true level. But the line of sight DMP, as given by the operation of a level, is a straight line, which is a tangent to the earth's surface at D, always rising higher above the true line of level, according as it extends to a greater distance. This straight line is called the line of apparent level. Thus MA is the height of the apparent level above the true at the distance DA, and OP is the excess of the apparent above the true level, at the distance DO.

The following table was constructed by Cassini, for the purpose of shewing the excess of the apparent above the true level at various distances from the point of observation. It consists of three columns, in the first of which the distance of the observed object from the place of observation is given, from one second to 60 minutes, or a degree. In the second is given the length of the arc measured on a great circle of the earth, that corresponds to the observed distance, in feet and inches; and in the third is given the height of the apparent above the true level in feet and inches, corresponding to each observed and real distance of the object.

(x) In the right-angled triangle ACB (fig. 9.), the length of CB is given, supposing the height of the eye BD to be 6 feet; for adding 6 feet to 19,943,400 feet, the length of the semidiameter of the earth, we have 19,943,406 feet for the length of BC. Then, making the hypotenuse CB radius, we shall have, As radius to the line of the angle BCA, so is CB to BA; and this will be nearly the same as the arc DA. Again, without finding the quantity of the angle at C, BA may be found, by considering that BA² is equal to the difference of the squares of CB and CA, i. e. BA² = CB² - CA² = (CB + CA) × (CB - CA) = CB + CA into BD; and hence BA = √(CB + CA) × BD.

To illustrate the last in numbers, we have CB = 19,943,406 feet, and CA = 19,943,400 feet. Then, to find BA, we have 19,943,406 + 19,943,400 (= 39,886,806) × 19,943,406 - 19,943,400 (= 6) = 239,320,836; whence BA = √239,320,836 = 15470 feet nearly, or about three miles.

The distance, to which a person can see, is found to vary as the square root of the altitude of the eye. To find a general expression for this quantity,

let $a$ be the altitude of the eye in feet,
$d$ the distance at that altitude in miles;

then we have $\backslash sqrt\{6\}\; :\; \backslash sqrt\{a\}\; =\; 3\; :\; d\; =\; \backslash frac\{3\}\{\backslash sqrt\{6\}\}\; \backslash times\; \backslash sqrt\{a\}\; =\; 1.2247\; \backslash times\; \backslash sqrt\{a\}$. Hence, we deduce this general rule: Multiply the square root of the height of the eye in feet by 1.2247, and the product will be the distance to which we can see from

from that height in miles. Example. Let the height of the eye be 49 feet. Multiply the square root of 49 or 7, by 1.2247, and we have 8.5729 or about 8½ miles for the distance to which the eye can see at the height of 49 feet.

The above table will answer several useful purposes. In the first place, the height of the apparent level above the true may be found by it at any distance, from one second to one degree, or 69 $\backslash frac\{1\}\{2\}$ miles. Thus, at the distance of 30'—about 35 miles, we have 182820 feet for the length of the arc of a great circle on the earth, and corresponding to this we have 797 feet 8 inches 484 parts for the excess of the apparent level above the true. 2. The extent of the visible horizon corresponding to any height of the eye, may be found from the table by observation. The semidiameter of the horizon does not sensibly differ from an arc of a great circle on the earth, containing as many minutes and seconds as are equal to the angle of depression observed, and the number of feet contained in such an arc may be found in the table. Thus, if the depression, as observed by observation, be 40", its semidiameter is also about 40", and the length of the arc corresponding to it is 243,760 feet.

The following table, also taken from Cassini, shows the different depressions of the horizon of the sea at different heights of the eye, both by observation and calculation; with the difference betwixt the two occasioned by refraction.

In the above table, the depression, as estimated by calculation, is greater than that by observation in every case except the last, in which the latter is greater by two seconds than the former; but this difference was too small to be discovered by the instrument that Cassini employed.

Refraction lessens the angle of depression, by raising the objects observed; but as this refraction is itself variable, the depression and extent of the horizon also vary. We are informed by Cassini, that even in the finest weather he observed the refraction to differ at the same hour of different days, and at different hours of the same day. The truth of this observation may be easily ascertained by looking through a telescope furnished with cross hairs, and fixed in such a position that some highly elevated object, as the weathercock of a steeple, may be seen through it; for, on observing the weathercock at different times of the day, it will be seen sometimes on the centre of the object-glass; sometimes above, and sometimes below it. A similar experiment may also be made with plane sights fixed on a cross-staff. It has long been observed, that the top of a distant hill may sometimes, when the refraction is very great, be distinctly seen from a situation from which, at other times, when the refraction is much less, it is not discernible, even though the sky be very clear.

Many of the following problems may seem to belong to the celestial rather than the terrestrial globe; but as they may be solved equally well by means of both, and as persons not uncommonly possess a terrestrial globe without its usual companion, we shall throw as many problems as possible under this head.

PROBLEM IX. To find the sun's place in the ecliptic for Problems 95 respecting the sun.

Find the day of the month in the calendar on the wooden horizon; and opposite to it, in the adjoining circle, will be found the sign and degree in which the sun

From the above, it is easy to deduce the method of computing the distance of any object seen in the horizon from a certain height. Thus, suppose a man at the mast-head, 130 feet above the water, sees land or a ship just coming in sight. We know, that, at this height, an eye can see 14 miles, consequently the object seen will be about 14 miles or about five leagues distant. If the object is within the horizon, or nearer the place of observation, its distance may be calculated pretty exactly, by descending from the mast-head till the object just comes to the horizon; measuring the height at which this takes place, and thence computing the distance.

sun is on the given day. Then look for the same sign and degree in the circle of the ecliptic drawn on the globe, and that is the sun's place at noon for the given time.

Ex. 1. What is the sun's place on the 4th of June?
Ans. In $13^\{\backslash circ\}\; 57\text{'}$ of the sign Gemini.

Ex. 2. Required the sun's place for the first day of every calendar month?

PROBLEM X. To find the sun's declination for any given time.

Find the sun's place for the given day by Prob. X. and bring it to the brazen meridian. The degree marked on the meridian immediately over the place is the declination required.

Ex. Required the sun's declination for 18th March? The sun's place for the given day is $20^\{\backslash circ\}\; 7\text{'}$ of $\backslash kappa$, and this being brought to the meridian, will be immediately below $3^\{\backslash circ\}\; 54\text{'}$ S. which is therefore the declination required.

From the above example, it is evident that the method of finding the declination of the sun corresponds to that of finding the latitude of a place on the globe, given in Problem I. the sun's declination being measured in the same way by an arc of the meridian interposed between the equator and the sun's place in the ecliptic (F).

PROBLEM XI. To rectify the globe for the sun's place and the day of the month.

Find the sun's declination for the given day, by Problem XI.; then elevate the pole that is in the same hemisphere with the degree of declination, as many degrees as are equal to the declination.

Ex. Rectify the globe for the sun's place on the 6th October? Ans. The sun's declination on that day is $5^\{\backslash circ\}$ S. therefore the south pole must be elevated $5^\{\backslash circ\}$ above the horizon.

Rectifying the globe for the sun's declination corresponds to the rectifying of it for the latitude of a given place. See N^o 88.

PROBLEM XII. To find the time of the sun's rising and setting at a given place, for any given day.

Rectify the globe for the declination on the given day, and bring the given place to the meridian, and set the index of the hour circle at XII. Turn the globe, till the given place come to the eastern edge of the horizon, and the time of sunrise will be shewn by the position of the index. Then turn the globe till the given place come to the western part of the horizon, and the position of the index will point out the time of sunset.

To perform the same problem by Adams's globes. Rectify the globe for the declination, bring the given place to the meridian, and set the horary index at 12 as before; then turn the globe towards the west, till the given place reach the western edge of the horizon, and the index will point to the time of sunrise. The time of sunset will be known, in like manner, by bringing the place to the eastern side of the horizon.

If the hour circle in the ordinary globes has a double row of figures, the sun's rising and setting may be found at the same time; for if the place be brought to the eastern part of the horizon, the time of sunrise will be shewn by the index, in that circle where the hours increase towards the east; and the time cut by the index in the circle where the hours increase towards the west, will show the time of sunset.

Ex. 1. Required the time of the sun's rising and setting at London, on the 29th August? Ans. The sun rises at nine minutes after five, and sets nine minutes before seven.

Ex. 2. Required the time of sunrise and sunset at Edinburgh on the 1st of June? Ans. For sunrise, 27 minutes after three; for sunset, 33 minutes after eight.

COROLLARY. From this problem we may easily find the length of the day and night for any given time; for, having found by the globe the time of sunrise and sunset, the double of the latter is the length of the day, and the double of the former the length of the night.

PROBLEM XIII. To find the sun's meridian altitude on any given day, at a given place.

Rectify the globe for the latitude of the given place, by Problem VIII.; find the sun's place on the given day by Problem IX. and bring it to the brazen meridian. Then fix the quadrant of altitude in the zenith, or over the given place, and bring it over the sun's place; and the degree of the quadrant lying over the sun's place will shew the meridian altitude.

If the globe has no quadrant of altitude, the sun's meridian altitude may be found by counting the number of degrees on the meridian, between the horizon and the sun's place.

Ex. Required the sun's meridian altitude at Edinburgh on the 21st of June? Ans. $57^\{\backslash circ\}\; 30\text{'}$, or the greatest possible, this being the summer solstice.

COROLLARY. It may be known whether the sun's meridian altitude be north or south, by the following observations. When the sun's declination and the latitude of the place are of different names, i. e. the one north and the other south, the meridian altitude is of the same name with the declination. If the declination and latitude be both north or both south, the altitude is of the same name with the declination, if the latter be the greater; but, otherwise, the altitude is of an opposite name.

PROBLEM XIV. Having the latitude of the place and the day of the month given, to find the sun's altitude for any given hour.

Rectify the globe for the latitude; find the sun's place, and bring it to the meridian, and set the horary index

Principles and Practice. index to noon; turn the globe till the index point to the given hour, then fix the quadrant of altitude in the zenith, and bring its graduated edge over the sun's place, and the degree cut by the sun's place will be the altitude required.

Ex. What will be the sun's altitude at 10 o'clock A. M. on the 30th of November at Edinburgh? Ans. $8^\{\backslash circ\}\; 50\text{'}$.

PROBLEM XV. Having the sun's meridian altitude given at any place, to find the latitude of the place.

Bring the sun's place for the given day to the meridian, and move the globe in the horizon till the distance between the sun's place and the northern or southern edge of the horizon, (according as the case may require), be equal to the given altitude. The degree of elevation of the pole will shew the latitude required.

Ex. The sun's meridian altitude observed at a certain place on 5th August is $74^\{\backslash circ\}\; 24\text{'}\; N$. What is the latitude of the place? Ans. $1^\{\backslash circ\}\; 36\text{'}\; N$.

PROBLEM XVI. The latitude of the place and the day of the month being given, to find when the sun is due east or due west.

Rectify the globe for the latitude of the place, bring the sun's place to the meridian, and set the index to XII. Fix the quadrant of altitude in the zenith, and if the sun's declination be of the same name with the latitude, bring the graduated edge of the quadrant to the eastern side of the horizon; but if the declination is of a different name from the latitude, bring the quadrant to the western part of the horizon. Turn the globe till the sun's place in the ecliptic come below the edge of the quadrant, and the index will point to the hour when the sun is due east. Subtract this from XII, and the remainder shews the time when the sun is due west.

Ex. At what hours is the sun due east and west at the summer and winter solstice at Greenwich? Ans. At the summer solstice he is due east at 20 minutes past seven, and due west at 20 minutes before five. At the winter solstice he is due east at 20 minutes before five, and due west at 20 minutes past seven.

COROLLARY. When the declination and latitude are of the same name, the sun is due east after rising; but when the declination and latitude are of different names, he is due east before rising. As it is not convenient to observe on the globe when the sun is due east before rising, or while he is under the horizon, it is better to bring the opposite point of the ecliptic due west, and then the index shews the time when he is due east.

PROBLEM XVII. Having a place in the torrid zone given, to find on what two days of the year the sun is vertical at that place.

Find the latitude of the given place, and keeping that in view, turn the globe round, noting the two points at the ecliptic that pass below the degree of latitude. Find in the calendar circle of the horizon the days corresponding to those points of the ecliptic; and these are the days on which the sun is vertical at the given place.

Ex. 1. On what days is the sun vertical at St He-

lena, in latitude $15^\{\backslash circ\}\; 55\text{'}\; S$? Ans. On 6th February and 6th November.

Ex. 2. Required the days on which the sun is vertical at Tobago, in latitude $11^\{\backslash circ\}\; 29\text{'}\; N$? Ans. On April 19. and August 23.

PROBLEM XVIII. To find those places in the torrid zone where the sun is vertical on a given day.

Find the sun's place for the given day, and bring it to the brazen meridian; then turn the globe, and note all the places which pass under that point of the meridian: these will be the places to which the sun is vertical on the given day.

Ex. 1. In what places is the sun vertical at the summer solstice? Ans. At Canton in China, at Calcutta in Bengal, at Mecca in Arabia, and at the Havana.

Ex. 2. To what places is the sun vertical on the 16th of May and 29th of July? Ans. At Bombay, Pegu, in the northern part of Manila, in the middle of the Ladronne islands, at Owhyhee, Mexico, in Hispaniola, and at Tombuctoo in the central parts of Africa.

PROBLEM XIX. Having the day and hour at any given place, to find where the sun is then vertical.

Find the sun's declination by Problem XI, and the places where it is noon at the given time, by Problem III; then any of those places where it is noon, whose latitude is the same as the sun's declination, will have the sun vertical at the given time.

Ex. On the 1st of August at Edinburgh, it being 35 minutes past four, P. M. it is required to find where the sun is vertical? Ans. The sun's declination on that day is $18^\{\backslash circ\}\; 14\text{'}\; N$, and the place where it is noon at the given time, that lies nearest in latitude to the declination, is Kingston in Jamaica: this, therefore, is the place required.

PROBLEM XX. A place in the northern frigid zone being given, to find when the sun begins to appear above the horizon, and when to disappear; as also the length of the longest day and night.

Rectify the globe for the latitude, and bring the ascending signs of the zodiac (see ASTRONOMY, No 52) to the southern part of the horizon; observe what degree of the ecliptic is intersected by that point of the horizon, and in the calendar circle find the day of the month answering to that degree. That will shew the time of the sun's first appearance above the horizon at the given place, and this is the end of the longest night in that latitude. Then bring the descending signs to the same part of the horizon, and observe the day which answers to the degree of the ecliptic intersected; this will shew the time of the sun's disappearance, or the beginning of the longest night. Now bring the ascending signs to the northern part of the horizon, and observe the degree of the ecliptic, and the corresponding day as before, which will give the time when the sun begins to shine continually, or the beginning of the longest day. Again, bring the descending signs to the same point, and thus will be given the time when the sun ceases to shine continually, or the end of the longest day.

Ex. At what time does the sun begin to appear above

above the horizon at North Cape in Lapland, the latitude of which is $72^\{\backslash circ\}$ N. ? When does he disappear, and how long is he entirely absent during the longest night? Ans. He begins to appear on the 26th of January, and entirely disappears on the 16th of November; he is therefore absent for 71 days.

COR. From the sun's first appearance at the end of the longest night to the beginning of the longest day, and from the end of the longest day to the sun's total disappearance at the beginning of the longest night, he rises and sets every day.

PROBLEM XXI. To find in what part of the northern frigid zone the sun begins to shine continually on a given day.

Find the sun's declination for the given day, and subtract this from $90^\{\backslash circ\}$, the remainder will shew the latitude required.

Note.—The given day must be between the 21st of March and the 21st of June, as at no other time does the sun begin to shine continually in the northern frigid zone.

Ex. Required the latitude in which the sun begins to shine without setting on the 1st of June? Ans. The sun's declination for that day is $22^\{\backslash circ\}$ N. and this subtracted from $90^\{\backslash circ\}$ leaves $68^\{\backslash circ\}$ N. the latitude required.

PROBLEM XXII. The length of the longest day in any place being given, to find the latitude of that place.

Bring the first degree of Cancer to the meridian, and set the horary index at noon. Then turn the globe towards the west, till the index point to the hour of sunset, or half of the length of the given day; raise or depress the pole, till the sun's place in the ecliptic is exactly in the western edge of the horizon. The elevation thus obtained will be equal to the required latitude.

In Adams's globes, after bringing the first degree of Cancer to the meridian, and setting the index to noon, the globe must be turned towards the west, till the index shew the time of sunset, and the sun's place must be brought to the eastern side of the horizon.

Ex. In what latitude is the longest day 18 hours long? Ans. In latitude $58^\{\backslash circ\}\; 30\text{'}\; \backslash text\{\; N.\}$

By this problem the limits of the hour climates may be pretty nearly ascertained.

PROBLEM XXIII. To find the latitudes of those places in the frigid zone where the sun is continually above the horizon for a given number of days.

Count from the first degree of Cancer towards the nearest equinoctial point, as many degrees as is equal to half the given number of days; bring the point thus obtained below the meridian, and note the degree of the meridian which it intersects. This subtracted from $90^\{\backslash circ\}$ will leave a remainder that is nearly equal to the latitude of the place.

Ex. In what latitude does the sun never set during 76 days? Ans. In latitude $71^\{\backslash circ\}\; 30\text{'}$, or very near the southern part of Nova Zembla.

Note.—This problem cannot be performed accurately by the globe; for as the sun requires 365 days six hours to move through the whole $360^\{\backslash circ\}$ of the ecliptic, he does not advance quite a degree in 24 hours.

By this problem the limits of the month climates may be pretty nearly ascertained.

PROBLEM XXIV. The hour and day being given at any place, to find in what places the sun is rising, and in what he is setting; where it is noon, and where midnight.

Find by Problem XIX. the place to which the sun is vertical at the given time; rectify the globe for the latitude of that place, and bring the place below the meridian. In this position of the globe all those places that lie within the western edge of the horizon will have the sun rising, and all those which are in the eastern edge of the horizon will have it setting. Again, to those places which lie under the upper semicircle of the brazen meridian, it will be noon; and to those which lie below the lower semicircle, it will be midnight.

Ex. Suppose it to be four o'clock P. M. on the 4th of June at London; where is the sun at that time rising, and where is he setting; to what places is it noon, and to what midnight? Ans. The north-eastern part of Siberia, Kamtschatka, the most western of the Sandwich isles, and the most eastern of the Society isles, are within the western edge of the horizon, and consequently to these the sun is rising. At Tobolisk, in the Caspian sea, in the desert of Arabia, in the middle of the Red sea, in Abyssinia, in the central parts of Africa, and in the country of the Hottentots, the sun will be setting, as these places lie within the eastern edge of the horizon. New Britain, the islands of Martinique and Trinidad, and the middle part of South America, which lie below the upper semicircle of the meridian, have noon; and Chinese Tartary, the eastern part of China, the Philippine isles, and the western part of New Holland, which are situated below the under edge of the semicircle, have midnight.

As the remaining problems on the terrestrial globe chiefly respect the continuance of twilight, it is proper, before we proceed, to make a few remarks on this subject. For the explanation of the term, see CREPUSCULUM and TWILIGHT.

The Crepusculum, or Twilight, it is supposed, usually begins and ends when the sun is about $18^\{\backslash circ\}$ below the horizon; for then the stars of the 6th magnitude disappear in the morning, and appear in the evening. It is of longer duration in the solstices than in the equinoxes, and longer in an oblique sphere than in a right one; because in those cases the sun, by the obliquity of his path, is longer in ascending through $18^\{\backslash circ\}$ of latitude.

Twilight is occasioned by the sun's rays refracted in our atmosphere, and reflected from the particles of it to the eye. For let A (fig. 10.) be the place of an observer on the earth ADL, AB the sensible horizon, meeting in B the circle CBM bounding that part of the atmosphere which is capable of refracting and reflecting light to the eye. It is plain that when the sun is under this horizon, no direct rays can come to the eye at A: but the sun being in the refracted line CG, the particle C will be illuminated by the direct rays of the sun; and that particle may reflect those rays to A, where they enter the eye of the spectator. And thus the sun's light illuminating an innumerable multitude of particles, may be all reflected to the spectator at A.

Principles and Practice. A. From B draw BD touching the circle ADL in D, and let the sun be at S in the line AD; then the ray SB will be reflected into the situation BA, and will enter the eye, because from a principle in optics the angle of incidence DRC is equal to the angle of reflection ABE. See Optics. This ray SB, or BA, will therefore be the first that reaches the eye at dawn in the morning, and the last that falls on the eye at night, when twilight ceases, because as the sun gets lower down, the particles of the air at B will no longer be illuminated.

The depth of the sun below the horizon at the beginning of the morning or end of the evening twilight, is determined by observing the moment when the air first begins to shine in the morning, or ceases to shine in the evening; then finding the sun's place for that time, and hence the time till his rising in the horizon, or after his disappearance below. This depth of the sun below the horizon has been variously stated by different astronomers, but it is now generally estimated at $18^\{\backslash circ\}$. Accordingly in Mr Adams's globes there is a circular wire fixed $18^\{\backslash circ\}$ below the horizon, to represent the limits of the crepusculum (see PWY, fig. 5.)

As the cause of twilight is not constant, its limits must continually vary; for if the exhalations in the atmosphere be more copious or more extensive than usual, the morning twilight will begin sooner, and that of the evening last longer than ordinary; as the more copious the exhalations, the more rays will be reflected from them, and consequently the more they will shine, and again, the higher they are, the sooner they will be illuminated by the sun. From this circumstance the evening twilight is commonly longer than the morning, at the same time, and in the same place. The refraction is also greater according as the air is more dense, and not only is the brightness of the atmosphere variable, but the same takes place in its height above the earth; therefore, the twilight is longest in hot weather, and in hot countries, all other things being equal. The chief differences, however, arise from the different situations of places on the earth, or from the difference of the sun's place in the heavens. Thus, the twilight is longest when the earth is the position of a parallel sphere, and shortest in that of a right sphere (see N^o 90.): and in an oblique sphere, the twilight continues longer at any place, in proportion as that place is nearer to either of the poles; a circumstance which affords considerable relief to the inhabitants of the northern countries in their long winter nights. Twilight continues longest in all places of north latitude, when the sun is in the tropic of Cancer, and to those in south latitude when he is in the tropic of Capricorn. The time of the shortest twilight also varies in different latitudes: thus, in England, the shortest twilight is about the beginning of October and of March, when the sun is in $\backslash alpha$ and $\backslash gamma$; hence, when the difference between the sun's declination and the depth of the equator is less than $18^\{\backslash circ\}$, so that the sun does not descend more than $18^\{\backslash circ\}$ below the horizon, the twilight will continue through the whole night, as happens in Britain from the 22d of May to the 22d of July.

In the latitude of $49^\{\backslash circ\}$ N. twilight continues for the whole night, only on the 21st of June, or the time of the summer solstice; but at all places further to the

north it continues for a certain number of days before and after the summer solstice. Principles and Practice.

Near the north pole there is continual twilight from the 22d of September, the time of the sun's permanent absence, to the 12th of November. It then ceases till about the 30th of January, when it again appears, and continues till the 21st of March, the time of the sun's permanent appearance. Hence the inhabitants of those places nearest the pole, though they never see the sun for nearly six months, have, however, the benefit of twilight for above the half of that time, and are entirely excluded from the sun's light little more than 12 weeks, during six of which the moon is constantly above the horizon.

Were it not for the gradual change from light to ⁹⁵Utes of darkness, and vice versa, which is the consequence of twilight, much inconvenience would arise. A sudden change from the darkness of midnight to the full splendor of the sun, and the reverse, would injure the sight, and would, in many cases, be productive of much danger to travellers, who would be overtaken by utter darkness before they had time to prepare for its approach.

PROBLEM XXV. To find where it is twilight at any ⁹⁹Problem respecting twilight. given time.

Find where the sun is vertical at the given time, and rectify the globe for the latitude of that place. Observe what places are within the limits of twilight, or not quite $18^\{\backslash circ\}$ below the horizon. To those which are situated within the western zone, between the horizon and the parallel of $18^\{\backslash circ\}$, it will be twilight in the morning; and those which are in the eastern zone will have it twilight in the evening.

This problem may be more conveniently performed by rectifying the globe for the antipodes of the place which has the sun then vertical, and observing what places are situated in the zone formed above the horizon, between it and a parallel circle of $18^\{\backslash circ\}$.

Ex. It is required to find where it is twilight on the 4th of June, when it is three o'clock, P. M. at London. Ans. Kamtchatka, the Sandwich isles, and the Marquesas, have twilight in the morning; and the inhabitants of Madagascar, of Tibet, and the eastern part of Persia, have twilight in the evening.

PROBLEM XXVI. To find the duration of twilight at a given place on any given day.

Rectify the globe for the latitude of the place; find the sun's place for the given day by Problem X. and bring it below the meridian, and let the horary index to XII. Turn the globe till the sun's place be just within the circle that marks the limit of twilight, and the index will shew the beginning of twilight. Subtract the time of the beginning of twilight from the time of sunrising at the given place (found by Problem XII.) and the remainder will shew the duration of twilight at the given place.

Note.—The above rule will answer both for the ordinary globes, and for those of Adams, except that in the latter the sun's place must be brought below the western part of the horizon. A more convenient way in both globes will be, to bring that point of the ecliptic which is opposite to the sun's place, $18^\{\backslash circ\}$ above the

the western horizon, and the index will then show the beginning of twilight.

Ex. How long will twilight continue at London on the following days: March 2d; September 25th; and December 26? Ans. On the 2d of March it will continue one hour and fifty minutes; on the 25th of September two hours; and on the 26th of December, two hours ten minutes (G).

PROBLEM XXVII. To show the cause of day and night by the globe.

It will have appeared, from the consideration of the cause of day and night given under the article ASTRONOMY, that only that half of the earth which is opposite to the sun, is illuminated by his rays, while that which is turned from him is involved in darkness. As the earth revolves on its axis from west to east, in the space of 24 hours, every place on the earth in the course of that time alternately enjoys the light of the sun, and is deprived of it.

To illustrate this by the globe, rectify the globe for the sun's declination, so as to place the sun in the zenith, and the horizon will represent the boundary between light and darkness; that hemisphere which is above the horizon being illuminated by the sun's rays, and that which is below the horizon being deprived of light. If now a patch is put on the globe, so as to represent any place, and if the globe be made to revolve from west to east; when the place is brought to the western edge of the horizon, the sun will appear to the inhabitants of that place to be rising in the east, though, in fact, the appearance arises from the place itself coming beyond the limit of darkness. As the globe continues to turn, the place rises towards the meridian, and this produces the appearance as if the sun were advancing towards the meridian in a contrary direction. When the place comes below the meridian, it is noon to that place, and the sun appears to have attained its greatest height.

As the place proceeds towards the east, it gradually recedes from the meridian, and the sun appears descending in the west. When it reaches the eastern edge of the horizon, and is proceeding below the boundary of light and darkness, the sun appears to be setting; and during the whole time that the place is moving below the horizon, the sun will not appear till the place once more rises in the west.

PROBLEM XXVIII. To find at what places an eclipse of the moon is visible at any given time.

Find the place to which the sun is vertical at the given time, and rectify the globe for the latitude of that place. As the moon is opposite to the sun, which illuminates the superior hemisphere of the globe, the

eclipse of the moon will be visible to all the places that lie below the horizon.

As the places below the horizon are not easily examined, this problem may be more conveniently performed by rectifying the globe for the antipodes of the place to which the sun is vertical at the given time, rather than for the place itself; as in this latter position of the globe the moon being in opposition to the sun, will be vertical to the place below the zenith, and its eclipse will be visible at all the places now above the horizon.

Ex. 1. On the 4th of January 1806, at 55 minutes past 11 P. M. reckoning the time at Greenwich, there was an eclipse of the moon. It is required to find those places to which the eclipse was visible? Ans. Through the greatest part of Africa, in some part of Europe, in Asia, South America, and a great part of North America.

Ex. 2. On the 10th of May 1808, when it is eight o'clock A. M. at Greenwich, the moon will be totally eclipsed. In what places will the eclipse be visible? Ans. In most parts of America; in the islands of the Pacific ocean, and on the eastern coast of New Holland.

SECT. II. Of the Use of the Celestial Globe.

THE celestial globe, with respect to the circles that are described on it, and the apparatus with which it is furnished, scarcely differs from the terrestrial globe, which has been so fully described in the preceding section. The surface of the celestial globe is made to represent all the stars that are commonly visible to the naked eye, arranged under their constellations, and bounded by the figures which have been given to these constellations by the early astronomers. (See fig. 5.) In Adams's celestial globe the moveable semicircle (No 91.) turning round the poles represents a circle of declination, and the small circle on it, an artificial sun or planet.

Both the globes are often furnished with a mariner's compass, which is usually placed in the lower part of the frame.

It must here be remarked, that the representation of the heavens on the celestial globe, though probably much more accurate than that of the earth on the terrestrial, is not so natural as the latter; for, in viewing the stars on the external surface of a globe, the spectator sees them in an opposite position to that in which he observes them in the heavens, so that to form a just conception of their exact situation, he must suppose his eye to be seated in the centre of the globe. Hence, if a large hollow hemisphere were made of glass, and if the stars in the corresponding hemisphere of the firmament were painted in transparent colours on its surface; an eye situated in the centre of such a hemisphere

(G) If we have the latitude of a place, and the sun's declination given, we may find the beginning of the morning and the end of the evening twilight by calculation. Thus, in the oblique-angled spherical triangle ZPN (fig. 11.) we have given ZP the co-latitude; PN the co-declination, and $ZN\; =\; 108^\backslash circ$ being the sum of $90^\backslash circ$ the quadrant, and $18^\backslash circ$ the depression at the extremity of twilight. Then by spherical trigonometry we may calculate the triangle ZPN, the hour angle from noon, and this reduced to time, at the rate of $15^\backslash circ$ per hour, gives the time from noon to the beginning or end of twilight. For the mode of calculation, see SPHERICS.

Principles and Practice. sphere would see the stars exactly as they appear in the heavens.

The great use of the celestial globe is to perform a variety of problems with respect to the stars, and the motions of the heavenly bodies through the space which they occupy.

PROBLEM I. To place the celestial globe in such a situation as that it shall exhibit an accurate representation of the face of the heavens at any given place, and at any given time.

Rectify the globe for the latitude of the place, as in Problem VIII. of the terrestrial globe, or by setting the pole of the celestial globe pointing to the pole of the earth, by means of the compass that is usually annexed to the globes; find the sun's place in the ecliptic; bring this to the meridian, and set the horary index at noon. Again, make the globe turn on its axis till the index point to the given time, and in this position the globe will exactly represent the face of the heavens, corresponding to the given time and place; every constellation and star in the heavens answering in position to those on the globe. Hence, by examining the globe, it will immediately be seen what stars are above or below the horizon, which are on the eastern and western parts of the heavens, which have just risen above the horizon, and which are about to sink below it.

As this problem will be found extremely useful to the student of astronomy, we shall here quote the example given in illustration of it by Messrs Bruce of Newcastle.

"Required the situation of the stars for the latitude of Newcastle, on October 6th, at eight o'clock in the evening?

"In our present survey of the heavens, we shall commence at the north point of the horizon, and proceed round eastward; noticing the different constellations, and the relative situation of the principal stars in these constellations.

"The first star which strikes the eye of the observer, in the north-east part of the heavens, is Capella, in the constellation Auriga, or the Waggoner: It is of the first magnitude, of the altitude of $23^\{\backslash circ\}$, or nearly the fourth part of the distance from the horizon to the zenith. There are two stars of the second magnitude, which form with Capella a triangle:—The star which forms the short side of the triangle is in the right shoulder of Auriga, and is marked $\backslash beta$; it lies at the distance of about $8^\{\backslash circ\}$ from Capella, further to the north; its altitude is $18^\{\backslash circ\}$:—The star forming the longer side of the triangle is in the Bull's northern horn; its distance from Capella is more than $26^\{\backslash circ\}$; its altitude not more than $5^\{\backslash circ\}$, and azimuth N. E. There are three stars of the fourth magnitude, a little to the south of Capella, that bear the name of the Kids.

"If a line be drawn through the two stars that form the upper side of the triangle, and continued to the horizon, it will point out Castor, $\backslash alpha$, in Gemini just rising, azimuth E. N. E.: it is between the first and second magnitude. The other stars in this constellation have not yet risen.

"A line drawn between Castor and Capella, and continued higher in the heavens, will point out Perseus, in which there are three stars, one of the second magni-

tude, $\backslash alpha$, named Algenib, and two of the third magnitude, one on each side of Algenib, at the distance of about $5^\{\backslash circ\}$: they form a line a little curved on the side next Auriga. The altitude of Algenib is $37^\{\backslash circ\}$; azimuth N. E. by E.

"A little to the south of Perseus is the Head of Medusa, which Perseus is holding in his hand. Besides two or three small stars, it contains one of the second, and one of the third magnitude. The name of the brightest is Algol; altitude $33^\{\backslash circ\}$, azimuth E. N. E. Algol is only $10^\{\backslash circ\}$ distant from Algenib.

"Directly below the Head of Medusa, about $14^\{\backslash circ\}$ above the horizon, are the Pleiades or seven stars: They are seated in the shoulder of Taurus, and are so easily known, that no description is necessary. Aldebaran, a star of the first magnitude, which forms the eye of Taurus, is just rising; azimuth E. N. E. A vertical circle drawn through Algol will point to it. There are two stars of the third magnitude, and several smaller very near Aldebaran, which form with it a triangle. The whole cluster is called the Hyades.

"A line drawn from Aldebaran through Algol, and continued to the zenith, will direct to Cassiopeia. This contains five stars of the third magnitude, besides several of the fourth: it is in form something like the letter Y, or, as some think, an inverted chair. It is situated above Perseus, within $30^\{\backslash circ\}$ of the zenith. The altitude of the brightest star, $\backslash alpha$, called Schedar, is $60^\{\backslash circ\}$; azimuth, E. N. E.

"Below Cassiopeia and west of Perseus is Andromeda, which contains three stars of the second magnitude. A line from Algenib, parallel to the horizon towards the south, will pass very near these three stars; and, as they are all of the same magnitude, and placed nearly at the same distance of $15^\{\backslash circ\}$ from each other, they may easily be known. The name of the star nearest Perseus, and which is in the foot of Andromeda, marked $\backslash gamma$, is Almaak: its altitude is $49^\{\backslash circ\}$; azimuth E. N. E. The name of $\backslash beta$, in the girdle, is Mirach: its altitude $44^\{\backslash circ\}$; azimuth E. The altitude of $\backslash alpha$, in the head of Andromeda, is $46^\{\backslash circ\}$; azimuth E. S. E.

"About $18^\{\backslash circ\}$ below Mirach are two stars in Aries, not more than $5^\{\backslash circ\}$ distant from each other, forming with Mirach an isosceles triangle: the most eastern star, $\backslash alpha$, is of the second magnitude; the other, $\backslash beta$, of the third, attended by a smaller star, marked $\backslash gamma$, of the fourth magnitude. A line drawn from Mirach, perpendicular to the horizon, will pass between the two, and besides, will point to a star of the second magnitude, directly E. not above $3^\{\backslash circ\}$ from the horizon.

"This star is the first of Cetus, marked $\backslash alpha$, and is of the second magnitude: it is named Menkar. A line drawn from Capella through the Pleiades will also point to it. Cetus is a large constellation, and contains eight stars of the third magnitude; they all lie to the west of Menkar; $\backslash beta$, a star in the tail, is more than $40^\{\backslash circ\}$ distant from it. The azimuth of $\backslash beta$ is S. E. by E.; altitude nearly the same as Menkar.

"The constellation Pisces is situated next to Aries; it contains one star of the third magnitude, marked $\backslash alpha$: its altitude is $10^\{\backslash circ\}$, azimuth E. by S. It is distant from Menkar $15^\{\backslash circ\}$. A line drawn from Almaak, through $\backslash alpha$ in Aries, will point to it.

"If we return again to $\backslash alpha$, in the head of Andromeda, we shall find three other stars nearer the meridian, which,

with it, form a square. These stars are in Pegasus, and are placed at the distance of $15^\{\backslash circ\}$ from each other; they are all of the second magnitude. The two stars forming the western side of the square are called—the upper one Scheat, which is marked $\backslash beta$, and which is in the thigh of Pegasus; the under one Markab, which is marked $\backslash alpha$, and which is in the wing; the lower star in the eastern side of the square is in the tip of the wing, and is marked $\backslash gamma$. The altitude of Scheat is $35^\{\backslash circ\}$; azimuth S. E. $\backslash frac\{1\}\{2\}$ E. Altitude of Markab, $43^\{\backslash circ\}$; azimuth S. E. by S. $\backslash frac\{1\}\{2\}$ E.

"A line drawn through $\backslash gamma$ and $\backslash beta$ (the diagonal in the square of Pegasus) and continued to the meridian, will point out Cygnus, a remarkable constellation in the form of a large cross, in which there is a star of the second magnitude, named Deneb, or Arided; it is marked $\backslash alpha$, and is almost directly upon the meridian at the altitude of $80^\{\backslash circ\}$. Cygnus contains six stars of the third magnitude. The constellation Cepheus, which contains no remarkable stars, is situated between Cygnus and the north pole.

"Below Pegasus, and nearer the meridian, is Aquarius, containing four stars of the third magnitude. A line drawn from $\backslash alpha$ in Andromeda, through Markab, will point to $\backslash alpha$ in Aquarius. Its altitude is $32^\{\backslash circ\}$; azimuth S. S. E.

"A bright star of the first magnitude named Fomalhaut, in Pisces Australis, is then upon the horizon; azimuth S. S. E.

"Delphinus is a small constellation, situated about $30^\{\backslash circ\}$ below Cygnus upon the meridian; it contains five stars of the third magnitude, four of them being placed close together, and forming the figure of a rhombus or lozenge. A line drawn through the two under stars of the square will point to it. Its altitude is about $50^\{\backslash circ\}$.

"A little to the west of Delphinus, but not quite so high, is Aquila, containing one very bright star of the first magnitude, named Atair: It may very easily be known from having a star on each side of it of the third magnitude, forming a straight line. The length of the line is only about $5^\{\backslash circ\}$; altitude of Atair $40^\{\backslash circ\}$; azimuth S. S. W.

"Considerably above Atair, and a little to the W. of Cygnus, is Lyra, containing a star of the first magnitude, one of the most brilliant in the firmament. It is called Lyra or Vega, and is $35^\{\backslash circ\}$ to the N. W. of Atair; altitude $60^\{\backslash circ\}$; azimuth W. S. W. Lyra, Atair, and Arid, form a large triangle.

"We come now to notice three constellations, which occupy a large space in the western side of the heavens: these are Hercules immediately below Lyra; Serpentarius between Hercules and the horizon, extending a little more towards the south; and Boötes, reaching from the horizon W. N. W. to the altitude of $45^\{\backslash circ\}$.

"Hercules contains eight stars of the third magnitude; the star in the head, $\backslash alpha$, named Ras Algebi, is within $5^\{\backslash circ\}$ of $\backslash alpha$ in the head of Serpentarius. This last is a star of the second magnitude, and is named Ras Alhague: its altitude is $30^\{\backslash circ\}$; azimuth S. W. by W. $\backslash frac\{1\}\{2\}$ W. A line drawn from Lyra, perpendicular to the horizon, will pass between these two stars. The other stars in Hercules extend towards the zenith, and those in Serpentarius towards the horizon.

"The constellation Boötes may easily be known from the brilliancy of Arcturus, a star of the first magnitude, and supposed to be the nearest to our system of any in the northern hemisphere: it is within $10^\{\backslash circ\}$ of the horizon; azimuth W. N. W. Boötes also contains seven stars of the third magnitude, mostly situated higher in the heavens than Arcturus. The star immediately above Arcturus is called Mezen Mirach, and is marked $\backslash iota$. The star in the left shoulder, $\backslash delta$, named Seginus, forms with Mirach and Arcturus a straight line.

"Between Serpentarius and Boötes is Serpens, containing one star of the second magnitude, and eight of the third: $\backslash alpha$ in Serpens is nearly at the same distance from the horizon, as Arcturus; azimuth W.

"Above Serpens, and a little to the east of Boötes, is the Northern Crown, containing one star of the second magnitude, named Gemma, and several of the third, which have the appearance of a semicircle. A line drawn from Lyra to Arcturus will pass through this constellation.

"We come now to Ursa Major, a constellation containing one star of the first, three of the second, and seven of the third magnitude. It may easily be distinguished by those seven stars, which, from their resemblance to a waggon, are called Charles's Wain. The four stars in the form of a long square, are the four wheels of the waggon; the three stars in the tail of the Bear, are the three horses, which appear fixed to one of the wheels. The two hind wheels, $\backslash alpha$ named Dubhe, and $\backslash beta$, are called the pointers, from their always pointing nearly to the north pole. Hence the pole star may be known. The altitude of Dubhe is $30^\{\backslash circ\}$; azimuth N. by W. $\backslash frac\{1\}\{2\}$ W. The distance between the two pointers is $5^\{\backslash circ\}$; the distance between the pole star and Dubhe, the upper pointer, is $30^\{\backslash circ\}$.

"Ursa Minor, besides the pole star of the second magnitude, situated in the tail, contains three of the third, and three of the fourth magnitude. These form some resemblance to the figure of Charles's Wain inverted, and may easily be traced.

"Draco, containing four stars of the second and seven of the third magnitude, spreads itself in the heavens near Ursa Minor: the four stars in the head are in the form of a rhombus or lozenge: the tail is between the pole star and Charles's Wain.

"Besides these constellations, there are a number of others, which, as they contain no remarkable stars, we have not described; an enumeration of these will suffice. The Lynx, between Ursa Major and Auriga; Camelopardalus, between Ursa Major and Cassiopeia; Musca, and the Greater and Lesser Triangles between Aries and Perseus, Aculeus, close to the head of Pegasus; Sagittarius setting in the south-west; Antinous and Sobieski's Shield below Aquila; the Fox and Goose between Aquila and Cygnus; the Greyhounds and Berenice's Hair between Boötes and Ursa Major, and Leo Minor below Ursa Major *.

The astronomical terms that we must here employ Introduction in describing the method of performing the problems to Geography on the celestial globe, will be found explained in the Sky and Astronomy, 2d article ASTRONOMY, or under their proper heads in the general alphabet of this work. See ASCENSION, AZIMUTH, DECLINATION, &c.

Principles and Practice. PROBLEM II. To find the right ascension and declination of any given star.

Bring the given star below the brazen meridian, and mark the degree of the meridian under which it lies. That degree shews the declination of the star, and the degree of the equator cut by the meridian gives the star's right ascension.

The right ascension of a star may also be found by placing the globe in the position of a right sphere, and then bringing the star to the eastern part of the horizon; for that point of the equator which comes to the horizon at the same time with the star, marks its right ascension. See ASTRONOMY, N^o 249, 250.

Ex. 1. What is the right ascension and declination of the star Sirius? Ans. Its right ascension is 99°, and its declination 16° 27' S.

Ex. 2. Required the right ascension and declination of Aldebaran, or the star in the Bull's Eye marked $\backslash alpha$. Ans. Its right ascension is 66°, and its declination 16° 5' N.

PROBLEM III. Having the right ascension and declination of a star given, to find the star on the globe.

Bring that degree of the equator which marks the right ascension below the brazen meridian, and counting along the meridian towards the north or south, as far as the degree of declination, the required star will be there found.

Ex. 1. The right ascension of a certain star is 162° 15' and its declination is 57° 27' N.; What is the name of the star? Ans. The lower pointer of Ursa major, marked $\backslash beta$.

Ex. 2. The right ascension of Arcturus is 211° 30', and its declination is 20° 13' N.; it is required to find it on the globe.

This problem is extremely useful in discovering the names and relative situations of the different stars.

PROBLEM IV. To find the latitude and longitude of a given star.

Bring the solstitial colure (see N^o 75) below the brazen meridian, and there fix the quadrant of altitude over that pole of the ecliptic which is in the same hemisphere with the given star. Then, keeping the globe steady, bring the graduated edge of the quadrant over the given star, and the degree of the quadrant cut by the star, counted from the ecliptic, marks its latitude, and the degree of the ecliptic that is cut by the quadrant is the longitude of the given star (11). See ASTRONOMY, N^o 252, 253.

Ex. 1. What is the latitude and longitude of Arcturus? Ans. Lat. 31° N. Long. Libra 20°.

Ex. 2. What is the latitude and longitude of Capella? Ans. Lat. 23° N. Long. Gemini 18° 30'.

PROBLEM V. Having the day of the month given, to find at what hour any star comes below the meridian.

Find the sun's place, and bring it to the meridian, and set the horary index to XII.; turn the globe till the given star come below the meridian, and the index will point out the hour.

To know whether the hour is in the forenoon or afternoon, it is necessary to observe, that if the star be to the east of the sun, it will reach the meridian later than the sun, but if it be to the west of the sun, it will come to the meridian sooner: hence, in the former case, the hour will be P. M. and in the latter A. M.

Ex. 1. At what hour does Sirius come to the meridian on the 9th of February? Ans. At 7 minutes past 9 P. M.

Ex. 2. Required the hour when Castor passes the meridian on the same day. Ans. At 52 minutes past 9 P. M.

PROBLEM VI. Having any star given, and a given hour, to find on what day the star will come to the meridian at a given hour.

Bring the given star below the meridian, and set the horary index to the given hour. Make the globe revolve till the index come to twelve at noon; and the day of the month which corresponds to the degree of the ecliptic then below the meridian, found in the calendar circle of the wooden horizon, will be the day required.

Ex. 1. On what day does Algenib, the first star of Perseus, come to the meridian at midnight? Ans. On the 13th of November.

Ex. 2. On what day does Arcturus come to the meridian at 9 o'clock P. M. Ans. On the 10th of June.

PROBLEM VII. Having the latitude, the day of the month and the hour of the night given, to find the altitude and azimuth of any given star.

Rectify the globe for the given latitude; bring the sun's place below the meridian, and set the horary index at XII. then turn the globe till the index point at the given hour. Fix the quadrant of altitude at 90° from the horizon, that is, in the zenith, and bring its graduated edge over the place of the star: the degree of the quadrant intercepted between the horizon and the star is the altitude required; and the distance between the foot of the quadrant and the nearest part of the horizon, will be the azimuth.

It is evident that this problem on the celestial globe is exactly similar to Problem XIII. on the terrestrial globe, for finding the altitude of the sun.

Ex. 1. What will be the altitude and azimuth of Cor Hydræ on the 21st of December at London, at 4 o'clock A. M.? Ans. The altitude 30°, the azimuth S. 14° W.

Ex. 2. Suppose an observer at the Cape of Good Hope, on the 21st of June at midnight; required the altitude and azimuth of Arcturus to him? Ans. Altitude 12°, azimuth N. 55° W.

PROBLEM VIII. Having given the azimuth of any given star, and the day of the month in a given latitude; to find the hour of the night, and altitude of the star.

Rectify the globe as in the last problem; fix the quadrant of altitude in the zenith, and bring it to the given azimuth. Turn the globe till the star comes be-

(11) It must be remembered that the longitude of the heavenly bodies is not estimated in degrees and minutes like their right ascension, but in signs, degrees, and minutes, as the sun's place is reckoned.

Principles and Practice. Low the graduated edge of the quadrant, when the horary index will point out the hour, and the altitude of the star will be seen by the quadrant.

Ex. Suppose the azimuth of Dubhe to be $N.\; 23^\{\backslash circ\}\; W.$ at London on the 1st of September; it is required to find the altitude of the star, and the hour of the night? Ans. The altitude of Dubhe at that time is $31^\{\backslash circ\}$, and the hour is 9 o'clock P. M.

PROBLEM IX. The latitude of the place, the altitude of a star, and the day of the month, being given; to find the azimuth and the hour of the night.

Rectify the globe as before, and having fixed the quadrant of altitude in the zenith, turn the globe and quadrant of altitude till the latter comes over the star at the given degree of altitude. In this position the index will shew the time of night, and the position of the quadrant at the horizon will shew the azimuth of the star.

In the same way the hour of the night and the azimuth of the sun may be found, by fixing a patch on the globe in the sun's place, and bringing it to the quadrant as directed for the star.

As the sun and stars have the same altitude twice in the day, it is proper to know whether they are to be east or west of the meridian; or whether the hour required be in the evening or the morning.

Ex. At Edinburgh, on the 25th of December, in the forenoon, when the sun's altitude is $7^\{\backslash circ\}\; 20\text{'}$, required the hour and the sun's azimuth? Ans. It is 10 o'clock A. M. and the sun's azimuth is $S.\; 27^\{\backslash circ\}\; 30\text{'}\; E.$

PROBLEM X. Having the azimuth of the sun or a star, the latitude of the place, and the hour of the day given; to find the altitude and day of the month.

Rectify the globe for the latitude of the place, fix the quadrant in the zenith, and bring its edge under the given azimuth. Bring the sun's place or the star to the edge of the quadrant, and set the index at the given hour. The degree marked in the quadrant will shew the altitude; and if the globe be turned till the index points to twelve at noon, the day of the month, answering to that degree of the ecliptic which is intersected by the brazen meridian, is the day required.

Ex. The azimuth of the star $\backslash alpha$ in the Northern Crown was observed at London at 9 o'clock P. M. to be $S.\; 89^\{\backslash circ\}\; W.$; required the altitude and day of the month? Ans. Altitude $38^\{\backslash circ\}$; day of the month 1st of September.

PROBLEM XI. Having observed two stars to have the same azimuth; to find the hour of the night.

Rectify the globe as before; turn the globe and move the quadrant till the edge of the latter comes over both stars, and the horary index in this position of the globe will give the hour required.

The following is a simple and easy method of finding when two stars have the same azimuth. Hold a small line with a plummet at its lower extremity between the eye and the two stars, and if both stars fall within the line, they have the same azimuth. The same may be done by observing when any two stars pass behind the perpendicular edge of a wall at the same time.

Ex. Vega and Atair were observed to have the same azimuth at London on the 11th of May; required the hour of the night? Ans. 15 minutes past 2 A. M.

This problem may be applied to the regulating of clocks and watches, by reducing apparent to real time, as explained under ASTRONOMY.

PROBLEM XII. To find the rising, setting, and culminating of any star or planet, its continuance above the horizon, its oblique ascension and descension, and its eastern and western amplitude; the place and day being given.

Rectify the globe as in the foregoing problems; bring the given star or the given planet (finding its place in an ephemeris for the given day, and marking it by a patch on the globe), to the eastern part of the horizon, and the index of the hour circle will point out the time of rising: the degree of the equator that comes to the horizon with the given star or planet, marks its oblique ascension, and the eastern amplitude is shewn by the distance of the star or planet from the eastern part of the horizon.

Bring the star or planet to the meridian, and the index will point to the time of its culminating.

Move the globe till the star or planet come to the western part of the horizon, and the time of its setting, its oblique descension, and its western amplitude, may be found in the same manner as directed above; for its rising, oblique ascension, and eastern amplitude, the number of hours passed over by the index, while the star or planet is moving from east to west, will shew the time of its continuance above the horizon.

Ex. 1. Required the above circumstances with respect to Sirius on the 14th of March at London. Ans. It rises at 24 minutes past two P. M.; comes to the meridian, or culminates, at 57 minutes past six P. M.; and sets at half-past eleven P. M. Hence it remains above the horizon nine hours and six minutes. Its oblique ascension is $120^\{\backslash circ\}\; 47\text{'}$, its oblique descension $77^\{\backslash circ\}\; 17\text{'}$, and its amplitude $27^\{\backslash circ\}\; S.$

Ex. 2. It is required to find the situation of the several planets on the 19th of January 1806. Ans. Mercury is about $22^\{\backslash circ\}$ to the west of the sun, and rises south-east by east, at 20 minutes before seven A. M. Venus is an evening star, and sets about half past eight. Mars is a very little to the east of the sun, and rises and sets so near the same time with the sun, that he cannot be seen. Jupiter is a morning star, and rises about six o'clock. Saturn is a little to the east of the star Spica Virginis, and rises about half an hour after midnight. Herschel is very near Saturn, and rises about the same time.

PROBLEM XIII. To find those stars which never rise, and those which never set, in a given latitude.

Rectify the globe for the latitude of the place; then, holding a black lead pencil so as to touch the surface of the globe at the northern point of the horizon, turn the globe, so that the pencil may describe a circle: all the stars which are between this circle and the elevated pole, never set. Again, holding the pencil at the southern point of the horizon, turn the globe so as to describe another circle there, and all the stars that are between that circle and the pole, below the horizon, never rise.

If the place is in southern latitude, the stars that never set are found by describing a circle at the southern point.

Principles and Practice. point of the horizon, and those that never rise by a similar circle at the northern point (1).

183
Harvest moon illustrated. Throughout almost the whole year, the moon rises later every successive day, by above three quarters of an hour; but at a considerable distance from the equator, as in the latitude of Britain, France, and some other countries, a remarkable anomaly takes place in the moon's motion about the time of harvest. At this season, when the moon is about full, she rises for several nights successively at about 17 minutes only later than on the preceding day. This is attended with considerable advantage, for as the moon rises before twilight is well ended, the light is as it were prolonged, and thus an opportunity given to the industrious farmer to continue longer in the field, for the purpose of gathering in the fruits of the earth. From the advantage derived from the full moon at the season of harvest, it has been called the harvest moon. The following problem has been contrived for the purpose of illustrating the phenomenon by means of the globe.

Rectify the globe for any considerable northern latitude, suppose that of London. As the angle which the moon's orbit makes with the ecliptic is but small, we may suppose, without any considerable error, her orbit to be represented by the ecliptic. In September the sun is in the beginning of $\backslash alpha$, so that the moon, when full, being in opposition to the sun, must be in or near the beginning of $\backslash gamma$. Put a patch, therefore, in the globe at the first point of $\backslash gamma$ in the ecliptic; and as the moon's mean motion is about $13^\backslash circ$ in a day, put another patch on the ecliptic $13^\backslash circ$ beyond the former, and it will point out the moon's place the night after it is full. A third and fourth patch, put at the distance of $13^\backslash circ$ further on, will shew the moon's place on the second and third nights after full, &c. Now, bring the first patch to the horizon, and observe the hour pointed out by the index; turn the globe till the second patch comes to the horizon, and it will appear by the index that there are only 17 minutes between the time of the first patch rising, and that of the second. This small difference in the motion of the moon evidently arises from the small angle which her orbit makes with the horizon. The remaining patches will come to the horizon with a little greater difference of time, and this difference will gradually increase as the moon advances in the ecliptic; but for the first week after the full moon at harvest the difference will not be more than two hours. If patches be continued on to the first point in $\backslash alpha$, it will be found that the time of their rising, or coming to the horizon, will increase considerably till the last will be above $1\backslash frac\{1\}\{2\}$ hour later in coming to the horizon, because that point of the ecliptic makes the greatest angle with the horizon.

The point of the ecliptic, which makes the least angle with the horizon at rising, makes the greatest angle at setting; and, consequently, when the differ-

ence is least at the time of rising, it is greatest at the time of setting.

The difference between apparent time and mean or equal time, has been explained in ASTRONOMY, from $N^\backslash circ\; 50$ to $60$; and the method of computing the equation of time is also there described.

To explain the equation of time on the globe, make, with a black lead pencil, marks all round the equator and ecliptic, beginning with $\backslash gamma$, at equal distances from each other, suppose about $15^\backslash circ$. Then, on turning the globe, it will be seen that all the marks on the first quadrant of the ecliptic, reckoning from $\backslash gamma$ to $\backslash alpha$, come to the brazen meridian sooner than the corresponding marks on the first quadrant of the equator. Now, as the former marks represent time as measured by the sun, or a dial, and the latter represent it as measured by an accurate clock, it will be evident, that through the first quarter the dial is faster than the clock.

Still turning the globe, it will be seen that the marks on the second quarter of the ecliptic, reckoning from $\backslash alpha$ to $\backslash epsilon$, come to the meridian later than the corresponding marks of the equator; consequently in this quarter the sun or the dial is slower than the clock. By moving the globe round, and marking the approach of the dots in the third quadrant, it will be seen that, as in the first, the dial now precedes the clock, and in the fourth quadrant, that it is behind it, according to the explanation given in ASTRONOMY.

The construction of globes is of considerable importance; as, in performing the problems in which they are constructed, very much depends on the accuracy with which they have been constructed. We shall here, therefore, describe pretty minutely the methods in which the artills of Britain and France make their globes.

There are certain general circumstances which are attended to in the construction of every globe.

There is first provided a wooden axis, somewhat less than the intended diameter of the globe, and to the extremities of this axis, which is the basis of the whole succeeding structure, there are fixed two metallic wires, to serve as poles. Now, two hemispherical caps formed on a wooden mould or clock, are applied in the axis. These caps are composed of pasteboard, or folds of paper laid one over another on the mould, till they are of the thickness of a crown piece; and after the whole has stood to dry, and has become a solid body, an incision is made with a sharp knife along the middle, and the two caps are thus slipped off the mould. These caps are now to be applied on the poles of the axis, as they were before on those of the mould; and to fix them

(1) This problem may be performed without the globe, by the following method. Find the latitude of the place in a table, and subtract it from $90^\backslash circ$; the remainder will be the complement of the latitude. Then, if the declination of the given star be of the same name with the co-latitude, and exceed it in quantity, it will never set. If it be of a contrary name, and exceed it, it will never rise.

them firmly on the axis, the two edges are sewed together with packthread.

When the rudiments of the globe are thus laid, the artist proceeds to strengthen the work, and make the surface smooth and equal. For this purpose, the two poles are fixed in a metallic femicircle, of the proposed size; and a composition made of whitening, mixed with water and glue, heated, melted, and incorporated together, is daubed all over the paper surface. While the plaster is applied, the globe is turned round in the femicircle, the edge of which pares away all the matter that is superfluous and exceeds the proper dimensions, and spreads the rest over those parts that require it. After this operation the ball stands to dry, and when it is thoroughly dried, it is again put in the femicircle, and fresh plaster applied to it; and thus they continue to apply composition and dry the ball alternately, till the surface accurately touches the femicircle in every point, when it becomes perfectly firm, smooth, and equal.

When the ball of the globe is thus finished, the map, containing a delineation of the surface of the earth, is to be pasted on the globe. For this purpose, the map is engraved in several gores or gullets, so that when these are accurately joined together on the spherical surface, they may cover every part of the ball, without overlapping each other. The greatest nicety is required in forming these engraved gullets, as well in the accuracy of the engraving, as in the choice and shape of the paper employed. The method of describing the gores or gullets, usually employed by the British artists, is as follows.

1. From the given diameter of the globe there is found a right line AB (fig. 12.), equal to the circumference of a great circle corresponding to that diameter; and this line is divided into 12 equal parts.

2. Through the several points of division, 1, 2, 3, 4, &c. with a distance equal to ten of the divisions, arches are described crossing each other as in D and E; and these figures are pasted on the globe, so as when joined together to cover its whole surface.

3. Each part of the line AB is divided into 30 equal parts, so that the whole line, which may represent the equator, is divided into $360^\backslash circ$.

4. From the points D and E, which represent the poles, with a distance $=\; 23\backslash frac\{1\}\{2\}^\backslash circ$, there are described arches $ab,\; a\text{'}b\text{'}$, (fig. 13.) which form twelfth parts of the polar circles.

5. In a similar manner about the same poles D and E, with a distance $=\; 66\backslash frac\{1\}\{2\}^\backslash circ$, reckoned from the equator, there are described other arches, $cd,\; c\text{'}d\text{'}$, which are the twelfth parts of the tropics.

6. In forming the celestial globe, through the point of the equator marked $e$ (fig. 13.) representing the right ascension of a given star, and through the two poles D and E, there is drawn an arch of a circle; and if the complement of the declination from the pole D be taken in the compasses, and an arch be described, intersecting the former in the point $i$, this point $i$ will be the place of the given star.

7. In this way all the stars of each constellation are laid down, and the circumscribing outline of the constellation is drawn as figured in the tables of Bayer, Flamsteed, &c.

8. In the same manner are determined the declinations and right ascensions of every degree of the ecliptic, $d,\; g$.

The above is the method described by Mr Chambers,

of laying down or delineating the gores of a celestial globe. Those of the terrestrial globe are delineated in much the same manner, only that every place is laid down on the gores, according to its longitude and latitude, determined by the intersection of circles; and then the outline of the coasts, boundaries of countries, &c. are added, like the figures of the constellations above mentioned.

9. When the surface of the globe has been thus projected on a plane, the gullets are to be engraved on copper, to save the trouble of making a new projection for every globe.

10. In the mean time, a ball of paper, plaster, or the like, of the intended diameter of the globe, is prepared in the manner above described, and by means of a femicircle and style, great circles are drawn on its surface, so as to divide it into a number of equal parts, corresponding to the number of gullets; and subdividing each of these according to the other lines and divisions of the globe. When the ball is thus prepared, the gullets are to be accurately cut from the printed engraving, and pasted on the ball.

When the papers have been thus pasted on, and suffered to dry, nothing remains but to colour and illuminate the globe, and to cover it with a thin layer of the finest varnish, that it may the better resist dust and moisture. The ball of the globe is now finished, and is to be hung in a strong brazen meridian, furnished with hour circles and a quadrant of altitude, and fitted into a strong wooden horizon.

The method employed by the French artists in projecting the gullets of globes, is thus described by M. forming the gullets. La Lande.

"To form celestial and terrestrial globes, it is necessary to engrave gores, which are a sort of projection or development of the globe. The length PC (fig. 14.) of the axis of the curve, is equal to a fourth part of the circumference of the intended globe; the intervals of the parallels on the axis PC are all equal; the radii of the circles K D I, which represent the parallels, are equal to the co-tangents of the latitudes, and the arches of each, such as KI, are nearly equal to the number of degrees that correspond to the breadth of the gore (usually $30^\backslash circ$), multiplied by the sine of the latitude: thus, there will be found no difficulty in tracing them; but the principal difficulty proceeds from the change which those parts of the gores undergo, when they are glued upon the globe; as, in order to adjust them to the space which they ought to occupy, it is necessary to make the paper less on the sides than in the middle, because the sides are too long.

"The method employed by artists for engraving these gores, is thus described by Bion (Usage des Globes, tom. iii.), and by Robert de Vaugondy in the seventh volume of the Encyclopédie, and this method is sufficient for practical purposes.

"Draw on the paper a line AC, equal to the chord of $15^\backslash circ$, to make the half breadth of the gore; and a perpendicular PC, equal to three times the chord of $30^\backslash circ$, to make the half length: for these papers, the dimensions of which will be equal to the chords, become equal to the arcs themselves when they are pasted on the globe. Divide the height CP into nine parts, if the parallels are to be drawn in every $10^\backslash circ$; divide also the quadrant BE into nine equal parts; through each division

Principles and Practice. vision point of the quadrant, as G, and through the corresponding point D of the right line CP, draw the perpendiculars HGF and DK, the meeting of which in F gives one of the points of the curve BFP, which will terminate the circumference of the gore. When a sufficient number of points are thus found, trace the outline PIB with a curved rule. By this construction are given the gore breadths, which are on the globe, in the ratio of the cosines of the latitudes, supposing those breadths taken perpendicular to CD, which is not very exact; but it is impossible to prescribe a rigid operation sufficient to make a plane which shall cover a curved surface, and that on a right line AB shall make lines PA, PC, PD, equal to each other, as they ought to be on the globe. To describe the circle KDI, which is at the distance of $30^\backslash circ$ from the equator, there must be taken above D, a point that shall be distant from D the value of the tangent of $60^\backslash circ$, which may be taken either from tables, or may be measured on a circle equal to the circumference of the globe that is to be drawn; this point will serve as a centre for the parallel DI, which ought to pass through the point D; for it is supposed equal to that of a cone circumscribing the globe, and which would touch it at the point D.

"The meridians are traced to every $10^\backslash circ$, by dividing each parallel, as KI, into three equal parts at the points L and M, and drawing from the pole P, through all these points of division, curves which represent the intermediate meridians lying between PA and PB, such as BR and ST (fig. 15.)

"The ecliptic AQ (fig. 15.) is traced by means of the known declination, from different points of the equator, as found in the tables; for $10^\backslash circ$ it is equal to $3^\backslash circ\; 58\text{'}$; for $20^\backslash circ\; =\; 7^\backslash circ\; 50\text{'}\; =\; BQ$ $20\text{'}$; for $30^\backslash circ\; =\; 11^\backslash circ\; 29\text{'}$, &c."

In general, it is observed that the paper on which maps are printed, such as that called in France colombier, contracts itself $\backslash frac\{1\}\{4\}$, or a line in six inches, upon an average, when it is dried after printing; hence it is necessary to prevent this inconvenience in engraving the gores: if, however, notwithstanding this, the gores are still found too short, it must be remedied by taking from the surface of the ball a little of the white with which it is covered; thus making the dimensions of the ball correspond to those of the gores as they are printed. But, what is singular, in drawing the gore, moistened with the paste to apply it on the globe, the axis GH lengthens, and the side AN shortens in such a manner that neither the length of the side ACK, nor that of the axis GEH of the gore are exactly equal to the quarter of the circumference of the quarter of the globe, when compared to the figure on the copper, or to the numbers shown on the side of fig. 15.

"Mr Bonne having made several experiments on the dimensions which the gores take after being covered with paste in order to apply them to the globe, especially of the paper called jesus, which had been employed in covering globes of a foot in diameter; found that it was necessary to give to the gore engraved on copper the dimensions laid down in fig. 15. Supposing that the radius of the globe contains 720 parts, the half of the breadth of the gore $AG\; =\; 188.5$; the distance AC for the parallel of $10^\backslash circ$ taken on the straight line LM is $=\; 128.1$, the small deviation from the parallel of $10^\backslash circ$ in the middle of the gore ED is 4, the

line ABN is a straight line, the radius of the parallel of $10^\backslash circ$ or of the circle OET, is 4083, &c. The small circular cap which is placed under H, has its radius 253, instead of 247, which it would have if the line of $20^\backslash circ$ had been the radius of it."

Globes are made of various sizes, from a diameter of three inches, to that of as many feet; but their most usual diameter is that of 18 inches, which are sufficiently large for most of the purposes for which globes are employed. Some large globes were made about 100 years ago, in France, by P. Coronelli, a Franciscan monk, which were in considerable reputation. They were engraved, and the plates are still to be seen at Paris, at the house of M. Desnos, in the Rue St Jacques. There are some large globes at Cambridge, which were drawn by the hand; but the largest globes of which we have any account, are those which were made for the late unfortunate Louis XVI. and were kept in the palace of Marly. They were 12 feet in diameter, and we believe, are still existing at Paris, where they occupy four entire rooms, each of them being partly in an upper room, and partly in that below it, the floor of the upper room forming the horizon.

The account which we have given of the method of constructing globes, will be useful to those who purchase these instruments; but to assist them still further, we shall subjoin the following practical rules for the choice of globes.

1. The papers should be well and neatly pasted on the globes, which may be known by the lines and circles meeting exactly, and continuing all the way even and whole; the circles not breaking into several arches, nor the papers either coming short, or lapping over one another.

2. The colours should be transparent, and not laid too thick upon the globe, to hide the names of the places.

3. The globe should hang evenly between the brazen meridian and the wooden horizon, not inclining either to the one side or the other.

4. The globe should move as close to the horizon and the meridian as it conveniently may, otherwise there will be too much trouble to find against what part of the globe any degree of the meridian or horizon is.

5. The equinoctial line should be even with the horizon all round, when the north or south pole is elevated $90^\backslash circ$ above the horizon.

6. The equinoctial line should cut the horizon in the east and west points, in all the elevations of the pole from 0 to $90^\backslash circ$.

7. The degree of the brazen meridian marked 0, should be exactly over the equinoctial line of the globe.

8. Exactly half of the brazen meridian should be above the horizon, which may be known by bringing any of the decimal divisions on the meridian to the north point of the horizon, and finding their complement to $90^\backslash circ$ on the south point.

9. When the quadrant of altitude is placed as far from the equator, or the brazen meridian, as the pole is elevated above the horizon, the beginning of the degrees of the quadrant should reach just to the plane surface of the horizon.

10. When the index of the hour circle passes from one.

one hour to another, 15 degrees of the equator must pass under the graduated edge of the brazen meridian.

11. The wooden horizon should be made substantial and strong; it being generally observed, that, in most globes, the horizon is the first part that fails, on account of its having been made too slight.

103 In using a globe, the eastern side of the horizon should be kept towards the observer, (unless in particular problems which require a different position); and that side may be known by the word east on the horizon. In this position the observer will have the graduated side of the meridian towards him, and the quadrant of altitude directly before him; and the globe will be exactly divided into two equal parts by the graduated side of the meridian.

In performing some problems, it will be necessary to turn about the whole globe and horizon, in order to look at the west side; but this turning will be apt to disturb the ball, so as to shift away that degree of the globe which was before set to the horizon or meridian. This inconvenience may be avoided by thrusting the feather end of a quill between the ball of the globe and the brazen meridian, and thus, without injuring the surface of the globe, it will be kept from turning in the meridian, while the whole is moved round, so as to examine the western side.

We have already mentioned some improvements which have been made on the globes, for the purpose of remedying the defect in the old construction, of placing the hour circles on the outside of the brazen meridian. Some other improvements and modifications have been contrived by various artists; but of these we shall only mention those of Mr Senex, Mr B. Martin, Mr Smeaton, and Mr Adams.

Mr John Senex, F.R.S. invented a contrivance for remedying these defects, by fixing the poles of the diurnal motion to two shoulders or arms of brass, at the distance of $23\backslash frac\{1\}\{2\}^\backslash circ$ from the poles of the ecliptic. These shoulders are strongly fastened at the other end to an iron axis, which passes through the poles of the ecliptic, and is made to move round with a very stiff motion; so that when it is adjusted to any point of the ecliptic which the equator is made to intersect, the diurnal motion of the globe on its axis will not disturb it. When it is to be adjusted for any particular time, either past or future, one of the brazen shoulders is brought under the meridian, and held fast to it with one hand, while the globe is turned about with the other; so that the point of the ecliptic which the equator is to intersect may pass under the 0 degree of the brazen meridian; then holding a pencil to that point, and turning the globe about, it will describe the equator according to its position at the time required; and transferring the pencil to $23\backslash frac\{1\}\{2\}^\backslash circ$ and $66\backslash frac\{1\}\{2\}^\backslash circ$ degrees on the brazen meridian, the tropics and polar circles will be so described for the same time. By this contrivance, the celestial globe may be so adjusted, as to exhibit not only the rising and setting of the stars in all ages and in all latitudes, but likewise the other phenomena that depend upon the motion of the diurnal round the annual axis. Senex's celestial globes, especially the two greatest, of 27 and 28 inches in diameter, have been constructed upon this principle; so that by means of a nut and screw, the pole of

the equator is made to revolve about the pole of the ecliptic.

To represent the above appearances in the most natural and easy manner, Mr B. Martin applied to the contrivance of Mr Senex a moveable equinoctial and solstitial colure, a moveable equinoctial circle, and a moveable ecliptic; all so connected together as to represent those imaginary circles in the heavens for any age of the world.

110 In order to the performance of the problems which improve- relate to the altitudes and azimuths of celestial objects, Mr Smeaton, F.R.S. has made some improvements applicable to the celestial globe; and to give some idea of the construction, they may be described as follows: Instead of a thin flexible slip of brass, which generally accompanies the quadrant of altitude, Mr Smeaton substitutes an arch or a circle of the same radius, breadth, and substance, as the brass meridian, divided into degrees, &c. similar to the divisions of that circle, and which, on account of its strength, is not liable to be bent out of the plane of a vertical circle, as is usual with the common quadrant put to globes. That end of this circular arch at which the division begins, rests on the horizon, being filed off square to fit and rest steadily on it throughout its whole breadth; and the upper end of the arch is firmly attached, by means of an arm, to a vertical socket, in such a manner that when the lower end of the arch rests on the horizon, the lower end of this socket shall rest on the upper end of the brass meridian, directly over the zenith of the globe. This socket is fitted to and ground with a steel spindle of the length, so that it will turn freely on it without shaking; and the steel spindle has an apparatus attached to its lower end, by which it can be fastened in a vertical position to the brass meridian, with its centre directly over the zenith point of the globe. The spindle being fixed firmly in this position, and the socket which is attached to the circular arch put on it, and so adjusted that the lower end of the arch just rests on and fits close to the horizon; it is evident that the altitude of any object above the horizon will be shewn by the degree which it intersects on this arch, and its azimuth by that end of the arch which rests on the horizon.

Besides this improvement, Mr Smeaton proposes that, instead of fixing the hour index, as is usually done, on one end of the axis, it be placed in such a manner that its upper surface may move in the plane of the hour circle rather than above it. To effect this, he directs the extremity of the index to be filed off so as to form a circular arc, of the same radius with the inner edge of the hour circle, to which it is made to fit exactly, and a fine line is drawn in the middle of its upper surface, to point out the hour, instead of the tapering point usually employed. By this contrivance, if the hour circle be made four inches in diameter, the time may be shewn to half a minute. For a more particular account of Mr Smeaton's improvements, we refer the reader to the 79th volume of the Philosophical Transactions.

Another improvement of the celestial globe, by which it is better adapted to astronomical purposes, is described in the article ASTRONOMY, Vol. III. p. 178.

Besides the modifications in the construction of globes, introduced by Mr Adams, and which have been al-

Principles and Practice. ready described, there are some others which we must briefly mention, respecting principally the placing the globe in an inclined position, and fitting it with a moveable or floating meridian and horizon.

The globes constructed after this manner do not hang in a frame like the ordinary globes, but are fixed on a pedestal, and supported by an axis which is inclined $66\backslash frac\{1\}\{2\}^\{\backslash circ\}$ to the ecliptic, and is of course always parallel to the axis of the earth, supposing the orbit of this planet to be parallel to the ecliptic. On the pedestal below the globe is a graduated circle, marked with the signs and degrees of the ecliptic; and adjoining to this is a circle of months and days, answering to every degree of the ecliptic; and within this is a third circle shewing the sun's declination for every day of the month. There is a moveable arm on the pedestal, which being set to the day of the month, immediately points out the sun's place and declination.

Round the globe there is a circle representing the horizon of any place, and at right angles to this is fixed a semicircle, serving for a general meridian. The middle point of this semicircle serves to represent the situation of any inhabitant on the earth; for this purpose there is fixed a steel pin over the middle point of this semicircle.

Mr Adams alleges that only one supposition is necessary for performing every problem with this globe, namely, that a spherical luminous body will enlighten one half of a spherical opaque body, and consequently that a circle at right angles with the central solar ray, and dividing the globe in half, will be a terminator shewing the boundary of light and darkness for any given day. For this purpose, at the end of the moveable arm, opposite to the sun, there is a pillar, from the top of which projects a piece carrying a circle that surrounds the globe, dividing it into equal portions, and separating the illuminated from the dark parts; and $18^\{\backslash circ\}$ behind this there is another circle parallel to it, representing the limit of twilight.

There are two plates below the globe, which are turned by the diurnal revolution of the globe, each of them being divided into twice 12 hours, and on the outside being marked with the degrees of longitude corresponding to every hour; so that these circles give at sight the hour of the day at any two places on the globe, and the corresponding difference of longitude.

The celestial globe is mounted in a similar manner, except that it is fixed on the axis, and the ecliptic exactly coincides with the sun's apparent path from the earth*.

SECT. IV. Of the Armillary Sphere.

If a machine be constructed that is composed only of the circles of the sphere, and made so as to revolve like a globe, a great many of the most useful problems relating to the heavenly bodies may be solved by it. An instrument of this kind is called an armillary sphere, and of these there are various forms. One of the most convenient is that contrived by the late Mr James Ferguson, and is thus described in his Lectures. It is represented at fig. 16.

The exterior parts of this machine are a compages of brass rings, which represent the principal circles of

the heaven, viz. 1. The equinoctial AA, which is divided into 360 degrees, (beginning at its intersection with the ecliptic in Aries) for shewing the sun's right ascension in degrees; and also into 24 hours, for shewing his right ascension in time. 2. The ecliptic BB, which is divided into 12 signs, and each sign into 30 degrees, and also into the months and days of the year, in such a manner, that the degrees or points of the ecliptic in which the sun is on any given day, stands over that day in the circle of months. 3. The tropic of Cancer, CC, touching the ecliptic at the beginning of Cancer in $\backslash epsilon$; and the tropic of Capricorn DD, touching the ecliptic at the beginning of Capricorn in $\backslash zeta$; each $23\backslash frac\{1\}\{2\}$ degrees from the equinoctial circle. 4. The Arctic circle E, and the Antarctic circle F, each $23\backslash frac\{1\}\{2\}$ degrees from its respective pole at N and S. 5. The equinoctial colure GG, passing through the south and north poles of the heaven at N and S, and through the equinoctial points Aries and Libra, in the ecliptic. 6. The solstitial colure HH, passing through the poles of the heaven, and through the solstitial points Cancer and Capricorn, in the ecliptic. Each quarter of the former of these colures is divided into 90 degrees, from the equinoctial to the poles of the world, for shewing the declination of the sun, moon, and stars; and each quarter of the latter, from the ecliptic at $\backslash epsilon$ and $\backslash zeta$, to its poles $b$ and $d$, for shewing the latitudes of the stars.

In the north pole of the ecliptic is a nut $b$, to which is fixed one end of a quadrantal wire, and to the other end a small sun Y, which is carried round the ecliptic BB, by turning the nut; and in the south pole of the ecliptic is a pin at $d$, on which is another quadrantal wire, with a small moon Z upon it, which may be moved round by hand; but there is a particular contrivance for causing the moon to move in an orbit which crosses the ecliptic at an angle of $5\backslash frac\{1\}\{2\}$ degrees, in two opposite points called the moon's nodes; and also for shifting these points backward in the ecliptic, as the moon's nodes shift in the heaven.

Within these circular rings is a small terrestrial globe I, fixed on the axis KK, which extends from the north and south poles of the globe at $n$ and $s$, to those of the celestial sphere at N and S. On this axis is fixed the flat celestial meridian LL, which may be set directly over the meridian of any place on the globe, and then turned round with the globe, so as to keep over the same meridian upon it. This flat meridian is graduated the same way as the brass meridian of a common globe, and its use is much the same. To this globe is fitted the moveable horizon MM, so as to turn upon two strong wires proceeding from its east and west points to the globe, and entering the globe at opposite points of its equator, which is a moveable brass ring let into the globe in a groove all around its equator. The globe may be turned by hand within this ring, so as to place any given meridian upon it, directly under the celestial meridian LL. The horizon is divided into 360 degrees all around its outermost edge, within which are the points of the compass, for shewing the amplitude of the sun and moon, both in degrees and points. The celestial meridian LL, passes through two notches in the north and south points of the horizon, as in a common globe; but here, if the globe be turned round, the horizon and the meridian turn with it. At the south pole

* Adams's
Lectures,
vol. iv.
p. 199.

II.
Armillary
sphere.

of the sphere is a circle of 24 hours, fixed to the rings, and on the axis is an index which goes round that circle, if the globe be turned round its axis.

The whole fabric is supported on a pedestal N, and may be elevated or depressed upon the joint O, to any number of degrees from 0 to 90, by means of the arc P, which is fixed into the strong brass arm Q, and slides in the upright piece R, in which is a screw at r, to fix it at any proper elevation.

In the box T are two wheels and two pinions, whose axes come out at V and U; either of which may be turned by the small winch W. When the winch is put upon the axis V, and turned backward, the terrestrial globe, with its horizon and celestial meridian, keep at rest; and the whole sphere of circles turns round from east, by south, to west, carrying the sun Y, and moon Z, round the same way, causing them to rise above and set below the horizon. But when the winch is put upon the axis U, and turned forward, the sphere with the sun and moon keep at rest; and the earth, with its horizon and meridian, turn round from west, by south, to east; and bring the same points of the horizon to the sun and moon, to which these bodies come when the earth kept at rest, and they were carried round it; shewing that they rise and set in the same points of the horizon, and at the same times in the hour circle, whether the motion be in the earth or in the heaven. If the earthly globe be turned, the hour index goes round its hour circle; but if the sphere be turned, the hour circle goes round below the index.

And so, by this construction, the machine is equally fitted to shew either the real motion of the earth, or the apparent motion of the heaven.

To rectify the sphere for use, first slacken the screw r in the upright stem R, and taking hold of the arm Q, move it up or down until the given degree of latitude for any place be at the side of the stem R; and then the axis of the sphere will be properly elevated, so as to stand parallel to the axis of the world, if the machine be set north and south by a small compass; this done, count the latitude from the north pole upon the celestial meridian LL, down-towards the north notch of the horizon, and set the horizon to that latitude; then turn the nut b until the sun Y comes to the given day of the year in the ecliptic, and the sun will be at its proper place for that day: find the place of the moon's ascending node, and also the place of the moon, by an Ephemeris, and set them right accordingly: lastly, turn the winch W, until either the sun comes to the meridian LL, or until the meridian comes to the sun (according as you want the sphere or the earth to move), and set the hour index to the XII. marked noon, and the whole machine will be rectified. Then turn the winch, and observe when the sun or moon rise and set in the horizon, and the hour index will shew the times thereof for the given day.

Those who have made themselves acquainted with the use of the globes, as described in the first and second sections of this chapter, will be at no loss to perform many problems respecting the motions of the heavenly bodies by means of this sphere.

Dr Long, some years ago, constructed an armillary sphere of glass, in Pembroke hall at Cambridge. It was 18 feet in diameter, and could contain below it more than 30 persons, sitting in such a manner with-

in the sphere, as to view from its centre the representation of the heavens drawn in its concavity. The lower part of the sphere, or that part which is not visible in the latitude of Britain, is wanting; and the whole apparatus is so contrived, that it may be turned round with as little exertion as is requisite to wind up a common jack. Dr Long has given a description of this sphere, accompanied with a figure, in his Astronomy.

The invention of the armillary sphere is thought by La Lande to be as ancient as that of astronomy itself. It has been attributed to Atlas, to Hercules, to Anaximander, and Muses; while others have supposed that it originated in Egypt. The sphere of Archimedes, which became so celebrated, appears to have been something like that of Dr Long, as it was certainly composed of a globe of glass, which, besides containing the circles of the sphere, served as a planetarium, and represented the motions of the planets. Claudian has celebrated it in some beautiful lines. See ARCHIMEDES.

A combination of the armillary sphere with a planetarium was constructed by the late Mr George Adams, and is figured in Plate XIII. fig. 1. of his Astronomical and Geographical Essays.

CHAP. III. Of the Construction and Use of Maps and Charts.

SECT. I. Description of Maps and Charts.

It has been seen, that the surface of the earth may be delineated, in the most accurate manner, on the surface of a globe or sphere. This mode of delineation, however, can be employed only for the purpose of representing the general form and relative proportions of countries on a very confined scale; and is, besides, from its bulk and figure, not well suited to many of the purposes of the geographer. To obviate these inconveniences, recourse has been had to maps and charts, or delineations of the earth's surface on a plane; where the form and boundaries of the several countries, and the objects most remarkable in each, whether by sea or land, are represented according to the rules of perspective, so as to preserve the remembrance that they are parts of a spherical surface. In this way, the several countries or districts of the earth may be represented on a larger scale, and delineations of this kind admit of more easy reference.

In maps, the circles of the sphere, and the boundaries of the countries within them, are drawn as they would appear to an eye situated in some point of the sphere, or at a considerable distance above it. In maps of any considerable extent of country, the meridians and parallels of latitude are circular lines, but, if the map represents only a small district, as a province or county, those circles become so large, that they may, without any considerable error, be represented by straight lines. In charts, which are also called hydrographical maps, as they are representations rather of the water than land, the meridians and parallels are usually represented by straight lines, crossing each other at right angles, as in the smaller maps; and, in particular parts, there are drawn lines diverging from several points, in the direction of the points of the compass, in order to mark the

the bearings of particular places. In maps, the inland face of the country is chiefly regarded in the delineation; but in charts, which are designed for the purposes of navigation, the internal face of the land is left nearly blank, and only the sea-coast, with the principal objects on it, such as churches, light-houses, beacons, &c. are accurately delineated; while particular care is taken to mark the rocks, shoals, and quicksands in the sea, that may endanger the safety of vessels; the depths or soundings of the principal bays and harbours, and the direction of the winds, where these are stationary or peculiarly prevalent. Another distinction of maps and charts is, that in the former, the sea-coast is shaded on the side next the land, while, in the latter, it is shaded towards the sea.

In maps the upper side represents the north, the lower side the south; that on the right hand the east, and that on the left hand the west. All the margins of the map are graduated; the upper and lower margins the degrees of longitude, and the right and left margins the degrees of latitude. (See fig. 1. to which the reader must refer in going over the following description). If the map is on a small scale, only every ten degrees of longitude or latitude are marked on the margin; but, if the map is drawn on a large scale, every degree is numbered, and sometimes every half degree is marked with the number 30 in smaller figures. The space included between every ten degrees in small maps, or between every two degrees in those on a larger scale, is usually divided into ten spaces, which are alternately left blank, and marked with parallel lines, to denote the subdivisions of single degrees or minutes. Through every ten degrees of latitude a line is drawn, representing a parallel of latitude; and through every ten degrees of longitude, or at smaller intervals in each, where the size of the map will admit of it, there are drawn lines representing meridians. In some maps these lines are continued from side to side, or from top to bottom, across both sea and land; but in other maps, they are sometimes only drawn across the sea. The first meridian, however, and the principal circles of the sphere, as the equator, tropics, &c. should always be drawn directly across the map. In most maps, it is marked on the margins, whether the longitude is east or west, and the latitude north or south; but, if this is not marked, it may easily be known, by observing towards what part of the map the degrees increase. If the degrees of latitude increase from the lower to the upper part of the map, the country delineated lies in north latitude; but if they increase from above downwards, it lies in south latitude. Again, if the degrees of longitude increase towards the right, the countries are in east longitude; but if towards the left, they are in west longitude.

The principal objects that diversify the face of the country delineated in the map, such as rivers, mountains, forests, lakes, roads, cities, towns, forts, &c. are marked in such a manner, as that they may be most easily distinguished. A river is denoted by a black crooked line, drawn very fine towards the source or head of the river, and gradually becoming broader as it approaches towards the mouth; and the lesser rivers, or rivulets, which unite their waters with those of the principal stream, are denoted by similar lines appearing to branch off from the first.

Mountains are represented by the figures of little hills;

and if these figures are placed in a row, they denote a ridge of mountains running across the land. If a mountain is a volcano, it is denoted in the map by the appearance of smoke issuing from its summit. Woods or forests are represented by a number of little trees or shrubs, placed in a group. Lakes are denoted by a circumscribed spot shaded with dark lines, and bays or fens by a more regular spot of the same kind, more lightly shaded, or, where the map is coloured, painted of a light green. Roads are represented in a map by two straight lines drawn parallel to each other, for the principal roads, or by a single straight line for the lesser or cross roads. Cities are denoted by a large house, or the figure of a church with the steeple in the middle; and if the city is the metropolis of the country, this is denoted by a white circular space in the middle of the house or church. Small towns are usually represented by circles; and where a small church with the steeple at one end occurs, it denotes a parish. Where the map is on a large scale, or represents only a small district, the towns are denoted by a group of small houses, or more commonly by a number of small shaded spots on each side of the road. A fort, castle, or fortified town, is denoted by a semicircular space surrounded by an angular edge representing bastions. The shoals upon the coast are represented by small dots; the depth of water in bays and harbours by figures, denoting the number of fathoms, among which is sometimes drawn the figure of an anchor, to shew that in that place there is good anchorage for ships.

The boundaries or limits that divide countries from each other are distinguished in maps by dotted lines drawn round each country or district, in such a direction as to show its proper form. Where the map is coloured, the countries or districts are distinguished from each other by the side of the boundary next each being shaded by a different colour from that of the adjoining. Thus, in a map of Europe, the boundary of France may be shaded green, that of Spain red, that of Italy yellow, that of Germany blue, &c. In one corner of the map there is usually drawn a scale divided into a number of equal parts, by which the number of miles or leagues from one part of the map to another may be measured. Sometimes the parts into which the scale is divided are used to denote geographical miles, of 60 to a degree; but more commonly they correspond to the miles in use in the country where the map is made, as, in Britain, to British statute miles of 69 $\backslash frac\{1\}\{2\}$ to a degree.

To mark more distinctly the bearings of different parts of the map, there is usually added in some blank space a circle with four radii, marking the four cardinal points of the compass; the north point being distinguished by the figure of a fleur de lis, and the east point by a cross.

Till of late, the only distinction between the land and water in maps and charts, was afforded by the shading of the sea coast, as mentioned above. In this way, however, the eye cannot easily and expeditiously distinguish the form and extent of the land; and, where the shading is carried much beyond the boundary of the coast, as is often done, especially in engraving small islands, the land is made to appear much larger than it really is.

The ingenious Mr Wilson Lowry having lately contrived an instrument for engraving parallel straight lines, in a much more clear and commodious way than

than could be done by the common graver, it occurred to Mr Pinkerton, while preparing his Modern Geography, that this invention might be applied with advantage to the improvement of maps. A set of maps was, accordingly engraved by Mr Lowry for Pinkerton's Geography, in which the water was marked by dark parallel lines to discriminate it from the land. These lines are drawn horizontally; and Mr Pinkerton proposed that, in engraving charts, the land should be marked with similar lines drawn in a perpendicular direction, while the water should be left blank. This improvement has since been adopted by other constructors of maps and charts, and bids fair to be generally used. The effect is pleasing; and the progress of instruction will be greatly facilitated by the new method, as the extent and bearings of the several countries are seen, as it were, with a glance of the eye. In many of these maps which we have seen, however, the lines are drawn too strongly, which renders the sea so dark, that the names of islands and places on the sea coast can with difficulty be perused. As the line of coast in these maps is strongly marked, the parallel lines denoting the sea should be engraved in a light and soft style; and in this way Mr Lowry's first specimens are executed.

SECT. II. Of the Construction of Maps and Charts.

THE construction of maps consists in making a projection of the surface of the globe on the plane of some one of its circles, supposing the eye to be placed in some particular point. The describing of these projections depends on the principles of perspective, and the projection of the sphere. The general principles will be explained under those articles, but the particular mode of drawing maps properly forms a part of the present treatise.

The methods of constructing maps vary according to the size or scale of the map, and to the projection employed in constructing it.

There are three projections employed in constructing maps, the orthographic, the stereographic, and the globular. In the orthographic projection the eye is supposed to view the part of the globe to be projected, from an infinite distance. In this projection the parts about the middle of the map are very well represented, but those towards the margin are too much contracted.

In the stereographic projection, the eye is supposed to be situated in the surface of the globe to be represented, and looking towards the opposite surface. This is the method usually employed in constructing most maps, especially maps of the world, or planispheres.

In constructing a map of the world, as well as most partial maps, the part of the sphere to be represented is supposed to be in the position of a right sphere (see No. 90). In this mode of projection, the hemisphere to be represented is supposed to be delineated on the plane of that meridian by which it is bounded, in the same manner as its concave surface, conceiving the sphere to be transparent, would appear to an eye placed in the opposite hemisphere, where the equator crosses a meridian; that is, 90° distant from that which forms the plane of the projection. In a delineation of this kind, the meridians and parallels of latitude are represented by arches of circles, except the equator and the central meridian, which are straight lines; and each paral-

lel or meridian forms an arc of a greater circle, in proportion as it approaches nearer to the centre of the map.

By either of these projections only half the globe can be represented in one projection; but in the map of the world, the two hemispheres are usually drawn on the plane of the same circle, adjacent to each other. By Mercator's projection, usually employed for charts, and to be described presently, the whole globe may be represented in one projection, but much distorted.

If the projection of a map of the world be formed on the plane of a meridian, the two projections will represent the eastern and western hemispheres of the globe.

When the projection is made on the plane of the equator, in the situation of a parallel sphere, the projections represent the northern and southern hemispheres, which appear as their concave surface would be seen by an eye placed at the opposite pole. In this way the meridians become straight lines diverging from the same centre, and the parallels are circles having the same common centre.

The following is the method of constructing a map of the world, on the plane of a meridian, according to the globular projection. (See fig. 17).

About the centre C, with any radius as CB, describe a circle, representing the meridian that is to form the plane of the hemisphere. Draw the diameters NS, and AB, crossing each other at right angles, and the former of these will be the central meridian, and the latter the equator. Divide each semidiameter into nine equal parts, and divide each quadrant of the circle also into nine equal parts, each of which will be equal to 11°. If the scale of the map be sufficiently large, each of these may again be divided into ten equal parts or degrees. The next object is to describe the meridians passing through every 10° of the equator. Suppose we are to draw the meridian of 80° west of Greenwich. We have here three points given, the two poles and the point 80° on the equator, and it is easy to describe a circle that shall pass through these three points. This arch will be the meridian. The method of drawing a circle through any three points is, in this case, as follows. About the centre S, with the radius SC, describe a circular arch, as XX; and about the centre N, with the same radius, describe the arch ZZ; then about the centre 80°, with the same distance, describe arches 1, 1, 2, 2, crossing the former, and draw lines from 2 to 1 on each side of AB, crossing each other, and AB produced, in D. D is the centre of the circular arc, representing the meridian of 80° west from Greenwich; and with the same radius the meridian of 140° west longitude may be drawn. All the other meridians are to be drawn in a similar manner, by describing a circular arch through three points N, S, and the required degree. (See GEOMETRY.)

For describing the parallels, suppose that of 60° N. Lat.; about the centre O, with any radius, describe the circle FGH, and about the points 60°, 60°, in the primitive circle, with the same distance, describe the arcs ee, dd, cutting the circle FGH: through the points of intersection draw straight lines, and the point where these lines meet in NS produced, as in I, is the centre of the arch that will represent the parallel of 60°. The other parallels are drawn in a similar manner, observing that the first circle, such as FGH, must have for its centre that point in the central meridian through which the parallel is to be drawn. Fig. 18. represents this projection.

Principles and Practice projection with all the meridians and parallels completed.

If the map is very large, and the paper on which it is to be drawn does not admit of so many circles, the centres of the meridians and parallels are more easily found in the following manner. Having divided the semi-diameters and quadrants, each into 9 equal parts, find, from a scale of equal parts, the length of the half chord of each arc, and the versed sine of half the same arc; then add together the square of the half chord, and the square of the versed sine, and divide the sum by the versed sine; the quotient is equal to the diameter, and $\backslash frac\{1\}\{2\}$ of this to the radius of the circle required. In this manner the radii of all the meridians and parallels may be found.

As, in drawing maps on a large scale, compasses of an ordinary size will not answer for describing the circular arcs, it is convenient to have some other mechanical contrivance for this purpose; and it is found that a thin flexible ruler of tough wood, called a bow, may be so bended as to form a curve, very nearly circular, that will pass through the three points that are to determine the meridian or parallel. In this way the circles on maps on a large scale are usually drawn by engravers and students of geography; and where the circle is of very large radius, the method is sufficiently accurate; but it ought by no means to be employed where compasses of a proper size can be procured, or conveniently used.

The following is the method given by Dr Hutton, for describing a globular projection of the earth on the plane of the equator. For the north or south hemispheres draw AQBE, for the equinoctial (fig. 19.), dividing it into the four quadrants EA, AQ, QB, and BE; and each quadrant into 9 equal parts, representing each $10^\backslash circ$ of longitude; and then from the points of division, draw lines to the centre C, for the circles of longitude. Divide any circle of longitude, as the first meridian EC, into 9 equal parts, and through these points describe circles from the centre C, for the parallels of latitude, numbering them as in the figure. In this method equal spaces on the earth are represented by equal spaces on the map, as nearly as any projection will bear; for a spherical surface can in no way be represented exactly upon a plane. Then the several countries of the world, seas, islands, sea-coasts, towns, &c. are to be entered in the map, according to their latitudes and longitudes.

To draw a Map of any particular Country.

110
Construction of particular maps.

There are three methods of doing this.

1st, For this purpose its extent must be known as to latitude and longitude; as suppose Spain, lying between the north latitudes $36^\backslash circ$ and $44^\backslash circ$, and extending from $10^\backslash circ$ to $25^\backslash circ$ of longitude, so that its extent from north to south is $8^\backslash circ$, and from east to west $15^\backslash circ$.

Draw the line AB for a meridian passing through the middle of the country (fig. 20.), on which set off $8^\backslash circ$ from B to A, taken from any convenient scale; A being the north and B the south point. Through A and B draw the perpendiculars CD, EF, for the extreme parallels of latitude. Divide AB into eight parts, or degrees, through which draw the other parallels of latitude parallel to the former.

For the meridians, divide any degree in AB into 60

equal parts, or geographical miles. Then, because the length in each parallel decreases towards the pole, from the table shewing this decrease given in p. 514, take the number of miles answering to the latitude of B, which is $48\backslash frac\{1\}\{2\}$ nearly, and set it from B, seven times to E, and six times to F; so is EF divided into degrees. Again, from the same table take the number of miles of a degree in the latitude A, viz. $43\backslash frac\{1\}\{2\}$ nearly; which set off from A, seven times to C, and six times to D. Then from the points of division in the line CD, to the corresponding points in the line EF, draw so many right lines for the meridians. Number the degrees of latitude up both sides of the map, and the degrees of longitude on the top and bottom. Also in some vacant place make a scale of miles, or of degrees, if the map represent a large part of the earth; to serve for finding the distances of places upon the map.

Then make the proper divisions and subdivisions of the country; and having the latitudes and longitudes of the principal places, it will be easy to set them down in the map; for any town, &c. must be placed where the circles of its latitude and longitude intersect. For instance, Gibraltar, whose latitude is $36^\backslash circ\; 11\text{'}$, and longitude $12^\backslash circ\; 27\text{'}$, will be at G; and Madrid, whose latitude is $40^\backslash circ\; 10\text{'}$, and longitude $14^\backslash circ\; 44\text{'}$, will be at M. In the same manner the mouth of a river may be set down; but to describe the whole course of the river, the latitude and longitude of every turning, and of the towns and bridges by which it passes, must also be marked down. The same is necessary for woods, forests, mountains, lakes, castles, &c. The boundaries are described by setting down the remarkable places on the sea coast, and drawing a continued line through them all. This method is very proper for small countries.

2d Method. Maps of particular places are but portions of the globe, and may therefore be drawn in the same manner as the whole globe, either by the orthographic or stereographic projection of the sphere. But in partial maps a more easy method is as follows. Having drawn the meridian AB in the last figure, and divided it into equal parts as before, draw lines through all the points of division; put them together to AB, to represent the parallels of latitude. Then to divide these, set off the degrees in each parallel; diminish after the manner directed for the two extreme parallels CD and EF, and through all the corresponding points draw the meridians, which will be curved lines; these were right lines in the last method, because only the extreme parallels were divided according to the table. This method is proper for a large tract, as Europe, &c. in which case the parallels and meridians need be drawn only through every $5^\backslash circ$ or $10^\backslash circ$. This method is much used in drawing maps, as all the parts are nearly of their due magnitude, except being a little distorted towards the outside, from the oblique intersection of the meridians and parallels.

3d Method. Draw PB of a convenient length, for a meridian; divide it into nine equal parts, and through the points of division, describe as many circles for the parallels of latitude, from the centre P, which represents the pole. Suppose AB (fig. 21.) the height of the map; then CD will be the parallel passing through the greatest latitude, and EF will represent the equator. Divide the equator EF into 9 equal parts of the same size as those in AB, both ways beginning AB; divide

divide also all the parallels into the same number of equal parts, but lesser, in proportion to the numbers for the several latitudes, as directed in the last method for the rectilinear parallels. Then through all the corresponding divisions draw curved lines, which will represent the meridians, the extreme meridians being EC and FD. Lastly, Number the degrees of latitude and longitude, and place a scale of equal parts, either in miles or degrees, for measuring distances.

When the place of which a map is to be made is but small, as when a county is to be delineated, the meridians will be so nearly parallel to one another, and the whole will differ so little from a plane, that the map may be laid down in a much more easy manner than what is given above. It will be here sufficient to measure the distances of places in miles, and note them down in a plane rectangular manner. The method of delineating such partial maps is the province of the surveyor. See SURVEYING.

Mercator's projection is chiefly confined to charts for the purposes of navigation. In this projection the meridians, parallels, and rhumbs, are all straight lines; but instead of the degrees of longitude being everywhere equal to those of latitude, as is the case in plain charts, the degrees of latitude are increased as we approach towards either pole, being made to those of longitude in the proportion of radius to the sine of the distance from the pole, or cosine of the latitude, or, what is the same thing, in the ratio of the secant of the latitude to radius. Hence all the parallel circles are represented by equal and parallel straight lines, and all the meridians are parallel lines also; but these increase indefinitely towards the poles.

From this proportional increase of the degrees of the meridian, it is evident that the length of an arc of the meridian beginning at the equator, is proportional to the sum of all the secants of the latitude; or that the increased meridian bears the same proportion to its true arc as the sum of all the secants of the latitude to as many times the radius. The increased meridian is also analogous to a scale of the logarithmic tangents, though this is not at first very evident. It is not certain by whom this analogy was first discovered, but the discovery appears to have been made by accident. It was first published and introduced into the practice of navigation by Mr Henry Bond, by whom this property is mentioned in an edition of Norwood's Epitome of Navigation, printed about 1645. This analogy, though it had been found true by actual measurement, was not accurately demonstrated. Nicholas Mercator offered to disclose, for a sum of money, a method which he had discovered for demonstrating it; but this was not accepted, and the demonstration was, we believe, never disclosed. See Nicholas MERCATOR. About two years after, however, the demonstration was again discovered, and published by James Gregory.

The meridian line in Mercator's chart is a scale of logarithmic tangents of the half colatitudes. The differences of longitude on any rhumb, are the logarithms of the same tangents, but of a different species; those species being to each other as the tangents of the angles made with the meridian. Hence any scale of logarithmic tangents is a table of the differences of longitude, to several latitudes, upon some one determinate rhumb; and therefore as the tangent of the angle of such a rhumb

is to the tangent of any other rhumb, so is the difference of the logarithms of any two tangents, to the difference of longitude on the proposed rhumb, intercepted between the two latitudes, of whose half complements the logarithmic tangents were taken.

It was the great study of our predecessors to contrive such a chart in plano, with straight lines, on which all or any parts of the world might be truly set down, according to their longitudes and latitudes, bearings, and distances. A method for this purpose was hinted at by Ptolemy, near 2000 years since, and a general map in such an idea, was made by Mercator: but the principles were not demonstrated, and a ready way shown of describing the chart, till Wright explained how to enlarge the meridian line by the continual addition of secants, so that all degrees of longitude might be proportional to those of latitude, as on the globe; which renders this chart, in several respects, far more convenient for the navigator's use, than the globe itself, and which will truly shew the course and distance from place to place, in all cases of sailing.

For further particulars respecting the construction, and for the use of charts, see NAVIGATION.

In choosing maps, it is proper to examine particularly whether the curved lines of those that ought to have the meridians and parallels arcs of circles be truly circular. If the map is composed of more than one sheet, the sheets should be so joined together as that the corresponding meridional lines and parallels be each in one continued line. The colours in painted maps, as was observed with respect to globes, should be fine and transparent, and not laid on too thickly.

Maps folded for the pocket answer very well for travelling, in so far as they point out the relative situation of places; but, owing to the intervals at which the parts are pasted on the canvass, the distances between places cannot be ascertained with any degree of accuracy.

SECT. III. Of the Use of Maps.

Maps are of great utility in the study of geography and history; and if they are accurately drawn, many of the problems that are usually performed on the globes, may be solved mechanically by means of maps.

In consulting a map, it is not sufficient to find out in it the name of the place of which you desire to know the situation, although this is frequently all at which the consulter of a map aims: it is, besides, proper for the student to inform himself respecting the relative position of the place, with regard to its vicinity to other places; its bearings and distance from the principal places in the same or neighbouring districts; whether it is near the sea shore, and is near a convenient harbour; whether it be seated on some principal river, and on what side of the river; whether it is in the neighbourhood of a considerable canal; whether it be near a lake, mountain, forest, &c. and many other little particulars that will readily suggest themselves to an attentive reader.

The problems that are usually performed by means of maps, are the following.

PROBLEM I. To find the latitude and longitude of any given place.

In maps on a large scale, or where the meridians and parallels of latitude are straight lines, the latitude of the place

place may be easily found by stretching a thread over the place, so that it may cross the same degree of latitude on each side of the map; and the degree crossed will be the latitude required. Or, with a pair of compasses measure the shortest distance of the place from the nearest parallel, and apply this distance to either side of the map, so as to keep one point of the compasses on the same parallel; then the other point will show the degree of latitude as measured on the graduated margin, counting from the parallel north or south, according as the place is in north or south latitude.

The longitude of the place may be found in a similar manner, by stretching the thread over the place, or laying a ruler across it, so as to cut the same degree of longitude on the top and bottom of the map, and that is the degree required.

The above methods answer very well in plain charts or in maps of counties; but when the meridians and parallels are curved lines, we must find how often the distance of the place, measured by the compasses from the nearest parallel, will reach the next parallel in a straight direction, and from thence the latitude may be found with sufficient exactness. Thus, suppose we are required to find the latitude of Berlin, the capital of Prussia. The nearest parallel is that of $50^\{\backslash circ\}$ north latitude; the distance of Berlin from this parallel will reach the parallel of $60^\{\backslash circ\}$ in four times, measuring on the map of Europe. The fourth part of ten, or two and a half, added to 50, gives the latitude required, or $52\backslash frac\{1\}\{2\}$.

To find the longitude on such maps, measure how often the distance of the place from the nearest meridian will reach the next meridian. Thus, in the same instance, the distance of Berlin from the meridian of 10, which is the nearest towards the east, taken three times, will extend a little beyond the meridian of 20. Add to 10 the third part of this distance, which is about three and a half, and we have $13^\{\backslash circ\}\; 30\text{'}$ for the longitude of Berlin east from London.

PROBLEM II. The latitude and longitude of a place being given; to find the place on the map.

Where the meridians and parallels are straight lines, this is done by stretching one thread from the given latitude on one side of the map to the same latitude on the other side; while another thread is stretched between the corresponding degrees of longitude. The intersecting point of the two threads shows the place required. Thus, suppose we are required to find the place whose latitude is $34^\{\backslash circ\}\; 20\text{'}\; S.$ and longitude $18^\{\backslash circ\}\; 23\text{'}\; E.$ Stretching one thread between the given latitudes, and another between the given longitudes, we shall find that they cross over the Cape of Good Hope, which is therefore the place required.

When the meridians and parallels are curved lines, the most accurate way will be to describe a circle of latitude through the given degree of latitude on each side, and a circle of longitude through the corresponding degrees of longitude, and the intersection of these circles will show the place. An easier method will be, knowing between what two parallels of latitude and longitude the place lies, and consequently by what four lines it is bounded, to find the place by trial, by considering the proportional distance of it from each line.

PROBLEM III. The latitude of a place being given; to find all those places on the same map that have the same latitude.

If a parallel of latitude happen to be drawn on the map through the given place, this problem is easily solved, by tracing along the parallel, and seeing what other places it passes through. If a parallel is not drawn through the given place, take with a pair of compasses the distance of the place from the nearest parallel; then keeping one foot on the parallel, and the other in such a position as to describe a line parallel to the parallel of latitude, move the compasses, and all the places over which the point that is not on the parallel passes, have the same latitude with the given place.

This method will not succeed in maps on which a large tract of country is delineated on a small scale.

PROBLEM IV. Given the longitude of a place; to find on the map all those places that have the same longitude.

Find the longitude of the given place, and if a meridian passes through it, observe all the places that lie under this meridian; or, if a meridian does not pass through the place, find by the compasses, as in the last problem, those places that are situated at the same parallel distance with the given place from the nearest meridian. These places have nearly the same longitude with the given place.

PROBLEM V. To find the antecci of a given place.

Find the latitude and longitude of the place by Problem I. and find another place of the same longitude, whose latitude is equal to that of the former, but in a contrary direction. The inhabitants of this latter place are the antecci to the former.

Ex. Suppose a ship to be in the Indian ocean, in lat. $13^\{\backslash circ\}\; S.$ and long. $80^\{\backslash circ\}\; E.$ it is required to find the antecci to her present situation? Ans. The place which has nearly the same longitude, and an equal latitude in a contrary direction, viz. $13^\{\backslash circ\}\; N.$ is Madras.

PROBLEM VI. To find the pericci of a given place.

Find the longitude of the given place, and subtract it from $180^\{\backslash circ\}$: the remainder will be the longitude in an opposite direction of the pericci. Then find a place having an equal longitude with this last, and having the same latitude with that of the given place: this latter is the situation required.

Ex. It is required to find the pericci to the inhabitants of the gulf of Siam. Ans. The longitude of Siam is $100^\{\backslash circ\}\; 30\text{'}\; E.$ which, subtracted from $180^\{\backslash circ\}$, leaves $79^\{\backslash circ\}\; 10\text{'}\; W.$ Now, the place that has this longitude, and the same latitude with Siam, viz. about $14^\{\backslash circ\}\; N.$ is the isthmus of Darien.

PROBLEM VII. To find the antipodes of a given place.

This problem is solved on maps in the same manner as on the globe.

PROBLEM VIII. Having the hour at any place given; to find what hour it is in any part of the world.

Find the difference of longitude between the two places, and reduce this to its equal value in time, by

Nº 65. Add this value to the given hour, if the place where the time is required be to the eastward of the given place, and the sum is the time required. If the place at which the time is required lie to the westward of the given place, subtract the difference of longitude in time from the given hour, and the difference is the time sought.

Note.—If, after adding, the sum is found greater than 12, 12 must be cancelled, and the hours must be changed from A. M. to P. M. and vice versa; and if, on subtracting, the difference in time between the two places happens to be greater than the given hour, 12 must be added to the given hour, and the hours changed as before mentioned.

Ex. Suppose it to be at present 9 A. M. at Lisbon, what time of the day is it at Pekin in China? Ans. The difference of longitude between Pekin and Lisbon is $125^\{\backslash circ\}\; 33\text{'}$, which reduced to time gives 8 hours 22 minutes; and since Pekin lies to the east of Lisbon, this must be added to 9, the given hour, giving a sum of 17 hours, 22 minutes; but as this is greater than 12, we must take 12 away, and the difference, 5 hours 22 minutes, changed from morning to afternoon hours, is the time required. It is therefore 22 minutes past five P. M. at Pekin.

PROBLEM IX. To find those places in the torrid zone to which the sun is vertical on any given day.

Find in an ephemeris, or nautical almanack, the sun's declination for the given day; then observe, in the map of the world, all those places which lie under that parallel of latitude, which is the same with the declination, and these will be the places required.

Ex. It is required to find at what places the sun will be vertical on the 20th of March and 23d of September? Ans. The sun's declination on the 20th of March, is $19^\{\backslash circ\}$ S. and on the 23d of September $6^\{\backslash circ\}$ N. Now the principal places that lie near the parallel of $19^\{\backslash circ\}$ S. and $6^\{\backslash circ\}$ N. are the island of St Thomas, the middle part of the islands of Sumatra and Borneo; the Galapagos isles, and Quito in South America.

The Analecta, or Orthographic Projection delineated in Plate CCXXXV. will solve many of the most curious problems, and with the assistance of maps will be almost equivalent to a terrestrial globe. The parallel lines drawn on this figure represent the degrees of the sun's declination from the equator, whether north or south, amounting to $23\backslash frac\{1\}\{2\}$ nearly. On these lines are marked the months and days which correspond to such and such declinations. The size of the figure does not admit of having every day of the year inserted; but by making allowance for the intermediate days, in proportion to the rest, the declination may be guessed at with tolerable exactness. The elliptical lines are designed to shew the hour of sunrising or sunsetting before or after six o'clock. As 60 minutes make an hour of time, a fourth part of the space between each of the hour-lines will represent 15 minutes; which the eye can readily guess at, and which is as great exactness as can be expected from any mechanical invention, or as is necessary to answer any common purpose. The circles drawn round the centre at the distance of 11$\backslash frac\{1\}\{2\}$ each, shew the point of the compass on which the sun rises and sets, and on what point the twilight begins and ends.

In order to make use of this analemma, it is only necessary to consider, that, when the latitude of the place and the sun's declination are both north or both south, the sun rises before six o'clock, between the east and the elevated pole; that is, towards the north, if the latitude and declination are north; or towards the south, if the latitude and declination are south. Let us now suppose it is required to find the time of the sun's rising and setting, the length of the days and nights, the time when the twilight begins and ends, and what point of the horizon the sun rises and sets on, for the Lizard point in England, Frankfort in Germany, or Abbeville in France, on the 30th of April. The latitude of these places by the maps will be found nearly $50^\{\backslash circ\}$ N. Place the moveable index so that its point may touch $50^\{\backslash circ\}$ on the quadrant of north latitude in the figure; then observe where its edge cuts the parallel line on which April 30th is written. From this reckon the hour-lines towards the centre, and you will find that the parallel line is cut by the index nearly at the distance of one hour and 15 minutes. So the sun rises at one hour 15 minutes before six, or 45 minutes after four in the morning, and sets 15 minutes after seven in the evening. The length of the day is 14 hours 30 minutes. Observe how far the intersection of the edge of the index with the parallel of April 30th is distant from any of the concentric circles, which you will find to be a little beyond that marked two points of the compass, and this shews that on the 30th of April the sun rises two points and somewhat more from the east towards the north, or a little to the northward of east-north-east, and sets a little to the northward of west-north-west. To find the beginning and ending of the twilight, take from the graduated arch of the circle $17\backslash frac\{1\}\{2\}$ degrees with a pair of compasses; move one foot of the compasses extended to this distance along the parallel of April 30th, till the other just touches the edge of the index, which must still point at 50. The place where the other foot rests on the parallel of April 30th, then denotes the number of hours before six at which the twilight begins. This is somewhat more than three hours and a half, which shews that the twilight then begins soon after two in the morning, and likewise that it begins to appear near five points from the east towards the north. The uses of this analemma may be varied in a great number of ways; but the example just now given will be sufficient for the ingenious reader.

SECT. IV. Of the Origin and Progress of Maps.

THE first map of which we have any certain record, is that of Anaximander, about 560 years before the Christian era. This is mentioned by Strabo, book i. and is supposed to be that referred to by Hipparchus, under the name of the ancient map.

It has been alleged, that Sesostris, king of Egypt, on his return from his boasted expedition, after having traversed great part of the earth, recorded his march in maps, of which he gave copies, not only to the Egyptians, but to the Scythians, to the great admiration of both people. This is the relation of Eustathius; but M. Montucla considers it as a very improbable story, and thinks that the invention of maps cannot be dated Hist. de prior to Anaximander*. Some have supposed that the Maibenz. Jews laid down the holy land in a map, when they dif-
tributed P. 589.

This historical map, labeled Fig. 1, depicts the Bay of Bengal and the surrounding maritime regions. Key features include the Bay of Bengal (A), the Strait of Malacca (C), and the Cape of Demerary. The map shows the Equinoctial Line and the Mouth of a River. It also includes the Mouth of the Nile, the Lake of Victoria, and the city of Metropolis. A scale of nautical miles is provided at the bottom right.

This historical map, labeled Fig. 2, provides a detailed view of the Bay of Bengal and the surrounding regions. It shows the Bay of Bengal (A), the Strait of Malacca (C), and the Cape of Demerary. The map includes the Equinoctial Line and the Mouth of a River. It also shows the Mouth of the Nile, the Lake of Victoria, and the city of Metropolis. A compass rose with the text 'POINTS OF THE COMPASS' is located in the center, and a scale of nautical miles is provided at the bottom right.

An armillary sphere is depicted, consisting of a central sphere with a series of concentric rings (equatorial, ecliptic, and meridians) that represent the celestial sphere. The sphere is mounted on a stand with a base and a vertical support. Numerous points on the rings are labeled with capital letters: A, B, C, D, E, F, G, H, I, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z. The stand has a circular base and a vertical post with a horizontal arm supporting the sphere.

A geometric diagram of a sphere, likely representing a celestial or terrestrial sphere. It shows a vertical axis with points I at the top and S at the bottom. A horizontal line passes through the center C, with points D and B at the ends. A curved line representing a celestial or terrestrial circle is shown, with points A and E on it. The diagram includes various lines and points labeled with letters and numbers, such as 1°, 2°, 3°, 4°, 5°, 6°, 7°, 8°, 9°, 10°, 11°, 12°, 13°, 14°, 15°, 16°, 17°, 18°, 19°, 20°, 21°, 22°, 23°, 24°, 25°, 26°, 27°, 28°, 29°, 30°, 31°, 32°, 33°, 34°, 35°, 36°, 37°, 38°, 39°, 40°, 41°, 42°, 43°, 44°, 45°, 46°, 47°, 48°, 49°, 50°, 51°, 52°, 53°, 54°, 55°, 56°, 57°, 58°, 59°, 60°, 61°, 62°, 63°, 64°, 65°, 66°, 67°, 68°, 69°, 70°, 71°, 72°, 73°, 74°, 75°, 76°, 77°, 78°, 79°, 80°, 81°, 82°, 83°, 84°, 85°, 86°, 87°, 88°, 89°, 90°, 91°, 92°, 93°, 94°, 95°, 96°, 97°, 98°, 99°, 100°, 101°, 102°, 103°, 104°, 105°, 106°, 107°, 108°, 109°, 110°, 111°, 112°, 113°, 114°, 115°, 116°, 117°, 118°, 119°, 120°, 121°, 122°, 123°, 124°, 125°, 126°, 127°, 128°, 129°, 130°, 131°, 132°, 133°, 134°, 135°, 136°, 137°, 138°, 139°, 140°, 141°, 142°, 143°, 144°, 145°, 146°, 147°, 148°, 149°, 150°, 151°, 152°, 153°, 154°, 155°, 156°, 157°, 158°, 159°, 160°, 161°, 162°, 163°, 164°, 165°, 166°, 167°, 168°, 169°, 170°, 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A map of the world showing latitude and longitude lines. The map is a projection of the sphere, with latitude lines (parallels) and longitude lines (meridians). The poles are labeled P at the top and N at the bottom. A horizontal line is labeled C in the center. A point A is marked on the left side of the map. The map is a projection of the sphere, with latitude lines (parallels) and longitude lines (meridians).

A circular diagram with concentric circles and radial lines, likely representing a celestial or terrestrial sphere. The diagram is divided into segments by radial lines, and the outer edge is marked with degrees. The center is labeled C. Points A, B, D, E, F, G, H, I, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z are marked around the perimeter. The diagram is a projection of the sphere, with latitude lines (parallels) and longitude lines (meridians).

An Analemma, Shewing the time of Sun rising & Sun setting, the length of the Days & Nights, and the point of the Compass on which the Sun rises & sets, for every Degree of Latitude, and for every Degree of the Sun's North & South declination.

The diagram is a circular Analemma with concentric circles and radial lines. A large white pointer is positioned at the center, pointing towards the upper right. The diagram is divided into four quadrants by a vertical and horizontal axis.

Outer Circles:

• Top arc: "In this scale the North latitude of the Place is to be found." with degree markings from 0 to 90.
• Bottom arc: "The line that the Sun's Latitude is to be found." with degree markings from 0 to 90.
• Left arc: "The line that the Sun's Longitude is to be found." with degree markings from 0 to 360.
• Right arc: "The line that the Sun's Declination is to be found." with degree markings from 0 to 90.

Inner Circles (Compass Points):

• Seven Points of the Compass.
• Six Points of the Compass.
• Five Points of the Compass.
• Four Points of the Compass.
• Three Points of the Compass.
• Two Points of the Compass.
• One Point of the Compass.

Radial Lines:

• Left side: "Hours of Sun rising after Six in North Latitude." with Roman numerals I, II, III, IV, V.
• Right side: "Hours of Sun rising before Six in North Latitude." with Roman numerals I, II, III, IV, V.

Text Labels:

• Top: "North Pole" at the top of the vertical axis.
• Bottom: "South Pole" at the bottom of the vertical axis.
• Center: "Center of the Compass."

Table of Sun's Positions (Left Side):

Table of Sun's Positions (Right Side):

This is a historical world map, likely from the 18th or 19th century, presented in a circular projection. The map is divided into four quadrants by a vertical and horizontal line. The continents are labeled with their names in capital letters, such as AMERICA, EUROPE, ASIA, and AUSTRALIA. The oceans are labeled as ARCTIC OCEAN, ATLANTIC OCEAN, INDIAN OCEAN, and PACIFIC OCEAN. The map includes a grid of latitude and longitude lines, with the Arctic Circle and Antarctic Circle marked. Numerous islands and smaller landmasses are labeled, including the British Isles, the continent of North America, Europe, Asia, Africa, and Australia. The map also shows the coastline of the world, with many bays and straits labeled. The map is framed by a circular border with a grid of latitude and longitude lines.

THE
WORLD

1770

1770

A
Chart
of
the
WORLD
ON
Mollweide's Projection

PART OF OLD GREENLAND

BAPPIIN'S BAY (doubtful)

DANIEL'S STRAIT

WEST IND. GREENLAND

RUSSIA

AMERICA

ATLANTIC OCEAN

SOUTH AMERICA

INDIAN OCEAN

Pacific Ocean

Atlantic Ocean

Tropic of Capricorn

Equator

Latitude of Capricorn

Chart
of
THE WORLD
Mercator's Projection

W. H. M. 1791

Edw. Owen. Washington. 1791.

Principles and Practice. Principles attributed the different portions to the nine tribes at Shiloh; a supposition which is derived from Joshua's account, that they were sent to walk through the land, and that they described it in seven parts in a book. Josephus also relates, that when Joshua sent people from the different tribes to measure the land of promise, he sent with them men well skilled in geometry. All this, however, is no proof that these persons drew a sketch of the country, according to our idea of a map; but probably only wrote down, for the satisfaction of their employers, the extent, boundaries, and general characteristics of the divisions of the land.

Herodotus has given a minute description of a map constructed by Arilagoras, tyrant of Miletus, an abridgement of which will serve to give some notion of the maps of those times. It was drawn upon brass or copper, and seems to have been merely an itinerary containing the route through the countries which were to be traversed in a march which Arilagoras proposed to Cleomenes, king of Sparta, for the purpose of attacking the king of Persia at Susa, that he might thus assist in restoring the Ionians to their liberty. The rivers Halis, Euphrates, and Tigris, which, according to Herodotus, must have been crossed in that expedition, were laid down in this map; and it contained one straight line, called the royal road or high way, which comprehended all the stations or places of encampment, from Sardis, the beginning of the route, to Susa, a distance of 13,500 stadia, or 1687½ Roman miles of 5000 feet each. The number of encampments in this whole route was 111.

Ptolemy of Alexandria, the celebrated geographer mentioned in N° 21, constructed maps to illustrate his description of places, and these are the first that have regular meridians and parallels, the better to define and determine the situation of places. Ptolemy acknowledges that his maps, with the addition of some improvements of his own, the principal of which was certainly the introduction of meridians and parallels, were copied from previous maps made by Marianus Tyrius, &c. They are, however, often very inaccurate.

According to Athenæus, a work which seems to have contained maps, was written by Baeton, under the title of Alexander's march; and a work on the same subject is mentioned as the production of Amyntius. We are informed by Pliny, that this Baeton was one of the surveyors of Alexander's marches; and he quotes the exact number of miles of these marches, according to Baeton's mensuration, and confirms their authenticity by the letters of Alexander. Pliny also remarks, that a copy of this conqueror's surveys was given by Zenobius, his treasurer, to the geographer Patrocles, who was admiral of the fleets of Seleucus and Antiochus.

Among the most celebrated of the ancient maps, are the Peutingerian tables, so called, because published by Peutinger of Augsberg. These tables contain an itinerary of the whole Roman empire; all places except seas, wood, and deserts, being laid down according to their measured distances, though without any mention of latitude, longitude, or bearing. A particular description of this monument of antiquity is given in the 18th volume of the History of the Academy of Inscriptions, and in the History of the Academy of Sciences for 1761, from which M. Montucla has drawn up the following account. The map of Peutinger, as it is in the

original in the imperial library, is exactly one French foot in height, and 20 feet eight inches in length, according to measures taken by Buache, from a copy of the splendid edition given by Scheele in 1753. It comprehends the whole extent of the Roman empire, from Constantinople to the ocean, and from the shores of Africa to the northern parts of Gaul; but the table which it affords of this vast extent of country is by no means calculated to give us an idea of its figure, since the 35° of longitude which it comprehends, occupy 20 feet 8 inches, while the 13° of latitude are comprised within the space of one foot; thus the countries represented are so disfigured, that the Mediterranean appears only like a broad river, and all the countries are so distorted, towards the north and south, that they cannot be recognized.

Most of those who have seen this ancient map, have considered it as the rude and bungling work of a man little conversant with geography, and still less so with mathematics; but Edmund Brutz considers the distortion of this map as similar to what we see in some pieces of perspective, and that it ought to be examined from some certain near point in order to perceive the objects in their natural proportion.

Buache supposed long ago, that this map was constructed with more scientific skill than it appears to be at the first glance; and that the apparent irregularities which we observe in it, might have been introduced designedly, for the purpose of deriving greater advantages as to what was intended for the principal object. In fact, as the Roman routes extended almost entirely from east to west, they paid more attention to the measures in this direction than those between north and south; and the map in this way might have had the greater convenience of being more easily rolled up, and consequently more portable.

Thus far Buache hazarded no more than conjecture; but a labour undertaken by him with a very different view, led him to the true design of the map of Peutinger. He had been tracing a scale of climates, and of the length of the days and nights, for the purpose of attaching it to small maps of the different countries of Europe. As the space occupied by the scale was pretty much extended in height, but had very little breadth, he formed the idea of drawing a kind of map upon two scales, one pretty much extended for the latitude, and the other very much contracted for the longitudes, preserving the hollows of the coasts and boundaries of each state. As this disposition of his map strangely disfigured the countries which it was intended to represent, he was led to imagine that this map might be the reverse of that of Peutinger. This was sufficient to engage him to construct another map upon the same principle; but in which the scale of longitudes was much greater than that of the latitudes. He then saw that he had been right in his supposition, and that the map which he had last constructed had a considerable resemblance to that of Peutinger. This latter is in fact only a plain chart, constructed upon two scales, of which that of the longitudes is very great, and that of the latitudes much smaller.

One difficulty alone arose. By supposing that he observed in this map a custom at present established among geographers, of representing the meridians by lines drawn perpendicular to the base of the chart, and the

Principles and Practice. parallels to the equator by straight lines drawn parallel to this same base, Bunche found a considerable error. The bottom of the gulf of Venice and Rome did not then appear, as they ought to do, under the same meridian. He soon, however, saw the solution of this difficulty. The method of drawing the meridians parallel to the sides of the chart, is a matter of pure agreement, and had probably not been observed in the map of which we are speaking. The ancient Roman geographers having considered that Italy was naturally divided by the Appenines, according to its length, into two parts that were nearly equal, had therefore delineated the length of Italy from Trent to the end of the peninsula, parallel to the lower margin of the map, and had afterwards arranged the other parts which the map was to contain, conformably to this disposition; and as the length of Italy is not in a direction parallel to the equator, it would happen necessarily that the meridians and parallels, if they had been drawn on this map, would have been parallel neither to the sides nor to the lower margins of the map, and that the vertical line passing through Rome must intersect the gulf of Venice at about the middle: but this line is not a meridian.

Thus, this map is not so rude a work as has been imagined, but has been entirely constructed according to rule; and it even appears that the author had employed pretty good materials in its compilation, as the positions are laid down in a manner that differs little from modern observations.

* M. Mercator, tom. iv. p. 599. From the time of Ptolemy till about the 14th century, no new maps were published; and the first maps of any esteem among the moderns were constructed by Mercator, to whom we are indebted for the projection according to which marine charts are constructed. Mercator was followed by Ortelius, who undertook to construct a new set of maps with the modern divisions of countries and names of places, for want of which the maps of Ptolemy were become almost useless. After Mercator and Ortelius, many others published maps, which were chiefly copied from those above mentioned, till about the middle of the 17th century, when Blaeu published his large atlas, or Cosmographie blaviane, in which is a pretty accurate description of the earth, the sea, and the heavens, comprised in 12 folio volumes. About the same time an atlas in two folio volumes was published in France by M. Sanson, the maps of which are in general very correct, containing many improvements of the travellers of those times. The maps of Blaeu and Sanson were copied with little variation both in England, France, and Holland, till from later observations De Lille, Robert, Wall, &c. published still more accurate and copious sets of maps.

The works of recent travellers and navigators have considerably improved the construction and accuracy of our maps and charts; but there is still much to be done, especially with respect to trigonometrical surveys, before any high degree of correctness can be acquired. Among the latest maps and charts, those constructed by Mr. Arrowsmith are in the greatest estimation.

As a collection of good and accurate maps is of the greatest importance in the study of geography and history, we shall here subjoin a list of some of the best modern maps that have been published.

Those maps which may be collected for the purpose of forming an atlas, have been arranged under three

heads, according to their size, or the extent of their scale. 1st, Those which consist of more than six sheets, such as De Bouge's map of Europe in 50 half sheets; and Cassini's map of France in 183 sheets. 2dly, Those from six to four sheets, to which class belong several maps of kingdoms. And, 3dly, Those from one sheet to four, which is the smallest size that can answer the purpose of an atlas. We shall briefly notice the best maps of each size.

Planispheres, or Maps of the World.—We know of no very large map of the world that can at present be confidently relied on: the best is that of Mr. Arrowsmith in four sheets; and Faden has published very good maps in one sheet.

Maps of Europe.—1st size. That of De Bouge, published at Vienna, or that by Sotzmann in 16 sheets, which is the better of the two. 2d size. Arrowsmith's in four sheets. 3d size. That by Faden in one sheet.

Maps of England.—I. The trigonometrical surveys of the counties, published by Lindley and Gardner, and by Faden. II. Cary's atlas of the counties, and his England and Wales in 81 sheets. III. Faden's map in one sheet.

Maps of Wales.—I. That of Evans in nine sheets. III. The maps in Pennant's Tours, and Evans's Cambrian Itinerary.

Maps of Scotland.—I. The surveys of the several counties. II. Ainslie's nine sheet map. III. An excellent map by General Roy, and Ainslie's reduced map in one sheet.

Maps of Ireland.—I. Surveys of counties. III. A valuable map by Dr. Beaufort in two sheets, or Faden's in one sheet.

Maps of France.—I. Cassini's, mentioned above, and the atlas nationale in 85 sheets. III. Faden's one sheet map, and a map, in departments, by Bellycine in four sheets.

Maps of the Netherlands.—I. Ferrari's map in 25 sheets. II. Atlas de Département Belgique. III. Ferrari's map reduced by Faden.

Maps of Holland.—II. Kep's maps of the United Provinces. III. Faden's map of the Seven United Provinces in one sheet.

Maps of Germany.—II. Chauchard's map of Germany. III. A map of the Austrian dominions, in one sheet, by Baron Lichtenstern.

Maps of Prussia.—I. Sotzmann's atlas in 21 sheets. III. Sotzmann's reduced, in one sheet.

Maps of Spain.—Lopez's atlas, not, however, very accurate. II. A map of Spain in nine sheets by Montelle and Chanlaire. III. Faden's map in one sheet.

Maps of Portugal.—II. Geoffry's improved by Rainford, in six sheets. III. De la Rochette's chorographical map in one sheet, published by Faden.

Maps of Italy.—I. The maps of the several states. III. D'Anville's map of Italy improved by De la Rochette, in four sheets, published by Faden.

Maps of Turkey in Europe.—III. Arrowsmith's map of Turkey in two sheets. De la Rochette's map of Greece in one sheet.

Maps of Switzerland.—I. Weiss's atlas, published at Strasbourg in 1800. III. Weiss's reduced map in one sheet.

Maps of Denmark.—I. Maps of the provinces, under the direction of Bygge. III. Faden's maps of Denmark, Sweden, and Norway, in one sheet.

Maps

Maps of Sweden.—I. Atlas of the Swedish provinces, by Baron Hermelin. III. De la Rochette's, by Faden, in one sheet.

Maps of Asia.—The best general map of Asia is that by Arrowsmith in four sheets, published in 1801; and D'Anville's, in six sheets, may still be consulted with advantage.

There are few good maps of the individual countries; but the following are esteemed among the best.

Of China.—D'Anville's atlas, and a map by Arrowsmith.

Of Tartary.—A map by Witzen, in six sheets, and one by De Witt in one sheet.

Of Japan.—Robert's map in one sheet.

Of the Birman Empire.—The maps published in Mr Symes's embassy.

Of Hindostan.—Rennell's map in four sheets. His atlas of Bengal, and his map of the southern provinces.

Of Persia. there is no good modern map; but La Rochette published a beautiful one, to illustrate the expedition of Alexander the Great.

Of Arabia. there are some good partial maps in Niebuhr's journey.

Of the Asiatic Islands. there is an excellent chart by Arrowsmith, in four sheets.

Of Australasia, or New Holland, the best drawing is contained in Arrowsmith's chart of the Pacific ocean.

Maps of Africa.—The best general map of Africa is still that of D'Anville, though some little additions may be made to it, derived from the journeys of Park

and Brown. Major Rennell's partial maps may be consulted with advantage.

Of Abyssinia. there is a good map in Bruce's travels.

Of Egypt, the best maps are that of the Delta by Niebuhr, and that of Lower Egypt by La Rochette.

Of the Mahometan States, the best maps are those by Shaw, and a chart of the Mediterranean in four sheets, by Faden.

Of the Cape of Good Hope, the best is Barrow's survey.

Maps of America.—There is no modern general map of America that can be relied on. The best is that of D'Anville, in five sheets, published in 1746 and 1748.

Mr Arrowsmith has published an excellent map of North America, on a very large scale, but has omitted the Spanish dominions.

Of the United States, the best map is Arrowsmith's in four sheets, published in 1802; and there are very good maps of the individual provinces in Morse's American Geography.

Of the British Possessions in America, besides Arrowsmith's map above mentioned, there is a good map of Upper Canada by Smith, in one sheet.

Of the West India Islands, the best map is that of Jefferys in 16 sheets, from which a smaller one in one sheet has been reduced.

Of South America, the best map is that published by Faden in 1799, in six sheets, from an engraving done at Madrid some years before.

A P P E N D I X.

127
Observe. BEFORE we conclude this article, we must make a few observations on the method to be followed for acquiring or imparting geographical knowledge.

As some knowledge of geography, as well as of chronology, is absolutely necessary, before history can be properly understood, the rudiments of these sciences should be learned, as soon as the capacity of the pupil will allow. It happens fortunately, that some of the most useful parts of geography, those which consider the relative situations, extent and boundaries of countries, with the manners and customs of their inhabitants, are highly interesting; and provided that a knowledge of them be conveyed to a child in a pleasing manner, they are well fitted to interest his curiosity, and awaken his attention. The more scientific parts of geography, and a detailed account of the minute circumstances respecting each country, though extremely useful, and indeed necessary to the more advanced student, may be withheld for a little without any great loss, till his age and judgement permit him to see their utility and application.

In teaching geography to very young children, their chief attention should be directed to those circumstances which are most interesting; and even with this limited view much may be learned at a very early period. For this purpose the disaffected maps that are usually sold at toy shops, may be employed with considerable advantage; but it is to be regretted, that the maps used in preparing these are seldom taken from the most

correct copies. Those works also which, under the disguise of fictitious voyages and travels, are intended to convey a geographical knowledge of various countries, afford a very pleasing and profitable method of instruction. A late work of this kind, by M. Jaufray, entitled the Travels of Rolando, may be advantageously put into the hands of young people; and, as they are further advanced, the travels of Anacharsis the younger by the Abbé Barthelemy will give them considerable information respecting the manners, customs, and historical events of ancient Greece.

When the young student is sufficiently advanced to prosecute the study of geography on a more extensive and scientific plan, it would be desirable that he should begin by reading some elementary treatise on astronomy, such as that of Mr Bonnycaillie, or the Spectacle de la Nature; or, if he has acquired a proper degree of mathematical knowledge, he may read Laplace's Système du Monde, the astronomical part of Robison's Mechanical Philosophy, or the astronomical article in this dictionary.

It may happen, that, from a defect of early education, or want of time, a preliminary course of astronomy cannot be commanded. Still, however, considerable progress may be made in geography, by the mechanical means of maps and globes. The student should, therefore, provide himself with a pair of the best globes, chosen according to the directions laid down in N^o 107; and with a few good maps of those countries which

are most interesting, particularly maps of Europe, Asia, Africa, and North and South America, the British islands, France, Germany, Italy, Russia, and Denmark, which may be collected from the list given at N^o 126.

Being provided with these materials, the student should first read over Chap. I. of Part II. of this treatise, or a similar part of some elementary work in geography. On the elementary principles of geography we would recommend the general principles prefixed to Mr Pattefon's general and classical Atlas; and for teaching the use of the globes, Bruce's Introduction to Geography and Astronomy. For a complete account of modern geography we cannot refer to a better work than that of Mr Pinkerton; and for a combined account of ancient and modern geography, the pupil may have recourse to a work on that subject by Dr Adam of Edinburgh.

After reading over the preliminary part above mentioned, the pupil may go through the second Chapter of Part II. solving all the problems as he goes along on the terrestrial globe; and thus he may proceed progressively through the whole article, leaving that part of Part I. which treats of the history of geography for the last object of his enquiry.

In studying the particular circumstances of each country, the pupil should always have the map of the country before him; and, as he goes along, should trace there the situation of each particular place; of the principal mountains, lakes, the sources and directions of the rivers, the form and bounding of the shores, &c. In his progressive view of particular geography, it will be proper for the pupil to begin with the country in which he resides; and, after having made himself master of that, to proceed successively to those which border on it, or whose connection with it is the most interesting.

Thus an inhabitant of these islands, after having taken a view of EUROPE in general, should make himself acquainted with BRITAIN and IRELAND (by perusing the articles ENGLAND, SCOTLAND, and IRELAND in this Dictionary or in other works); whence he may proceed to FRANCE and its dependencies in the NETHERLANDS, SWITZERLAND, ITALY; thence to GERMANY and the AUSTRIAN territories, PRUSSIA, SWEDEN, DENMARK, and RUSSIA; whence he may return to the south of Europe to SPAIN, PORTUGAL, and TURKEY, &c. After Europe, the United States of AMERICA will probably be found the most interesting; the pupil may therefore study the geography of NORTH AMERICA before that of ASIA. From ASIA he may proceed to AUSTRALASIA and POLYNESIA; thence to AFRICA, and so conclude with SOUTH AMERICA. Nothing will contribute more to the advancement of geographical studies than the construction of maps. If the pupil has time therefore he should early be instructed in this part of the

subject by at first drawing a map of the world according to the directions laid down in N^o 118. then one of Europe, and so of other quarters and countries. In constructing this map, it will be proper first to lay down those places which are near the coast, in order to form the outline of the maritime part of the country, and only the most remarkable places inland, especially those which are situated in the course of the principal rivers. In every map the most prominent features of the country, as the mountains, lakes, rivers, and principal cities and towns, should first be attended to, and from these the pupil may be introduced to the other places in the order of their magnitude or importance.

The most agreeable and interesting method of studying particular geography, after having become acquainted with the elementary principles of the science, would be to peruse the best books of voyages and travels; for from those, where the traveller can be depended upon, the most correct systems of geography are compiled. Many of these, however, are too prolix and particular to be put into the hands of most young people, and a judicious abridgement of the best of them will answer every purpose; and perhaps Dr Mavor's collection may be recommended, as the best of the kind in the English language. For those whose time and convenience will admit of their reading the best writers of voyages and travels, there is no want of such works; and Mr Pinkerton has given at the end of his excellent work, a list of the best in most languages. We shall here only notice a few of the best and latest.

Pennant's Tours in Britain.

Young's Tours in the British Isles.

Saintsond's Travels in England and Scotland.

Young's Travels in France.

Holcroft's Tour in France.

Spallanzani's Travels in the two Sicilies.

Coxe's Travels in Russia, &c.

Pallas's Travels in the Russian empire.

Carr's Northern Summer.

Staunton's Account of China.

Barrow's Travels in China.

Percival's Account of Ceylon.

Symes's Embassy to Ava.

Collins's account of New South Wales.

Bruce's Travels in Abyssinia.

Barrow's Travels in Africa.

Park's Travels in the interior of Africa.

Browne's Travels in Africa.

Sonmini's Travels in Egypt.

Percival's Cape of Good Hope.

Mackenzie's Journey in North America.

Davis's Travels in America.

Mackinnon's Tour in the West Indies; with the voyages of Anson, Byron, Cook, Phipps, Bligh, Wilson, Wallis, La Peyrouse, &c. &c.

Problems on the terrestrial globe.
VII. To find the antipodes, p. 516
VIII. To rectify the globe for the latitude, N^o 88 respecting the sun, 95
IX. To find the sun's place, ib.
X. To find the declination, p. 524
XI. To rectify the globe for the sun's place, ib.
XII. To find the time of sunrise and sunset, ib.
XIII. To find the sun's meridian altitude at a given place, ib.
XIV. To find the sun's altitude for a given hour, ib.
XV. Sun's meridian altitude given, to find the latitude of the place, 525
XVI. To find when the sun is due east or west, ib.
XVII. } To find when the
XVIII. } sun is vertical in
XIX. } the torrid zone, ib.
XX. To find when the sun begins to appear, &c. in the northern frigid zone, ib.
XXI. To find when he begins to shine continually there, 526
XXII. To find the limits of the hour climates, ib.
XXIII. Month climates, ib.
XXIV. To find where the sun is rising, setting, &c. at a given time, ib.
XXV. To find where it is twilight at a given time, 527
XXVI. To find the duration of twilight, &c. ib.
XXVII. To shew the cause of day and night by the globe, 528

XXVIII. To find where an eclipse of the moon is visible, p. 528
Problems on the celestial globe, 529
I. To place the globe so as to represent the heavens for any evening in any latitude, ib.
II. To find the right ascension and declination of a star, 531
III. Having the right ascension and declination given, to find the star, ib.
IV. To find the latitude and longitude of a given star, ib.
V. } To find on what day a
VI. } given star comes to the meridian at a given hour, ib.
VII. To find the altitude and azimuth of a given star, ib.
VIII. The azimuth, &c. given, to find the altitude, ib.
IX. To find the azimuth and hour of the night, 532
X. Azimuth and latitude given, to find the altitude and day of the month, ib.
XI. Observing two stars to have the same azimuth, to find the hour of the night, ib.
XII. To find the rising, setting, &c. of a star or planet, 533
XIII. To find those stars which never rise, or never set, ib.
XIV. To illustrate the phenomena of the harvest moon, 534
XV. To illustrate the equation of time, ib.

Problems performed by maps, N^o 122
Promontory defined, 53
Ptolemy's work on geography, 21
Ptolemy Philadelphus improves geography, 15
Pythias, voyage of, R. 17
Right sphere, 90
Rivers defined, S. 48
Sataspes, voyage of, 12
Scylax, expedition of, 13
Seas defined, 43
Senex's improvement of the globes, 109
Smeaton's improvement of the globes, 110
Sphere, oblique, 89
right, 90
parallel, 91
armillary, by Ferguson, 112
by Long. 113
invention of, ib.
Strabo's work on geography, 19
Straits defined, 45
Sun, problems respecting, 95
T.
Taprobana, situation of, 28
Time, problems relating to, 67
Tropics explained, 73
Twilight explained, 97
uses of, 98
problems respecting, 99
W.
Wright's improvement of the hour circle of the globes, 66
Z.
Zones, division of the earth into, 76
Zone, torrid, countries in, 77
temperate, places in, 79
frigid, countries in, 81

THAT part of natural history which treats of the internal structure of the earth, as far as we have been able to penetrate below its surface; of the arrangement of the materials of which it is composed, and of the changes which have taken place in these, is called GEOLGY, from γη, the earth, and λογος, a discourse. This science has been called by Werner, GEOGNOSY, and is by him defined to be that part of mineralogy

which, considering minerals as a part of our globe, treats chiefly of their bearings and positions with respect to each other (A). Till of late this department of literature was called physical geography, but at present the terms GEOLOGY and GEOGNOSY are generally adopted; of these we have preferred the former, as being equally expressive and more familiar; and under this head we propose to include every thing that is usually comprehended under what have been called theories of the earth.

GEOLOGY differs from COSMOGNOSY as a part from the

(A) Werner has probably made this trifling change from a desire of novelty; and some of his admiring pupils have attempted to display in very pompous but puerile terms, that it is of great value and importance.

Introduction the whole; the object of the latter is to give an account of the creation of the universe, while the former confines itself to the consideration of the planet which we inhabit.

2. Geology is intimately connected with mineralogy, and may indeed be said to depend on this as its very foundation. Werner, as we have seen, considers Geology as a part of Mineralogy; but we are disposed to concur with Dr Kirwan, who, speaking of mineralogy with respect to its relation to geology, calls it "the alphabet of the huge and mysterious volume of inanimate nature."

Division. Geology may be divided into descriptive and speculative; the former giving a general account of the materials of which the globe is composed, and of their arrangement; while the latter is strictly confined to what may be called a theory of the earth, or an attempt to explain the manner in which the structure and arrangement have been brought about, and the changes that have taken place in the disposition of the component parts of the earth.

3. Importance of the science. The science of geology is of considerable importance in many points of view.

4. to the naturalist; 1. The student of natural history cannot but derive a great fund of profit and advantage from a science, which makes him acquainted with so large a department of nature. Mineral bodies, whether we consider them as individuals of nature, or as collected into those masses which form the strata of the earth, and the mountains that rise above its surface, are peculiarly interesting to the naturalist, as well from the variety of form and beauty of appearance which some of them present, as the useful purposes to which many of them are applied. The other kingdoms of nature delight us with the display of order and design exhibited in their organization, or interest us from the intimate connexion which subsists between many of them and ourselves. These are objects of the beautiful; while the stupendous mountain, the awful volcano, the towering cliff, the gloomy mine, and the majestic cavern, are objects of the grand and the sublime.

5. to the miner; 2. To the miner, and all those who are employed in searching the bowels of the earth for the treasures which they contain, geology, as well as mineralogy, forms an essential qualification. Experience has shown that certain minerals and metals are found more frequently attached to some of the stony materials of the earth, than to others, and that a few of them are only found in particular strata. Examples of this kind will be given presently. We have also learned that the arrangement of the materials in the earth is so far regular and uniform, that when we know the particular materials near which certain metals and minerals are commonly found, and the usual disposition in these places; and when we find in another situation the same materials disposed in a similar manner, we are pretty certain that the metal or mineral of which we are in search is not far distant. We are therefore encouraged to prosecute the search with every probability of success. Those who undertake to direct an investigation of this kind, or to carry on the operations requisite for the obtaining what is sought, would do well to inform themselves beforehand of such facts as are well established respecting the distribution of the materials of the earth, and the substances usually found connected with them.

For want of this necessary information, we often see projectors impose on the credulity, and impoverish the finances, of gentlemen of landed property, who are led to suppose that they possess on some part of their estate a rich vein of metal, seam of coal, &c. the working of which will considerably improve their income.

3. The failure of undertakings of this kind, partly to the land, from the villany of the projector, and partly from the ignorance of his employer, shews the advantages that gentlemen of landed estates would derive from the study of geology. An acquaintance with this science would guard them against the artifices of designing men, and prevent them from embarking in uncertain and expensive projects, the issue of which is too often ruin and disappointment.

4. But the study of geology boasts a still higher advantage. Nothing has more contributed to demonstrate the truth of the divine writings, and to clear up many doubtful passages in them, than the discoveries that have lately been made in the structure and formation of the earth. The original state of the globe is so intimately connected with that which it at present exhibits, that we cannot properly understand the latter without referring to the former; and recent experience has shown that the obscurity in which the philosophical knowledge of this subject was involved, has been highly favourable to those systems of atheism and infidelity which prevailed in the last age. Much of this obscurity is now removed; and the investigations of Whitehurst, Werner, Kirwan, Howard, and some other geologists, by proving that the supposition of a deluge is the only hypothesis on which we can account for the present state of our globe, have contributed as much to the advancement of true religion as of philosophical knowledge.

"So numerous indeed, and so luminous, have been the more modern geological researches, and so obviously connected with the object we have now in view, that since the obfuscation or obliteration of the primitive traditions, strange as it may appear, no period has occurred so favourable to the illustration of the original state of the globe as the present, though so far removed from it. At no period has its surface been traversed in so many different directions, or its shape and extent under its different modifications of earth and water been so nearly ascertained, and the relative density of the whole so accurately determined, its solid constituent parts so exactly distinguished, their mutual relation, both as to position and composition, so clearly traced, or pursued to such considerable depths, as within these last thirty years. Neither have the testimonies that relate to it been ever so critically examined and carefully weighed, nor consequently so well understood, as with-Geol. Essays, in the latter half of the 18th century."

Geological researches seem at first view to be attended with almost insurmountable difficulty. It is evident that the part of the earth which it is in our power to examine, is infinitely small when compared to that which is entirely beyond our reach; and even much of the elevated parts, that appear above the surface, would seem to be so completely cut off from us by inaccessible precipices, and the ice and snow with which the summits

mits of some of them are perpetually covered, that our knowledge of their structure and compositions must for ever remain imperfect. Much of these difficulties, however, is rather apparent than real. It is true that our researches can extend but a very little way below the surface; but so far as our experience has yet taught us, any farther investigation would be rather a matter of curiosity than utility. Those metals and minerals which prove of most service to mankind, are found at no very great depth in the earth, and some of them almost on its surface; and when we have penetrated beyond these, the materials discovered are of a nature so uniform, and of a texture so firm and hard, that it is possible they may extend even to the centre. Again, the investigations of Saussure, De Luc, Dolomieu, and Humboldt, have proved that the most dangerous precipices, and the highest summits of those immense mountainous chains which traverse the earth in so many directions, oppose but feeble barriers to persevering industry and philosophic ardour.

The diversity which occurs in the structure and local arrangement of subterranean substances, seems to throw another difficulty in the way of the geologist; but the farther his researches are extended, the more will this apparent diversity be diminished. The practical skill which some miners possess in many parts of the world, proves that the mazes of this labyrinth are not without a clue; and we may safely conclude, that when our knowledge of the structure of the earth, and the disposition of its materials, shall be still farther extended, the greater part of the obscurities under which the subject is now veiled, will be entirely removed. Multiplied observations of later years have enabled us to form certain general conclusions, and lay down certain general laws, which must materially assist future observers.

In the modern improvements of geology the Germans led the way, and Lehmann may be considered as the father of the science. Eminenty skilled in general physics, practical mining, mineralogy, and chemistry, and fully acquainted with the circumstances attending the relative situation of most mineral bodies in very extensive tracts of different countries which he examined, he was enabled to deduce, from a long series of observations, some general conclusions, which have, with some exceptions, been since verified in every part of the world.

Lehmann was followed in his own country by Bergman, Ferber, Gmelin, Cronstedt, Born, and Werner; in Italy, by Arduini and Tulas; in Switzerland, by Saussure and De Luc; in Russia, by Pallas; in France, by Delametherie, Saint Fond, Dolomieu, and Lavoisier; and in Britain, by Hutton and Kirwan, names which must ever be held in the highest estimation by the cultivators of this part of natural history.

Before entering on the study of geology, it is necessary to acquire a competent knowledge of chemistry, and a pretty extensive acquaintance with mineralogy, as these sciences form an essential introduction to the more general researches respecting the structure of the earth. The former supplies the means of ascertaining the nature of the substances met with; and the latter must be well understood, before we can arrange these substances under their proper heads, and before we

can comprehend the terms employed by geological writers. Introduction.

The study of this science, like that of some other parts of natural history, particularly botany, can be prosecuted with but little advantage in the closet. The student must examine the declivities of hills, the beds of rivers, the interior of caverns and of mines, the recesses of the ravine, and the utmost summits of the mountain, before he can obtain that degree of knowledge which is necessary to constitute a skilful and philosophic geologist. While making these personal observations, he should study the works of the best writers, and compare the facts related and described by them, with those which he himself has observed. The writings on this subject may be divided into two principal classes, one comprehending those works which contain a systematic account of the whole, or some part of the subject; such as Bergman's Physical Geography, the Geological Essays of Kirwan, the Theorie de la Terre of Delametherie, the writings of Werner, &c.; and the second comprising those works which treat of the geology of particular countries in the familiar style of travels; as Born's Travels in Hungary, Ferber's Travels through Italy, Saussure's Voyage dans les Alpes, Pallas's Travels, Jar's Voyages Metallurgiques, Saint Fond's Travels in England and Scotland, &c. After having acquired a knowledge of the principles and general facts of the science from the former, the student will, by means of the latter, increase his knowledge in the most familiar and agreeable way.

In the sketch of geology which we are to give in the following article, we shall consider the subject under three general heads, which will be the subject of as many chapters.

In the first chapter we shall describe the arrangement and distribution of the materials of which the earth is composed. Here, after giving some general notion of that arrangement, we shall consider each of the principal materials under a separate section, in which we shall first lay down those general marks by which each is distinguished, describe its general arrangement, and mention the places, especially in Britain, where the substance is found in greatest abundance, and those metallic or mineral bodies which are commonly found in connection with it. After having briefly considered each substance, we shall bring the more general distribution of them under one view, still directing our attention to the arrangement of these materials in the British islands.

In the second chapter we shall give a brief outline of the most remarkable theories that have been framed in modern times, to account for the distribution of mineral bodies, and the manner in which we find them now arranged. In this chapter we shall dwell more particularly on the two rival theories which at present divide the geological world, and shall enumerate some of the objections which have been made to each.

In the third chapter we shall give some account of the derangement of the substances that compose our globe, so far as it has originated from known causes; and this will lead us to the consideration of EARTHQUAKES and VOLCANOS.

CHAP. I. Of the Arrangement and Distribution of the Materials of which the Earth is Composed.

THE materials of which the general mass of the earth is composed, are variously distributed in different parts. In some places they form irregular masses or blocks, either buried below the surface, or elevated to a greater or less height above it. In most places, however, the materials are arranged in a more regular manner; those of the same kind being collected into extensive masses, lying in layers or strata, above or below a similar mass of another kind, or these alternate with each other to a considerable depth. These strata are sometimes found arranged in a direction parallel to the horizon; at others they are vertical, or perpendicular to the horizon, appearing as if the horizontal strata had been lifted up, and laid upon their edges. More commonly the strata are arranged in a direction inclining to the horizon, when they are said to dip.

The uppermost stratum is in most places covered to a certain depth with mould that has evidently been formed from the decomposition of organized substances. In many parts of the earth this mould extends to a very considerable depth, and constitutes the soil; in other places it is barely sufficient to form a coating to the strata, and in others it is entirely wanting.

A good instance of horizontal strata occurs about two miles to the east of Balleycastle in the north of Ireland, of which we shall speak more particularly by and by. One of the most curious examples of vertical strata in Britain is found in the small island of Caldey, on the coast of Pembrokeshire, where the strata of which the whole island is composed are placed in such a manner, that their edges are all exposed to view, and they may be successively examined from the one end of the island to the other. It is seldom that an opportunity offers of examining the arrangement of strata so easily as is afforded in this small island. In most cases it is necessary to penetrate to great depths before we can acquire an imperfect knowledge of the stratification of the earth; and in no instance have we yet proceeded a mile below the surface. In Caldey island, however, the strata may be examined to the extent of more than a mile, beginning at what may be supposed the uppermost stratum, which is not more than a foot thick, to that which may be called the lowest, at the opposite end of the island, being a mass of red stone of more than a mile in depth.

Sometimes the strata are continued in a regular arrangement of the arrangement, preserving the same inclination to a very considerable extent; but more commonly they appear in some parts separated, as if they had been broken asunder. These separations are usually in a perpendicular direction, and the cavities are found filled with various heterogeneous matters. Sometimes these are chiefly composed of fragments of the adjacent strata, but for the most part they consist of mineral or metallic substances of a different nature.

When these fissures are filled up with broken fragments, or rubble, as it is called, it very commonly happens that they become the beds of brooks or rivers. Thus the river Derwent runs for a considerable extent in Derbyshire over a fissure of this kind. When the fissure is filled up with a solid stony matter, this forms

what in Scotland is called a dyke. If a mass of mineral or metallic matters fill the fissure, or be infiltrated between the strata, it forms what is called a vein, and these veins sometimes branch between the strata in various directions.

When a fracture has taken place in the stratified mass, one part of the mass sometimes preserves the same position as it had before, or still forms a continued line with the other parts of the mass, or is parallel to it; but more frequently one part is thrown out of its original position, and becomes more inclined to the horizon than before. Sometimes one side of the mass is more depressed than the other, as is commonly seen in many of the strata in Derbyshire; at others the two parts of the mass are so disturbed as to incline towards each other, as if they had been broken upwards. When the edges of the strata on each side of the fissure are thus divided and disarranged, they are said by the miners to trap.

The chasms thus formed are sometimes of considerable width. Some are found in Cornwall nearly 20 feet across, and almost full of metallic and other mineral substances. It not unfrequently happens, that these fissures are empty, containing nothing but water in the bottom. A celebrated chasm of this kind is shewn at the Peak in Derbyshire; and if a stone be thrown in, it is heard to strike from side to side for a considerable time, till at length it seems lost in subterranean water.

If the country in which the strata lie runs in a wavering direction of hill and dale, the strata usually preserve the same wavering direction, keeping pretty nearly parallel to each other. A curious example of this kind has been described by Gerhard, as occurring in the district of Mansfield in Germany. See fig. 1. In those places where some remarkable dislocation of the strata has not taken place, their distribution is in general extremely regular, certain materials lying above or below certain others in an uniform manner. The observations of later geologists have discovered pretty nearly the arrangement that takes place in most countries; and we shall presently give some examples of the stratification of several parts of Europe. Before we attempt this, however, we must mention some circumstances in which the materials composing the strata differ from each other.

The general observation of all modern geologists proves, that all these materials may be distributed under the two general classes; one consisting of those substances which are found more or less connected with the remains of organized bodies, as the bones, teeth, and shells of animals, the trunks of trees, and other parts of vegetable bodies; and the other comprehending those in the substance of which these organic remains are never found. As it is now generally believed that the latter of these are of a formation prior to the former, we shall here adopt the general division of them into primary and secondary. We might go still farther in this division, by arranging them under more heads; one, for example, containing those in which organic remains are sparingly found, and others containing those substances which are found only in particular places; but as the first of these involves in it a particular theory which we shall notice fully hereafter, and the others allude to facts which will be mentioned when treating of the separate materials, we shall not here extend our division

division beyond the distribution of the materials into primary and secondary.

In the following short detail, many terms will occur which can be understood only by the mineralogist. They will be fully explained under the article MINERALOGY. The names which we shall give to the substances described will be such as have been most generally adopted in this country; but to prevent ambiguity, we shall, where it seems to be necessary, add the synonymous names that occur in the best geological writings.

A. Primitive Compounds.

SECT. I. Of Granite.

THE name granite has long been applied to all stones which are composed of an aggregate of quartz, feldspar, and mica, distributed in such a manner as that each of them appear in a separate state; but as this definition has been considered as too loose, and comprehending too many varieties, the name is at present restricted to that kind of granitic stone in which the quartz, feldspar, and mica, are found in grains or crystals. Of the three substances, the feldspar is generally the most abundant, and the mica the least so.

Granite is found in the lowest and the highest situations of the earth that have yet been examined. It forms the basis of all the other strata; and though these are sometimes found below it, this situation seems to have been the consequence of some accident, by which the inferior substances were thrown below the granite. Many mountains seem almost entirely composed of granite, as Geforn one of the Rhætian Alps; and there is a high hill of white granite about six miles to the west of Strontian in Scotland. Sometimes large masses of granite are found in a detached situation at some distance from the mountains to which they appear to belong; and these masses seem in some instances to have been broken off, and rolled down the mountain, and in others to have been carried away by irresistible torrents, or dislodged by earthquakes. On the summits of the mountains near Port Sonnachin in Scotland, are found large quantities of detached pieces of granite, some of them of amazing size *.

Granite is most commonly found in vast blocks, separated from each other by rifts or chasms, irregularly disposed. This is the case in most mountains, especially in those which have high, pointed spires. The structure of these blocks is pretty uniform, there occurring seldom more than two varieties, one called porphyritic granite, in which the basis is of a fine grain, containing large crystals of feldspar. Of this variety many instances occur in the north of Scotland, and near Carlisbad in Bohemia. The other principal variety is that in which the granite is found in distinct globular concretions, composed of concentric lamellæ. This variety was observed by Mr Jameson, on the road between Dresden and Bautzen; and Mr Barrand, in his description of the Cape of Good Hope, mentions several globular concretions of immense size. The isle of Arran

in Scotland also affords instances of the same variety. It is also found in Corsica, and is often called Corsica granite.

It has been doubted by some geologists, whether the true granite is ever found stratified; but numerous instances of its stratification have been lately adduced, that leave no room to doubt that this is sometimes the case. Pallas takes notice of some stratified granite on the banks of the river Berda, where what he considered as perfect primitive granite, compactly crystallized, is disposed in layers of various degrees of thickness, some not exceeding one-eighth of an inch, and bounded both above and below by blocks of solid granite †. Again, on the banks of the Gromoklea, he observed similar layers of granite running in a direction from north to south, each bed being from one span to three feet six inches in breadth, and consisting of the most perfect primitive granite, which he considers as a continuation of that mineral tract which produces the cataclasts of the Dnieper ‡. Mr Playfair mentions an example of stratified granite which he saw in Chorley forest in Leicestershire, where real granite is disposed in beds on the eastern border of the forest, especially near Mount Sorrel. Another instance of real granite disposed in regular beds, is also mentioned by Mr Playfair as occurring near the village of Priestlaw in Berwickshire ||. Mr Jameson observed the Riefengebirge, which separates Silesia from Bohemia, to be for 150 miles composed of granite disposed in horizontal strata, and he observed a similar stratification in Saxony and Lusatia ¶.

Granite constitutes the base of most of the British mountains, but is more commonly met with in the north and western parts of the island. There is a considerable mass of granite which runs longitudinally through Cornwall, from Dartmore to the Land's End *. Considerable masses are found in Scotland, but their extent has not been accurately ascertained. According to Mr Playfair, there is no mass of any magnitude in the southern parts, except that of Galloway, which occurs in two pretty large insulated tracts. Mr Playfair thinks that Dr Hutton greatly underrated the quantity of granite in Scotland, which, especially in the north, he considers as extending over a large district. If we suppose a line to be drawn from a few miles south of Aberdeen, to a few miles south of Fort William, it will, according to Mr Playfair, mark out the central chain of the Grampians, along which line there are many granite mountains, and large tracts in which granite is the prevailing rock †.

It is remarkable that in the mountainous regions of Peru, especially in the environs of the volcanoes, no granite is found, except in very low situations, at the bottom of valleys ‡.

Several varieties of granite are subject to decay, from the decomposition of the feldspar which they contain. This circumstance will probably explain a curious fact. It is found that the granite existing in the interior of mountains is much softer than that near the surface, probably from the decay of the feldspar in the latter, while it remains in its original state in the former (B).

Granite

(B) The decomposition of granite appears to go through several stages, from the solid rock to the loose sand. These

Arrangement, &c. of the Materials of the Earth. Granite is by no means abundant in metallic and the richer mineral substances; it, however, contains a considerable variety, some of which have as yet been found in no other substance, especially molybdena. Iron ores are very commonly found in granite, especially the compact brown iron stone. It seems to be owing to the presence of iron that granite assumes that fine reddish colour with which we sometimes see it tinged. One of the most remarkable instances of this kind is afforded by the rocks to the south-east of the valley of Chamouni, at the foot of the Alps. These rocks, from their red appearance, are called Les Aiguilles Rouges, or the red needles. These rocks were mentioned by Saussure, but he had not ascertained their composition. This has since been done by M. Berger, who found them to be composed of granite, with a considerable quantity of oxide of iron*. Bismuth, cobalt, blende, galena (an ore of lead), and several ores of copper, are also sometimes met with; but the metal most frequently found in granite is tin, especially in the great mining field in Cornwall.

SECT. II. Gneiss.

GNEISS, by some writers called kneist, is not unfrequently confounded with granite, from which it differs rather in the arrangement than in the nature of its component parts. These in gneiss are arranged in a schistose or slaty form, whereas in granite, they are in distinct grains or crystals, the layers being generally in the direction of the mica. It sometimes is intimately incorporated with masses of granite, but, in most instances, it reposes on the granite, being generally the second layer. In descending into the valley of Chamouni, Saussure observed a fine bed of true granite incorporated with a rock of gneiss, which was arranged in very fine leaves†. Sometimes the gneiss lies entirely below the granite; but this is uncommon. More generally there is found a vertical mass of granite, with strata of gneiss on each side of it. Very frequently granite and gneiss alternate with each other.

Sometimes whole mountains are composed of gneiss. Thus, Ben Lomond scarcely contains any other substance, and the Schaw, which is the most northern point of the northernmost of the Shetland islands, is entirely gneiss. Mountains of this kind are, in general, neither so high nor so steep as those of granite, though Mount Rosa in Italy, and a few others, must be excepted. The summits of these mountains are also generally more rounded than those of granite mountains. The bases of all the Shetland islands seem chiefly composed of gneiss, and the middle part of the Pyrenees is almost wholly formed of this and granite.

It is curious that where gneiss is contiguous to gra-

nite, its quartz and feldspar are more apparent, and the mica less so; while, where it is more distant from granite, the contrary happens‡. Several metallic ores are found in gneiss, particularly those of iron, as the magnetic iron stone, and martial pyrites; lead ores, tin ores, blende, cobalt, copper, and arsenical pyrites, and not unfrequently silver ores.

SECT. III. Micaceous Schist.

This is otherwise called schistose mica, and mica slate. It is also composed of the same materials with granite and gneiss, except that it contains little or no feldspar; the quartz and mica being arranged in layers as in gneiss.

This substance also is very abundant in most rocks and mountains. It generally composes the third layer or stratum, being immediately above or without the gneiss. It not uncommonly appears to be the only substance composing the hill or mountain, from the gneiss and granite being probably so completely covered as to be out of sight.

Micaceous schist composes the rocks that are found immediately to the north of Dunkeld in Scotland, and it is here penetrated in every direction by veins of quartz. The southern shores of Loch Tay, the mountains of Glen Lochy, the vale of Tumel between Loch Tumel and Loch Rannoch, contain much of the same substance; and the lower part of Glen Tilt is chiefly composed of it. In the western Highlands towards Ben Lomond, micaceous schist also abounds, and some of it is found in the north of Argyleshire. The Shetland islands are mostly composed of micaceous schist, in thick layers above the gneiss, with a few masses of granite interpersed.

It not unfrequently happens that a bed of micaceous schist is intersected by veins of granite. Mr Jameson observed an example of this in Glen Drummond in Ba-
*Min. of the Isles, vol. ii. p. 173.

The metallic ores found in micaceous schist, are chiefly those of iron, copper, tin, lead, cobalt, and antimony.

SECT. IV. Quartz.

QUARTZ is not unfrequently found distinct from feldspar and mica, and sometimes whole mountains are found composed of it. In particular, the mountain of Kultuc, at the south-east end of the lake of Baikal, among the Altaishian mountains, which is 4800 feet long, 350 high, and above 4000 broad, consists entirely of milk-white quartz; and the mountain of Flinzberg

These are thus marked by Mr Jameson. In its beginning disintegration it splits into masses, having a greater or less tendency to the quadrangular form; but these masses have still a degree of connexion amongst themselves, as is the case upon the mountain top. The next step is the enlargement of the fissures, by which the masses are loosened from their connexion, and tumble down from their elevated situations, upon the summits of the neighbouring mountains, or are hurried with impetuous velocity down the mountain side, covering the bottom of the glens with their stupendous ruins. Lastly, These detached masses, by the action of the weather, are completely disintegrated, forming a loose sand, which is left upon the tops or sides of the mountains, or is carried in great quantities to the sea shore by the torrents. Jameson's Mineralogy of the Scottish Isles, vol. i. p. 82.

berg in Luface, is almost wholly composed of it. There is also an extensive ridge of quartz, some miles long, in Bavaria, and Monnet mentions a rock of it 60 feet high. Mountains of it are also found in Thuringia, Silesia, and Saxony. It sometimes forms layers between gneiss and micaceous schistus. A considerable stratum of this kind, consisting of granular quartz, is found between granite and micaceous schistus in the island of Idav, see fig. 4. b. It is often found forming spires on the tops of mountains, and appearing like snow.

Quartz is found in several parts of Britain; but there is very little of it in the southern part of the island. Williams found it very common in the Highlands of Scotland, where he has seen it regularly stratified, with other regular strata immediately above and below it; and sometimes composing high mountains entirely of its own strata. These strata are sometimes moderately solid; but often are naturally broken into small irregular masses, with sharp angles, and of a uniformly fine granulated texture, resembling the finest loaf sugar.

There are large and high mountains of this stone in the shires of Ross and Inverness; and in a clear day these appear at a distance as white as snow, being quite bare of vegetation, except a little dry heath around the base of the hill.

The mountain of Swetlaia Gera, one of the Uralian chain, consists of round grains of quartz, white and transparent, and of the size of a pea, united without any cement.

No metals are found in quartz, though it sometimes contains petroleum.

SECT. V. Argillaceous Schistus.

This stone, which is otherwise called clay slate, is the shonchieffer of Werner, and the argillite of Kirwan. It is of the same nature with gneiss and micaceous schistus; but in this the stratification is still more complete, and all traces of crystallized granite entirely disappear. Doubts have arisen whether this stone is primitive; but these are now cleared up, as it is frequently found alternating with gneiss and micaceous schistus, especially in Saxony, and with other primitive strata. It sometimes happens, too, that both gneiss and granite rest upon it.

There are two varieties of this stone, one hard, and the other soft; but the hard often graduates into the softer.

Sometimes this stone is found forming whole mountains; but more commonly it enters into them only partially. In some, however, there are entire strata of it, as at Zillerthal, in the Tyrol. The famous mountains

of Potofi consist entirely of argillaceous schistus, and Sauffure found it on the summit of Mont Blanc.

In Britain it is not very common; but is sometimes found on the higher parts of mountains. Thus it forms the summit of Skiddaw in Cumberland.

Argillaceous schistus, especially the softer variety, is remarkably rich in metals. We have said that it forms the greater part of Potofi, one of the richest silver mines. The ores of copper and lead, sulphur, pyrites, blende, and calamine, are also found in it. The great belly of copper ore in the Parrys mountain in Anglesea, is found below this substance. It also sometimes contains antimonial and mercurial ores.

SECT. VI. Jasper.

It was supposed, by the earlier mineralogists of the last century, that jasper was only pure quartz, so much penetrated by a colouring metallic oxide as entirely to deprive it of its transparency; but Sauffure and Dolomieu, with their usual accuracy, discovered that it consists of flint, and not of pure quartz, having in combination a quantity of argillaceous matter, more or less mixed with oxide of iron.

Primitive jasper is always opaque. It is commonly found imbedded in other stony matters. In colour it varies from red to green, and frequently consists of alternate stripes of red and green, sometimes perfectly distinct, at others running together. There is a beautiful variety figured by Patrim, in which a dark-red ground is crossed in every direction with curved white lines, leaving here and there circular spaces of red surrounded with white, forming eyes.

Striped jasper is sometimes so abundant, as to be the chief material of some mountains, in which it is mixed with broken fragments of granite and other primary compounds (c). Mountains of red and green jasper also occur. Generally, however, it appears in strata, interposed between layers of micaceous schistus, or alternating, and sometimes mixed with compact red iron stone. It is found in the south of France, reposing on granite; and in the Altaischen mountains, it sometimes lies below argillaceous schistus, but has there never been found in contact with granite. A coarse kind of jasper is sometimes found in the hills near Edinburgh; and some fine specimens are met with in the northern mountains.

SECT. VII. Hornstone.

This stone is considered by Dr Kirwan as the same with petrosilex, but Patrim and some others distinguish them.

(c) There is often found interposed between the strata of rocks, or sometimes above the upper stratum, a bed of fragments that have been broken off from the principal strata. When these fragments chiefly consist of limestone and calcareous compounds, whether they be of an angular form, or consist of rounded pebbles, they are generally called by the name of breccia; but when the fragments are of a siliceous or quartz nature, especially if they are agglutinated together, so as to form a solid mass, they have usually been called puddingstone. From the uncertain manner in which these terms were employed, much confusion arose, till Romé de l'Isle, and other later naturalists, have given the name of breccia to every stony mass that is composed of angular fragments, of whatever nature they be; and they call by the name of puddingstone every agglutinated mass that is composed of round pebbles, whether they be calcareous, quartzose, or of any other nature. These compounds will be spoken of presently in a separate section.

Arrangement, &c. of the Materials of the Earth. According to Patrim, hornstone is a compound primitive rock, composed of the same elements with granite, in which schorl is very abundant, communicating to the stone a dull, gray, or sometimes blackish, colour, and containing a pretty large quantity of the argillaceous matter of mica. Petroflex, according to him, is purer than hornstone, and commonly of a grayish or greenish colour, semitransparent, and very hard, so as to give fire with steel. They are often found united, and sometimes form entire mountains, containing fragments of feldspar interspersed. They are commonly found in large thick masses or blocks, though they are sometimes stratified like the schistose stones. Dolomieu is mistaken, when he asserts that petroflex is only found in primitive mountains, as it will appear hereafter, that it is sometimes a secondary compound. At Tuhumas, in the isle of Rona, Mr Jameson found a mass of rock chiefly composed of hornstone and quartz, from 12 to 15 feet wide, and of considerable length, lying between two beds of gneiss.

³⁸ Pitchstone described. THE Germans have given the name of pitchstone, or pechstein, to a stony matter, which is found in large masses of an irregular form, and of different colours, as yellow, brown, red, green, &c. having sometimes the appearance of rosin, and sometimes that of an enamel, or of glass imperfectly transparent. It is never crystallized.

³⁹ Where found. It is found, either in large masses, or in veins. At Misina, it is found forming entire mountains; and in other countries there are mountains containing strata of pitchstone, sometimes alternating with granite, at others with porphyry. Mr Jameson describes a large vein of it of a green colour, several feet wide, traversing a mass of red argillaceous sandstone, at Tormore in the isle of Arran. This vein is extremely curious, and contains strata of different substances deposited in the same fissure*. Another curious vein of pitchstone is described by him as traversing a basaltic rock, together with a vein of hornstone, in the island of Eigg†. Mr Jameson considers this as the first example of pitchstone traversing basalt, discovered in Europe, though similar appearances have been found on the top of the peak of Teneriffe.

Pitchstone is only considered as a primitive rock, when it is nearly allied to porphyry.

⁴⁰ Hornblende slate. HORNBLENDE is sometimes found existing separately from the compounds in which it usually occurs, as is the case in Siberia, where there are mountains of black hornblende. It is often found mixed with quartz, mica, feldspar, or schorl, of a greenish or black colour. More commonly, however, it occurs in immense strata, sometimes in layers of gneiss, argillaceous schistus, or primitive limestone. A stratum of it above primitive limestone has been found at Miltiz. It is sometimes seen below granite, or granite is even found imbedded in it. A rock of hornblende, reposing on granite, has been seen by Mr Jameson in the isle of Arran; and on the side of Loch Fine he found it alternating with strata of micaceous schistus‡.

The principal metallic substances found in hornblende slate, are native sulphuret of iron and copper ore.

SERPENTINE is a stone of a similar nature with respect to its ingredients with those we have been describing. It takes its name from its appearance, being generally of a greenish ground, marked with white, yellow, brown, or reddish spots, so as to bear some resemblance to the skin of a snake. Its green colour is owing to a quantity of slightly oxidated iron which it contains. It is usually opaque; but sometimes parts of it are semitransparent, and though not very hard, is capable of receiving a good polish.

Serpentine is by no means uncommon, and is often found in layers alternating with primitive limestone, or below gneiss. The hill of Zobtenbeg in Lower Silesia, consists almost entirely of serpentine, disposed in nearly vertical strata, with a little hornblende interspersed. Whole mountains of green serpentine are also found in Siberia, and near Genoa, where it is called gabbro or pulverenza. It is also found near the White sea, and the mountain of Regelberg in Germany is chiefly composed of it. Rocks of it are found near the Lizard Point, on the coast of Cornwall; and hills of it occur in some of the Shetland islands.

Metals are seldom found in serpentine, except a magnetic ore of iron, which not unfrequently forms a part of the serpentine rocks, imparting to them its magnetic power. Veins of copper sometimes traverse it.

PORPHYRY generally consists of the same materials as granite, but in different proportions, and having altogether a different appearance; for instead of being crystallized as in granite, we find in the true porphyries an uniform compact mass, in which are disseminated small crystals of feldspar, and sometimes of schorl. There are, however, many varieties forming shades between granite and true porphyry, several of which are described by mineralogists.

Porphyry is very abundant in many situations, forming a considerable part of hills, and even mountains. It sometimes alternates with gneiss, and has been found below it. Gneiss has also been found in the midst of porphyry. It sometimes occurs in the midst of micaceous schistus, and sometimes forms an external covering to other primitive strata. Whole mountains of porphyry, arranged in immense strata, sometimes repose on a base of granite or gneiss. This stone is found in the greatest abundance in several places between the tropics, especially in South America, where it is sometimes met with at immense heights*.

Porphyry is very common in most parts of Scotland, and, in particular, forms a considerable stratum at the top of the Calton hill at Edinburgh, being in some places 12 or 15 yards thick, covering a bed of breccia.

Porphyry is found in considerable quantity between Newcastle and Wooler, and blocks of it of considerable size may be every where seen scattered about in the fields. The feldspar of these porphyries being less durable than the rest of the stone, is partly destroyed in some.

* Jameson's Mineral. of the Isles, vol. i. p. 102. † Id. vol. ii. p. 44.

‡ Min. of the Isles, vol. i. p. 74.

Arrangement, &c. of the Materials of the Earth. some blocks, and appears corroded in others; from which circumstance the porphyries are so porous, as to appear as if they had been burnt. Porphyries of a similar appearance are found in the mountain of Esterle in Provence, on the road from Frejus to Antibes.*

* Saint-Just's Travels, vol. i. p. 164. There is a variety of porphyry mentioned by Charpentier, a great part of whose composition is indurated clay, and nodules of clay of different colours are found in its substance. Specimens of a similar nature occur in the western islands of Scotland. There is also a species of porphyry nearly allied to hornstone.

45 Metals found in it. The two varieties last mentioned are rich in metallic ores; in the former there being formed ores of silver, copper, iron, lead, and antimony; and, in the latter, sparry iron ore, native sulphuret of iron, galena, black blende, and ores of bismuth.

47 Schilfole porphyry. A stone of a porphyritic nature is described by Werner under the name of schilfole porphyry, and is considered by Kirwan as the same with the horn slate of Charpentier. It is found among the primitive rocks of Altai, and on the borders of the lake of Baikal, in which latter place it is mixed with granite and hornblende. It is also found in Siberia, and in Bohemia. Saussure found it near Pfaffenprung, intercepted between strata of gneiss.

48 Pudding-stone and breccia. SECT. XII. Pudding-stone and Breccia.

49 Examples of breccia. THE distinction between these two stony matters was mentioned in note c: they are both sufficiently common, consisting of different materials. The breccia usually lies in bodies, almost at the top of the other primitive strata, with some of which it sometimes alternates. Stratified breccias, consisting of fragments of flints and jasper, cemented by hardened clay, are frequently found in Siberia, and sometimes alternate strata of breccia, porphyry, jasper, and other primary compounds, compose a considerable part of mountains. Some mountains in the north of Scotland contain masses of breccia, composed of fragments of red granite, micaceous schistus, and quartz, in a base of sandstone. Mount Scuraben contains strata of this kind, surmounted by a rock of white quartz. Similar appearances take place at Cromarty, at Murray frith, and two or three miles to the south of Aberdeen; but in many of these instances the breccia must be considered as secondary. Much of the northern coast of Scotland abounds with breccia.

50 Of pudding-stone. Pudding-stone is also extremely common. A mountain of it is found in Siberia, near the rivulet of Tulat, being composed of fragments of jasper, chalcidony, aigue marine, and cornelian, cemented by a quartzose matter. Immense heaps, and even a mountain of pudding-stone, are found at Meisenheim, in the palatinate. Pudding-stone is found in considerable abundance in passing from Loch Ness to Oban, in Scotland, and between Inverness and Dunoll. Large detached rocks of pudding-stone were seen by Pallas in the village of Temirdiki, in the Crimea. Some of these masses are seven or eight fathoms long, lying one above another.*

* Pallas's Trav. in Crimea, vol. ii. p. 197. SECT. XIII. Sienite.

51 Sienite. THIS name has been introduced by Werner, to de-

note a primary rock, essentially composed of grains of feldspar and hornblende, intimately blended together, in which the hornblende is generally most predominant. He first called it greenstone, but afterwards gave it the name of sienite, as he supposed it similar to a stone described by Pliny, as found at Syene in Upper Egypt, where it was dug in great quantities, and from thence carried to Rome, for the purpose of building public edifices.

Sienite sometimes contains a few grains of quartz and mica; but these seem to be accidental, and are always in very small quantity. This stone is not commonly stratified.

Sienite usually overlays most of the other primary rocks, and has often a bed of breccia interposed between it and the inferior strata. It is very commonly found reposing on porphyry.

52 It is found in Saxony, in the environs of Dresden, at Meissen in Thuringia; in Hungary, and in general in almost all primitive chains of mountains, especially in the Alps. It is doubtless the same which Saussure found in the summit of Mont Blanc, and which he calls granitelle.

53 Metallic veins are not unfrequently found in sienite. At Scharffenberg, veins of silver and lead are found in it; and it is said, that the veins of Aronian in Argyle-shire run in a similar rock.

54 It was long doubted whether limestone was ever to be found unmixed with organic remains, or primitive limestone; but the observations of late mineralogists and geologists have fully proved, that primitive limestone exists in considerable quantity. This stone is of a granular structure, and of a whitish gray colour, though frequently of a dark iron gray, or reddish brown. It is sometimes scaly or lamellar; at others nearly compact, and is now and then found to have a splintery fracture. It is generally unmixed with other primary compounds; but sometimes particles of mica, quartz, hornblende, &c. occur in it.

55 This stone is always found alternating with the primary strata, especially with gneiss, micaceous, and argil-laceous schistus. It sometimes forms whole mountains, as in Styria, Carinthia, and Carniola, in Switzerland and in the Pyrenees, being often found seven or eight thousand feet high. Three mountains in Switzerland, all exceeding 10,000 feet in height, are chiefly composed of it. In these situations it commonly forms immense blocks, without any regular dip or direction; but it is sometimes stratified, as at Altenberg near the lake of Neuenberg. It is sometimes interposed between sienite and hornblende slate. One of the most singular mountains of granular limestone is that of Filabres in Spain, consisting of a block of white marble three miles in circumference, and 2000 feet high, without any mixture of other earths or stones, and with scarcely any fissure.

A considerable part of Mont Perdu in the Pyrenees is composed of alternate vertical bands of granite, porphyry, limestone, hornblende, and petroflex.

Granular limestone is found in various parts of Britain, especially in the north of Scotland. One of the most remarkable examples of it occurs in the island of May

Arrangement, &c. of the Materials of the Earth. ⁵⁶ Metals in it.

Island; the central part of which is formed of a compact bed of it of considerable extent. See fig. 4. d. It also occurs in some other of the Western isles. Primitive limestone often contains veins of metallic ore, especially those of galena, magnetic iron ore, blende, and pyrites.

⁵⁷ Primitive trap described.

TRAP is a name that was long ago given by the Swedish mineralogists, to distinguish certain stones that are of a compact texture, and a dark colour, composing part of several mountains. The word originally signifies a staircase, and was given to mountains containing this stone, because their strata retire one behind the other like the steps of a staircase. But as many rocks of a very different kind, both in their nature and formation, have received the common name of trap, considerable confusion arose among mineralogists, with respect to what particular stones should receive this appellation. Most of the French mineralogists, as Saussure, Dolomieu and Saintfond make trap to signify a primitive rock, but they do not always mean the same rock. Other mineralogists, especially the Germans, understand by the name of trap, certain secondary rocks, and especially what are commonly called basalts.

Werner comprehends under the name of trap, several series of rocks, which are principally characterised by their containing hornblende, which is found almost pure in those which he considers as the most ancient, or what generally lie the lowest; and it degenerates gradually in the succeeding strata into a kind of blackish, ferruginous, hardened clay. He distinguishes three series or formations of traps; primitive traps, transition or intermediate traps, and stratiform or floetz traps. We shall here consider the first of these.

Primitive trap is almost wholly composed of hornblende, though it is sometimes mixed with feldspar, or more rarely with mica and some other substances. Under this general description Werner comprehends four stony substances; hornblende and hornblende slate, which we have already noticed in Section IX. primitive greenstone, and schistose greenstone.

Primitive greenstone is a mixture of hornblende and feldspar; under this there are several varieties, according as its texture is more or less granular, or compact. 1. Common greenstone, in which the hornblende and feldspar are intimately blended, is granular, and bears considerable resemblance to sienite, in which the hornblende is predominant. 2. A second variety has smaller grains, in which are imbedded crystals of feldspar, being of a structure between the granular and porphyritic. 3. A third variety has the grains of hornblende and feldspar extremely small, so as to be scarcely distinguishable. This stone loses its granular appearance, and becomes entirely porphyritic. 4. Lastly, when the mass becomes quite homogeneous, and of a complete green colour, it forms what was once called green porphyry, and constitutes the fourth variety *.

Schistose greenstone is composed of compact feldspar, hornblende, and a little mica, of which the hornblende and feldspar are nearly in equal quantity, and it now and then contains a little quartz. Its structure is schistose.

We have been thus particular in describing what

Werner understands by primitive trap, as whatever may be thought of his theoretical opinions, his talent for mineralogical distinctions and characters cannot be called in question.

Dr Kirwan has given a long section on the distinguishing characters of trap, and its relation to basalt, &c. in his Geological Essays. He thinks that there might be formed a natural series of stones of a trap nature, taking in not only the composition but also the texture, grain, and specific gravity, as something of this kind has been conceived and done by Werner.

Primitive trap is often found in vast strata in the middle of gneiss, and veins of it running through gneiss, have been found in Knobsdorf in Silesia, and in Bohemia. It is also sometimes found in granite, and it is found passing through granite and micaceous schistus in the Western isles of Scotland. Saintfond found it alternating with granite, near St Malo; and Charpentier, with gneiss. It sometimes forms entire mountains, as in the territory of Deux Ponts; and in Norway it is found reposing on granite. It sometimes alternates with argillaceous schistus, as at Leidenburgh.

Primitive trap frequently contains metals, especially the ores of iron and copper.

THIS stone is composed of quartz, schorl, topaz, and lithomarga (a kind of hardened clay), the three former substances constituting small layers or plates alternating with each other. It sometimes contains cavities or geodes, lined on the inside with crystals of quartz and topazes. The texture of this stone is between the schistose and the granular; that is, it is composed of plates or laminae; but these laminae are of a granular structure.

Topaz rock is very rare. It forms part of a mountain near Averbach, in the metallic mountains of Saxony; but no metallic matter has hitherto been discovered in it.

SILICEOUS schistus, or flinty slate, is the kieselschiefer of Werner; but there seems some dispute between his disciples, whether it be a primitive or a secondary rock; on which account we have placed it last in the former series. Brochant does the same; but Mr Jameson, in his sketch of the Wernerian geognosy, places it among the transition formations, or those which immediately succeed the primitive. It is thus described by Mr Jameson. Its colour is bluish gray; it is internally dull; its fracture in the great is imperfectly flat; in the small, large splintery, passing into flat conchoidal; its fragments are indeterminately angular, and pretty sharp edged; it is strongly translucent on the edges; it is Dunfriess, hard and brittle, difficultly frangible, and not particularly heavy *.

An entire mountain formed of this stone is found in Lusatia, in which there are no petrifications. It is also found in the Alps, interposed between gneiss and hornstone. Schlendgenberg, a mountain in Saxony, is for the most part composed of it, mixed with hornblende and feldspar. Kirwan considers it as the same substance.

* Brochant. Mineral. tom. II. p. 582.

Arrangement, &c. of the Materials of the Earth. flance which Saussure calls paléopétite, which is commonly considered as petroflex.

Flinty slate is described by Mr Jameson as among the mineral substances found in Dumfriesshire. He particularly notices an immense rocky mass of it at the entrance of the valley at Leadhills, by which the metallic veins are completely interrupted *.

No metals have been found in it.

B. Secondary Compounds.

THE substances which we are now to notice are distinguished from those which we have been describing, in containing more or less the remains of organized beings. As the inferior strata of these secondary compounds usually contain fewer organic remains than those above them, they are sometimes subdivided into two orders, one of which is considered to be intermediate between the primary and secondary strata. This is Werner's classification, of which we shall give an account in the next chapter.

SECT. XVIII. Secondary Limestone.

UNDER this title we shall comprehend what Werner calls transition limestone, floetz limestone, and limestone. Secondary limestone is a calcareous mass, sometimes granular, and sometimes compact, the former approaching to primitive limestone. Its fracture is scaly, and it is sometimes semitransparent. In colour it is very various, sometimes red, or rather blackish, with white veins, consisting of calcareous spar. It is often of a grayish cast. It sometimes forms vast blocks, without any appearance of stratification; at other times it is evidently stratified. It abounds with remains of marine animals, and often contains nodules of agate, and other similar stones.

A variety of calcareous stone is described by mineralogists under the name of swinestone. It is either compact, flaty, or porous, and is said in general to contain no petrifications, though some found in the mountain of Kinnecula contains many. It is considered by Kirwan as primeval limestone, impregnated with petroleum.

Limestone is sometimes found in ovoid balls, commonly containing a grain of sand in them.

There is a variety of limestone that is very porous, and abounds in remains of vegetable matter, as impressions of leaves, &c.

Secondary limestone is very abundant in most parts of the world, forming a considerable part of many mountains, and being often the principal stratum to a considerable depth below the surface. The mountain Iberg, in the Hartz, is composed of vast masses of it, irregularly rifted; and mountains of a similar kind are found in Siberia and in the Vivarais. In some of those mountains vast caverns have been formed. Secondary limestone mountains always repose on some primitive stone; thus, in Siberia their base consists of granite, porphyry or hornblende; in Saxony, of granite, or granular limestone, and sometimes of argillaceous schistus; in Switzerland, these mountains repose on argillaceous schistus or gneiss, or sometimes on calcareous puddingstone. In the Crimea, there is an immense extent of secondary limestone, between Rollof and

Perekop, which is minutely described by Pallas. Great part of the summit of Mont Perdu, the highest of the Pyrenees, is composed of secondary limestone, arranged in nearly vertical strata, and so full of the remains of marine animals as in some places to appear as if composed of nothing else. Here it seems to repose on granular limestone.

The base of Mount Ingleborough in Westmoreland, which is near 30 miles in circuit, consists entirely of limestone, containing vast quantities of sea shells. This stone also forms the principal inferior strata through the greater part of Derbyshire, being arranged in beds of various degrees of thickness, from a few inches to about 200 fathoms in some places, not having been perforated; and abounding with shells, and other marine remains.

It is found in many quarries in Scotland distinctly stratified. Mr Jameson notices quarries of limestone at Clovenburn, and Barjarg, and at Kellhead in Dumfriesshire.

Secondary limestone often contains metallic veins, especially in Derbyshire, where it abounds with galena, blende, sulphur pyrites, and copper pyrites. Sulphur is also sometimes found in it. Kirwan remarks, that in the rest of Europe limestone is seldom metalliferous.

The stone commonly called alabaster, employed in making statues and ornaments, is properly a carbonated lime, nearly allied to marble; though it is usually supposed to be a variety of gypsum or plaster stone. There is a gypseous alabaster that will be noticed presently.

Calcareous alabaster is not often white (though as white as alabaster is a common proverb), but generally tinctured with iron of a yellow, brown, or reddish cast. It is semipellucid, and usually so soft as to be scratched by the nail.

It is commonly found in blocks, in marble quarries, as in the island of Paros, and in several parts of Italy, particularly in the territory of Volterra in Tuscany, in Malta, &c. A variety is found in the form of stalactites of a conical or cylindrical form.

SECT. XIX. Gray Wacke.

GRAY wacke is a stone composed of fragments of quartz and argillaceous schistus, cemented by an argillaceous matter similar to the schistus, varying in size, from that of a hen's egg, till they are so minute as to be no longer visible. It sometimes contains a matter similar to siliceous schistus.

There is a variety of this stone, called by Werner gray wacke slate, which is a simple flaty stone, which bears a considerable resemblance to argillaceous schistus. From this, however, it is to be distinguished, according to Mr Jameson, by the following characters.

It has seldom a greenish or light yellowish gray colour, as is the case with primitive slate, but is usually ash and smoke gray. It does not show the silvery continuous lustre of primitive clay slate, but is rather glimmering, which originates from intermixed scales of mica. Quartz scarcely occurs in it in layers, but usually traverses it in the form of veins. Further we do not find crystals of feldspar, schorl, talc, chlorite slate, or magnetic iron stone are to be observed in it. It contains petrifications, particularly those varieties that border on gray wacke. It alternates with gray wacke.

These stones are distinctly stratified, but the direction of

Arrangement, &c. of the Materials of the Earth.

of their strata is not parallel to that of the other rocks on which they lie. They are very commonly found covering limestone, especially at the foot of mountains.

Gray wacke is found in Erzgebirge, at Braunsdorf, Riesberg, and Averbach, in Voegtländ, in Transylvania, on the banks of the Rhine, in Lahntal, and some other places in Germany. It is also found in Britain; and Mr Jameson notices it among the minerals of Dumfrieshire, where the gray wacke slate is found near Moffat, in the vicinity of Langholm, in the higher parts of the valley of Esk, and behind Burnswark. The strata found in these places yield a very good slate, nearly free from mechanical mixture, and well adapted to the roofing of houses.

Metals found in it.

This species of stone is rich in metals; the greater part of the veins of lead and silver in the Hartz, especially those of Clausthal and Zellerfeld, are in gray wacke. In Transylvania, in Vorespath, it contains even rich mines of gold. The gray wacke strata on the banks of the Rhine are also traversed by some metallic veins, but those of Saxony contain nothing but blind coal.

Several varieties of trap occur among the secondary strata, and must be here enumerated. They all consist principally of greenstone, or that mixture of hornblende and feldspar, which constitutes the primitive traps, noticed in Section XV. but in the traps we are now to mention, the mixture is much more intimate, the grains considerably finer, and the mass appears homogeneous. We shall here notice only three principal varieties; the amygdaloid or toadstone, the globular trap, and the greenstone, called by the Wernersians transition greenstone.

Amygdaloid or toadstone.

1. The amygdaloid, called in Derbyshire toadstone, and sometimes cat dirt, appears to consist of hornblende slate in a state of decomposition, and appears very similar to a kind of wacke, of a very fine grain. It is of a blackish colour, and very hard, and often contains a number of bladder holes, which are sometimes entirely empty, at others are partially or wholly filled with spar.

It runs in immense solid beds, without any appearance of stratification or fissure, of unequal thickness, having been seen from 6 feet to 600 thick. It commonly alternates with the strata of secondary limestone, as in Derbyshire, and sometimes seems to penetrate the inferior stratum of limestone to a very considerable depth. It contains no metallic veins, and it is said entirely to intercept those which it passes in the limestone strata. Saintfond affirms that lead ore is sometimes found in cat dirt; but he seems to have been deceived by the vagueness of the term, as the miners of Derbyshire give the same name to a greenish variety of limestone, which is sometimes traversed by veins of lead ore.

Globular trap.

2. Globular trap. This is a schistose greenstone, partially decomposed, and also resembles a fine-grained wacke; but it appears in the form of large balls, composed of concentric layers, with a hard nucleus. It is found at Altenzule in Voegtländ, and some other places. It sometimes contains veins of copper and iron.

Greenstone.

3. Greenstone. This is almost entirely composed of feldspar, usually of a pale flesh-red colour, having sometimes imbedded in it grains of grayish quartz, scales of

Arrangement, &c. of the Materials of the Earth.

iron, blackish mica, and crystals of pale flesh-coloured feldspar. This rock may be confounded with porphyry, or with feldspar; but is generally considered as different from both. Mr Jameson found it in beds from three to twelve feet thick on the upper side of the Sufanna vein in the valley of Leadhills, and in the mountain between Wamphray and Eskdalemuir.

These terms, like many others which we meet with in Sandstone. mineralogy, are very vague and indefinite, and are used to denote three or four kinds of stone; a calcareous, an argillaceous, and a siliceous sandstone. We shall here consider only two of them, the argillaceous and the siliceous.

1. Argillaceous sandstone. This is the sandstein Argillaceous of Werner, and the argillaceous grit of the ordinary sandminers. It is composed of grains of quartz, and sometimes of siliceous schistus; more rarely of feldspar. These grains are of various sizes, and are cemented in an argillaceous matter, commonly containing iron; whence this stone is sometimes called ferruginous sandstone. From the coarseness or fineness of the grains, it receives the names of coarse and fine sandstone. There is a very coarse kind found in Derbyshire, containing a considerable quantity of quartz pebbles.

This species of sandstone is found in immense beds, sometimes above 100 yards thick.

It is very distinctly stratified, and is commonly divided by fissures, into the shape of parallelopipeds. It sometimes alternates with layers of compact limestone, and often lies above a stone which we are immediately to mention, shale or spiss.

Sandstone is sometimes formed into globular concretions, composed of concentric lamellae.

Sandstone is one of the most abundant products of nature, occurring in almost every country. In Britain found, it forms the uppermost stratum in many parts of Derbyshire; and in the isle of Arran there is an immense separate mass of it, forming what is called the cock. * Jameson's Min. of the Isles, vol. I. p. 76.

The globular concretions of sandstone are uncommon. Mr Jameson observed them in the isle of Skye, near the harbour of Portree; and Reuss observed the same in Bohemia.

This species of sandstone usually contains many petrifications, but is generally not very abundant in metals; it however sometimes contains veins of cobalt.

2. Siliceous sandstone. This is a stone of a similar nature with the last, except that the cementing mass is sandstone, also of a siliceous nature. It is found in the ports of Domica and Campara, in the isle of Arbe, and on the coast of Dalmatia, where it contains petrifications. The hill of Platinburg consists of sandstone, with a chalcidony cement. Some fine specimens of siliceous sandstone are found in Salisbury Craigs at Edinburgh, containing shells which have assumed the nature of chalcidony. It does not appear to contain metals.

This is native sulphate of lime, and it appears in several forms. Six varieties are usually enumerated; common

Arrangement, &c. of the Materials of the Earth.

1. Common gypsum is a compact, granulated stone, commonly of a grayish colour, and mixed with impurities, containing a considerable quantity of carbonate of lime. Its texture is seldom laminated, but it appears like coarse loaf sugar. This kind is very abundant, many hills being entirely formed of it. Of these the most remarkable are the plasterhills in the neighbourhood of Paris, those in the canton of Bern in Switzerland, and others among the Alps. Hills of gypsum occur also in Spain and Poland; near the White sea; in Asia, where they are mostly in horizontal strata; in the north Archipelago, between Asia and America. Saussure found a mountain in Switzerland composed of gypsum, sand, and clay*. This kind sometimes contains petrifications, and often abounds with the impressions of animal and vegetable matters; some very curious examples of which will be mentioned in a future section. It contains few metals, although copper is sometimes found in it, as are rock-salt and sulphur.

2. Lenticular gypsum is a curious variety, which seems peculiar to Montmartre near Paris. In one of the banks in this mountain, specimens of it are found containing little lenticular bodies, distinct and disseminated through the stony matter, so as to form a great part of its mass. A specimen of this kind is figured by Patrin, in his natural history of minerals.

3. The crystallized gypsum is also found chiefly in the environs of Paris, in crystals that are decagonal, or sometimes like a rhomboidal octahedron, with the pyramids truncated near the base.

4. Fibrous gypsum, composed of short brittle threads disposed in bundles, is found in Derbyshire, and near Riom in Auvergne. A very beautiful variety of a silky feel, and reticulated texture, is described by Patrin, as found in Poland, in the salt mines of Wielitka; in Russia, near the junction of the river Oka with the Wolga; in Spain; and in China.

5. Gypsum with the appearance of vegetation is found in caverns near the baths at Matlock in Derbyshire. A beautiful specimen of it is figured by Patrin*.

6. Gypseous alabaster is very similar to true alabaster, except that it does not, like that, effervesce with acids, and is in general not so strong. It is found in great abundance in Derbyshire in large masses, filling up cavities in argillaceous grit. It never forms a stratum, but is generally attended with gravel, red clay, and shells. Mr Mawe represents the lower portions as being very strong and compact, so as to form columns and pilasters†. This kind is also found in Franche Comté, and on the Marne about six leagues from Paris at Lagny.

Though from the ordinary form or situation of gypsum, and the organic remains so commonly found in it, there can be no doubt of its being in most cases a secondary rock; yet from its having been found mixed

with mica in St Gothard, it is enumerated by some among the primary compounds.

This beautiful substance, which is native fluv of Fluor spar lime, is found either in large unformed masses or blocks, or crystallized in cubes or octahedrons. It is of different colours: but the most prevailing varieties are that in parallel zones or bands of green, blue, yellow, and white; and that in which a white ground is veined with a reddish brown. Some specimens are so shaded as to represent a geographical map; but these are very rare. It is so soft as to be easily turned in a lathe into those vases and other ornaments which are so commonly seen on chinurepices.

Fluor spar is found in several countries of Europe, but especially in France and Britain. According to found. Patrin, there are mines of it in the primitive mountains of Gyromagry, in the Vosges, in the neighbourhood of Langeac in Auvergne, and at Forez near Ambierle, that are inexhaustible‡. It is also found in the High. Nas. mountain of Pilat not far from Lyons; among the rocks that skirt the valley of Chamouni in the Alps; in the Altaichian mountains of Asia; and in Greenland.

The most productive mines of this substance in Britain are in a mountain near Castleton in Derbyshire. Here there are two mines producing the beautiful compact fluor, called Blue John, which is found in pipe veins running in various directions. The fluor commonly rests upon limestone, and it frequently has this stone for a nucleus, round which it appears to have crystallized. Frequently, however, the centre is hollow. In several parts of the mine the fluor is found in detached masses, in caves filled with clay and loose adventitious matter, having the appearance as if it had been broken off from the limestone on which it had been formed; for every piece, in one part or other, seems as if it had adhered to something, and been broken off.

Some of the pieces of fluor are a foot thick, and have four or five different veins or zones: such large pieces are however very rare, and in general they are only three or four inches thick*.

Saintfond, who has given an interesting account of the curiosities near Castleton, says, that fluor spar would be the most beautiful substance in nature, if it were but a little harder.

It is also found in Northumberland, in a vein among the granite mountains of Aberdeenshire†, and in one of the Shetland isles, in a vein of basalt‡.

Fluor appears in some cases to be primitive. Thus it is found forming whole strata in the mountains of the forest of Thuringia, and in a vein of quartz in Upper Hungary.

CHALK is too well known to require a description. Chalk. It is not always white, but is frequently coloured. It is disposed in horizontal beds that are often many yards in thickness, and which always repose on layers of other calcareous stone of a harder structure. These beds are often of considerable extent, and very common.

ly contain flints, ovoid limestone, and vast quantities of shells.

Chalk, which is so abundant in some countries, is scarcely found in others. It is well known that the south and south-eastern parts of England, and the south and south-west of France contain vast cliffs and beds of it; much of it is also found in Zealand. It is, we believe, a rare production in Scotland, and in most mountainous tracts. It has been remarked by Pennant, that if a line be drawn from Dorchester in the county of Dorset, to the county of Norfolk, it would form the boundary of the great chalky stratum of England; no quantity having been found to the north or west of that line.

There is a mountain of chalk between Tor and Ifum on the banks of the Donetz in Russia, in which some Greek monks have excavated apartments to the length of fifty fathoms.

No metals are found in chalk, though it is said that in France marital pyrites has been discovered in it.

SECT. XXV. Clay.

CLAY is found in various states with respect to hardness or solidity, from the soft ductile clay used by the potters and pipemakers to the perfect slate (clay slate, or argillaceous schistus) already described.

Soft clay is found in beds of various degrees of thickness, commonly not far below the surface, and alternating with harder clay, slates, sand, or limestone. It is generally very abundant, especially in those places where coal or rock-salt is found.

Clay of a harder consistency, commonly called indurated clay, or in the language of the miners clunch, is usually found below the softer clay, or there is sometimes a stratum of slate or similar argillaceous matter interposed. It often alternates with limestone, sandstone, or gypsum. Petrifications and shells are often found in it, as are quartz, sulphur pyrites, martial ochre, common salt, vitriol and alum.

A harder state of clay forms that substance which is called by mineralogists lithomarga (stone clay.) This is found in beds or strata often alternating with the former, with slate or with limestone, especially in coal mines. It also forms nests or balls in sandstone and similar rock. It sometimes bears the impressions of reeds and other vegetable bodies.

The next degree of hardened clay, forms slate clay, (Schiefer thon of the Germans.) This substance, however is not very hard, but is easily broken into angular tabular fragments. Its internal appearance is usually dull, but sometimes glimmering from a slight intermixture of scales of mica. Its colour is usually a yellowish gray, with spots or clouds of a pearl gray, or a cherry red, but sometimes it inclines to black. It usually lies between beds of sandstone, and almost always below the softer clays.

A kind of clay, of a still harder consistency, forms slate or schistus. This is usually of a dark brown or blackish colour, and a laminated texture. It lies in beds, sometimes of immense thickness, usually below sandstone, or alternating with this and limestone. It often contains impressions of organic remains, and there are sometimes found in it veins of lead ore. It is a very common stratum in the coal countries.

Nearly allied to this is what the miners call rubble stone, which is a common variety of slate found in similar situations with slate; but often very rich in metallic ores, especially iron, galena, bismuth, and cobalt. It also abounds with petrifications. It is sometimes found in primitive rocks.

SECT. XXVI. Marl.

MARL is a substance chiefly composed of sand, clay, and calcareous matter, which is found in many places, and forms one of the most valuable natural manures used in agriculture. This is also found of various degrees of hardness, from a soft powder to a stony consistency, in which last state it forms what Kirwan calls marlite. In colour it is usually of a reddish white, sometimes verging upon red, and it is not unfrequently found of a yellowish brown or blackish cast. Marl is usually disposed in considerable beds of various degrees of thickness, in valleys and other low lands, especially among the coal strata. Indurated marl occurs in the coal strata of Mid Lothian, and it is also found in the island of Ilay. Powdery marl is seen in Skye.

Stony marl, or marlite, is found in Bavaria, alternating with sand and sandstone. Hills of it occur in Carniola, Carinthia, and the Venetian territory. It is also found between strata of limestone and argillaceous schistus.

SECT. XXVII. Argillaceous Ironstone.

THIS is sometimes called metal stone, and is very common in the coal countries. It is very heavy and compact, and of various colours, from a dark brown to a blood red; the latter forms the haematites or bloodstone, one of the richest iron ores. It often contains in it spherical balls like iron bullets. It is disposed in strata alternating with indurated clay, slate clay, marl, or sandstone, seldom far below the surface. It seldom forms very extensive beds, but is often confined to particular spots.

Ironstone is found in great abundance in Cumberland, and in most parts of Scotland. It may be seen in the cliffs all along the coast of Fife, from Dysart to St Andrews.

SECT. XXVIII. Wacke and Basalt.

WE have already spoken of several stones under the name of traps, that are found both among primitive and secondary compounds. The two substances which we are now to notice are nearly allied to the traps, and have been classed with them under the general name of whinstone. This is a favourite term among the mineralogists of Scotland, of whom Sir James Hall employs it as a generic name to denote trap, basalt, wacke, grunstein, and porphyry. The term is convenient, but Professor Jameson and others of the Wernerian school object to it as too vague and indefinite.

Wacke, or wacken, differs from trap only in being more compact and of a finer grain. It is heavy and very hard, so as often to strike fire with steel; it is dull and opaque, and breaks with an even fracture. Its colour is usually a reddish brown or gray of various shades.

Arrangement, &c. of the Materials of the Earth.

shades, and sometimes it has a greenish cast. It has usually an earthy smell, when breathed on. It is sometimes highly impregnated with iron, and often contains crystals of hornblende, and very commonly those of hexagonal black mica.

It often forms a considerable part of mountains, either in vast blocks, as in the hill on which Edinburgh castle stands, or in strata lying above limestone or sandstone, or alternating with these. A great part of the Calton-hill, of Salisbury craigs, and Arthur's seat at Edinburgh, is composed of strata of this kind; and similar appearances take place in the bed of the water of Leith near the town, and in the cliffs on the coast of Fife, especially at St Andrews. To the eye of the volcanic Saintfons, all these beds appeared to be lava. We are disposed to think, with Mr Playfair, that the curious instance of alternate strata of basalt (as Saintfons calls it) and limestone, near Villeneuve de Berg, described and figured by that author, affords an example of whinestone alternating with limestone, such as are seen in Scotland. Several varieties of wacke are found in the hills near Edinburgh, and are described by Dr Townson. Mr Jameson observed wacke alternating with porphyry in Skye.

Basalt has a finer grain, and is more compact, than even wacke, and is the most dense of all the whins or traps. It is found either in large blocks, covering the other strata, sometimes in the form of tables, or in regular prismatic columns, either straight or bended. We have already treated so fully of the nature, properties, and chief habits of basalt (see BASALTES), that little remains to be added here.

It is principally distinguished from wacke, where it is not in regular prisms, by very rarely containing crystals of mica, which are so common in the latter.

Saintfons in his splendid work Sur les Volcans eteints du Vivarais, &c. has figured some examples of basaltic pillars which rival those of Staffa and the Giants Causeway. A more romantic situation is scarcely to be conceived than that drawn in his eleventh plate, of a village placed in the front of a bold hill covered with bundles of small pillars lying in every direction, and having detached perpendicular columns standing at each end, with a large cave directly behind the houses. Large masses of basalt are seen in the north of Shetland, standing insulated, and assuming a very grotesque appearance. Mr Jameson describes one of these in the isle of Jura, that forms a natural arch. We remember seeing two curious insulated rocks on the shore at the foot of Kinkeld braes at St Andrews, but do not recollect whether they are of a basaltic nature.

Several other substances, as sand, gravel, peat, &c. might here be noticed, but their structure and situation are too well known to render a particular notice necessary.

Many of the stones which we have described among the primitive rocks, are also sometimes found among the secondary strata, as argillaceous schistus, hornstone, hornblende, jasper, and especially puddingstone; but they are not so important as to require a second examination.

Before we conclude this general account of the materials which compose our globe, we must briefly notice two of the most valuable mineral productions, viz. rock

salt and coal, and must say something of fossils and petrifications.

SECT. XXIX. Rock Salt.

Rock salt or sal gem, (the steinfal of the Germans) is the purest muriate of soda that is found in nature, it being much less impregnated with foreign matters than what is procured from sea water. It is very hard, and generally very transparent, being sometimes as clear as crystal. It is usually white, but often yellowish, blue, red, or violet, and now and then it is quite opaque. This salt forms in the bowels of the earth horizontal beds or banks, more or less thick, from a few inches to many hundred fathoms; and sometimes extending several miles round. It commonly alternates with clay or gypsum. The beds are sometimes without any break for a great extent. It is generally found a few fathoms below the surface, and in some places is found continued to the depth of 1000 feet.

It is found in some mountains; and in Algiers, near the lake called Marks, there is a mountain almost wholly composed of it. The famous salt mine of Wielitiska in Austrian Poland, about eight miles to the south-east of Cracow, is in the northern extremity of a branch of the Carpathian mountains. The salt found here is of an iron gray colour, intermingled with white cubes; and sometimes large blocks of salt are found imbedded in marl. This famous mine has been worked ever since 1251, and it is pretended that its excavations extend more than a league from east to west. About five leagues to the south-east of Cracow are the salt mines of Bosnia, the depth of which is nearly equal to those of Wielitiska (1000 feet); but the salt procured from them is less pure. Mines of salt, in horizontal undulated beds, occur at Thorda in Transylvania, and in Upper Hungary. In the side of a mountain, about two leagues from Halle, on the banks of the Inn, to the north-east of Inspruck, rock salt is found imbedded in layers of a slaty rock; but there is one part of the mountain in which there occurs an immense body of salt, without any mixture of rock, to which they pass by a gallery 260 toises in length, closed at the end with a locked door. This salt is very impure. There are three important salt mines in Spain; the first near Mingranella, in a mountainous tract, between Valentia and Castile, imbedded in layers of gypsum; the second in Spanish Navarre, in a ridge of hills composed of limestone and gypsum; and the third that of Cardona in Catalonia, about 16 leagues to the north-east of Barcelona, which is one of the most curious natural productions with which we are acquainted. It consists of an immense solid rock of salt, elevated 500 feet above the earth, and extending to a depth that has not been ascertained. It is without crevices or clefts, and has no appearance of strata, and is near a league in circuit. There is no plaster or gypsum found in the neighbourhood, and the salt rock is as high as any of the adjacent hills.

Rock salt is found in several places in England, particularly at Northwich in Cheshire, at Droitwich in Worcestershire, and near Welton in Staffordshire; but the mines in Northwich are the most productive. Salt mines, in this situation, were known to the Romans; at North-

Arrangement, &c. of the Materials of the Earth.

but the principal mine that is at present wrought, was discovered in the beginning of last century. It forms immense quarries, extending over several acres, which, with their huge crystal pillars and glittering roof, present a most beautiful spectacle. The salt found here is of a dark-brown colour, like brown sugar candy, and is so hard that it is blasted with gunpowder to get it from the mafs. It is disposed in beds, alternating with beds of clay, gypsum, and flaty stone. Salt is procured at the greatest depth hitherto explored; and wherever a shaft is sunk in the neighbourhood, there is a certainty of finding salt*.

Besides these extensive mines, rock salt is found in the canton of Berne in Switzerland, in Siberia, in Arabia, in Tibet, and even in New Holland. It is also found in many parts of America, at a great height in the mountains, especially those of Peru.

WE have already, in the articles COAL and COALERY, treated of the nature of this substance, of the strata that are usually found connected with it (according to the phraseology of the miners), and of the method of procuring it from the pits; and, in MINERALOGY, we shall give a particular account of the several varieties, and the distinguishing characters of each. A few observations respecting the principal collieries, with the appearance of the coal found in them, and the corresponding stratification, fall to be made in this place.

There are certain general circumstances that attend the depositions of coal in almost every place where it is found, and which we must mention before noticing the particular collieries. These are as follows.

1. The beds in which coal is disposed, usually have their extremities near the surface of the ground, from which they bend obliquely downwards, the middle part of the bed being nearly horizontal, so that a vertical section of the bed nearly resembles the keel of a boat. This figure is well expressed in the first and third plates to Mr Jameson's Mineralogy of Dumfries. The lowest part of the bed is usually the thickest (D).

2. A bed of coal is seldom found single; but, in general, several strata occur in the same place, of various thickness, the upper being usually very thin, and the lower very thick, with several stony strata between each two. Where there is only one bed, this is generally of very considerable thickness. At Whitehaven there are found at least 20 coal strata below the surface; and at Liege, in France, there are no less than 60.

3. The strata that separate the layers of coal are nearly the same in every colliery, and will be seen by referring to the table given under COALERY, and by those which will immediately be added. Those strata which are in immediate contact with the coal, are either whinstone, or more commonly an argillaceous flaty mafs; and near this is sandstone, in layers that are separated by flaty clay, mixed with particles of coal.

4. It is an observation which holds, almost without exception, that the flaty strata, and especially those next the coal, bear the impression of vegetables, and often of exotic or unknown plants.

Coal, in a greater or less quantity, but of very different qualities, has been found in most countries, and perhaps exists in all. It is found in France, Holland, Britain, Germany, Saxony, Portugal, Switzerland, and Sweden; in China, Japan, and in New Holland; and much of it is worked in Virginia in America. But France and Britain may be considered as the favourite seats of this invaluable commodity, which may justly be put in competition with the treasures of Potofi and Peru.

It is stated by Buffon, that there are no fewer than 400 collieries worked in France; and yet Saintfond regrets that his countrymen are not so far advanced in the use of this mineral as the inhabitants of Britain*. The most considerable coal mines in France, are those in the Lyonnais, at Forez, Burgundy, Auvergne, Languedoc, Franche Comté, and Liege.

The mines in the Lyonnais, and those of Forez, are among the most important in France. They are situated in a valley, extending from the Rhone to the Loire, in a direction from north-east to south-west, between two chains of primitive mountains, and they occupy in length a space of six or seven leagues, from Rive-de-Gier to Firmini. In one part of the valley, in the neighbourhood of Saint-Etienne, the strata are nearly horizontal, and the medial thickness of the coal stratum is from three to six feet; and near the Loire there are from 15 to 20 of these. At Rive-de-Gier the strata are almost vertical, and their thickness is very unequal, being seldom less than three feet, and sometimes amounting to 40 or even 60. All the coal produced by these mines is of an excellent quality, and its quantity is immense. Patrin states, on the most undoubted authority, that there are in the neighbourhood of Rive-de-Gier, no less than 40 mines at work, which produced in one year 1,600,000 quintals of coal†.

The next in importance are the coal mines of Liege. The beds of coal in that country have a direction from v. east to west; they commence about a league to the east of the town, and extend to about a league and a half to the west of it. Here, after meeting with some interruption, they extend for several leagues farther. Their breadth, from north to south, is about three-fourths of a league. At Verbios, which is to the north-west of the city, there are, according to Jars, more than 40 strata of coal, which are separated from each other by beds of different kinds of sandstone, of from 30 to 100 feet in thickness†. Genneut has counted 61 of these beds, placed one above another; and he is of opinion, that the lowest penetrates to the depth of 4000 feet perpendicular. Though these mines have been wrought from the 12th century, they have not yet reached to more than the twenty-first bed, at the depth of a little more than 1000 English feet.

(D) Saintfond, in the section which he has of the coal strata at Newcastle, describes them as if they were convex towards the upper surface. (See p. 134. of vol. i. of the English Translation of his Travels in England, &c.) Surely this is a mistake.

The principal collieries of Britain are those of Newcastle and Whitehaven.

Newcastle is surrounded by collieries to the distance of six or seven leagues, and may, perhaps, be considered as the richest coal district in the world. There are in several of the Newcastle mines not fewer than 16 beds of coal, two of which are considerably thicker than the rest, being each about a fathom in thickness. These are called the main coal, and are distinguished into the high main coal, and the low main coal, separated from each other by a considerable number of stony strata. Good coal, in sufficient quantity, is generally found at the depth of little more than 100 feet. The bed is five feet thick in some places, and less in others; but, in general, it is easily wrought, and large pieces are brought up. This last circumstance is of considerable advantage, as these pieces are most proper for chamber fires, and easily transported, which makes this kind of coal sell at a higher price. Where the bed of black and bituminous clay is penetrated, the coal is found adhering to it: but this is not always the case, for there are other mines in the neighbourhood where freestone is recovering, which, in the points of contact, is mixed with coal to the thickness of two or three inches; the latter running, as it were, in splinters into the stone, and having a ligneous appearance, when attentively examined †.

At Whitehaven, the beds of coal lie in a direction parallel to each other. Their inclination or dip is nearly to the west, and is from one yard in eight, to one in twelve. The strata are frequently interrupted by large fissures, or dykes, some of which remove the strata upwards or downwards, 120 feet. The course of these fissures is almost east and west. In a depth from the surface of 165 and a half fathoms, there are, in these collieries, seven large beds of coal, and 18 thin

beds, which cannot, at present, be rendered profitable.

The strata superincumbent on the large beds of coal are, 1st bed, Blue slate. 2d, Gray freestone. 3d, Hard, white freestone. 4th, Blue slate, striated or speckled with freestone. 5th, Gray slate. 6th, Hard, white freestone.

The strata immediately beneath these large beds of coal, are from one and a half to six inches thick, and consist of a species of argillaceous earth, or shale. As this earth is of a very soft or friable nature, the weight of the superincumbent strata presses the pillar of coal through it. If the pillar descends a few inches, the roof not equally yielding at the same time, crumbles, or breaks into small pieces. When, under these circumstances, the thickness of the bed does not exceed six feet, nor the depth 30 fathoms, the surface of the earth is sensibly affected *.

There appear to be two principal belts of coal in this island, extending from the eastern to the western coast; one from Newcastle to Whitehaven; the other from the east coast of Scotland, across the vale of Forth and Clyde, to Ayrshire. Coal is indeed found in many other parts of the island; but the quantity is very trifling.

The similarity of situation, and the similar nature of the coal at Whitehaven and Newcastle, would naturally lead us to infer, that the coal at both places is from the same seam. But this is placed beyond dispute, by a comparative examination of the strata in both situations. We shall here give two tabular views of the strata, one taken from Saintfons's Travels, and the other from Dr Joshua Dixon's account of the Whitehaven mines, in his literary life of Dr Brownrigg. Allowing for the different names given by different miners to the same substances, and Dr Dixon's greater minuteness, there is a wonderful similarity between the two tables.

TABLE I. Strata in Restoration Pit, St Anthon's Colliery, Newcastle, to the depth of 135 fathoms.—
From Saintfons.

An interesting and valuable memoir on the subject of coal, written by M. Duhamel the younger, was presented a few years since to the Academy of Sciences at Paris, who adjudged it the prize that had been offered for the best essay on the subject. An ample abstract of this memoir appeared in the Journal des Mines, N^o vii. In this paper is given a table of the number of veins, their direction and inclination, and the nature of the strata next the coal, and in the neighbourhood, in all the principal mines in Europe.

SECT. XXXI. Of Fossils and Petrifications.

THOSE organic remains of vegetable and animal matter which are found below the surface of the earth, mixed with the stony matters which are properly the component parts of the earth, are generally called fossils, or extraneous fossils. If they have entirely lost all traces of vegetable or animal matter, and have assumed a stony earthy nature, they are called petrifications.

Some of these organic remains, particularly those of the vegetable kind, are found penetrated with a bituminous substance, so as to be rendered highly inflammable. One of the most curious circumstances attending these fossil bodies is, that they are very commonly natives of a different country from that in which they are found, or are the remains of species that are now no longer known.

We may properly divide these substances into those of the vegetable and those of the animal kingdom.

1. Vegetable fossils. Almost every part of vegetables, the trunks, branches, leaves, and fruits, have been found in a fossil state, or impressions of some of them are seen in various mineral substances, especially in the slaty stone which accompanies coal.

Fig. 6. represents a curious example of this, that was found in the mines at Saint Etienne in France.

A, is a fruit resembling that of coffee.

B, is a portion of an unknown vegetable, apparently of the verticillate tribe.

C, is a species of fern, which is very remarkable, as it is furnished with fructifications.

D, is part of a plant with verticillate leaves, probably a species of gallium.

E, is some exotic fruit.

Whole trees are often found below the surface of the earth, especially in bogs and mosses, sometimes retaining much of their vegetable nature, but more commonly either impregnated with bitumen or completely petrified. Subterranean trees are frequently dug up in the isle of Anglesea; and in the isle of Man there is a marshy six miles long and three broad, in which fir trees are found in great quantities; and though they are 18 or 20 feet below the surface, they appear as if standing firmly upon their roots. Subterranean trees, in various states, are frequently found in Ireland, especially in the neighbourhood of Lough Neagh. Much has been written on the subject of these petrifications of Lough Neagh, by Dr Boate, in his Natural History of Ireland; by Mr Molyneux, in the Philosophical Transactions, N^o clviii. and Dr Barton in his Lectures on Natural Philosophy. Some of these trees are represented as of an immense size*. One of the most curious instances of vegetable fossils, is that related by Rammazzini, as seen by him

at Modena in Italy. At the bottom of wells, that are dug there below stony masses, which appear to have been the foundation of a former city, at the depth of near 30 feet, they find heaps of wheat entire, silbert trees, with their nuts, briars, &c. They find, likewise, every six feet, a layer of earth, alternating with branches and leaves of trees.

At the depth of 28 feet, or thereabouts, they find a chalk that cuts very easily. It is mixed with shells of several sorts, and makes a bed of about 11 feet. After this they find a bed of marly earth, of about two feet, mixed with rushes, leaves, and branches. After this bed comes another chalk bed, of nearly the same thickness with the former, which ends at the depth of 49 feet.

That is followed by another bed of marly earth like the former; after which comes a new chalk bed. These successive beds of marly earth and chalk are to be found in the same order, in whatever parts of the earth they dig. The auger sometimes finds great trees, which give the workmen much trouble. They see also sometimes at the bottom of these wells, great bones, coals, flints, and pieces of iron†.

These vegetable fossils are generally of a flinty structure, being sometimes rough and sandy; at others so hard and compact as to admit of a fine polish. Some beautiful specimens of petrified wood, of the appearance of agate, are to be seen in the cabinet of natural history. That of Biflon at Paris contains two examples of this kind, which are figured at fig. 7 and 8. Fig. 7. is a transverse section of a piece of agatized wood, in which the ligneous texture is most completely preserved. Fig. 8. is another more compact, and which has the additional singularity of containing several worms. The white oval spots are supposed to have been eggs, from which the worms had issued.

Among the bituminous vegetable fossils, none have attracted more attention than what is called bovey coal, a substance of an intermediate nature between wood and peat, which is dug up in a common near Chudleigh in Devonshire. It is of a laminated texture, of a chocolate, or sometimes of a shining black colour, like deal boards that had been half charred. It burns heavily, and consumes to light gray ashes. It is regularly stratified among beds of sand and clay, and the beds of coal are sometimes of considerable thickness. Mr Parkin-
son has collected much information respecting the former and present state of this coal, in his entertaining work on fossils‡.

2. Animal fossils. Fossils of animal matters are still more common than those of vegetables. Shells and bones are found in almost every bed of limestone, and in almost every country, at the bottom of the deepest valleys, and at the tops of very considerable mountains.

In the limestone strata in Derbyshire are found many of those fossils, which are called star-stones and scraw-stones, which appear to be the remains of marine animals called encrini. These are described by Whitehurst, who has given figures of similar animals brought entire from the West Indies§. Fig. 9. represents one of these stones.

The isle of Cherea in Dalmatia contains caverns in which are found prodigious quantities of fossil bones of oxen,

oxen, horses, and sheep. Similar examples occur in many places; but human bones are, we believe, never found in a fossil state.

Fossil shells are found on the Alps, on the top of Mount Cenis, on the Apennines, on the mountains of Genoa, and in most of the quarries of stone and marble in Italy; in most parts of Germany and Hungary, and indeed generally in all the elevated places in Europe. We also find them in the stones whereof the most ancient edifices of the Romans were constructed.

In Switzerland, Asia, and Africa, travellers have observed petrified fish, in many places; for instance, on the mountains of Castravan, there is a bed of white laminated stone, and each lamina contains a great number and diversity of fishes; they are, for the most part, very flat, and extremely compressed, in the manner of fossil fern; yet they are so well preserved, that the minutest marks of their fins and scales are distinguishable, and every other part, whereby one species of fish is known from another.

There are likewise many echinites and petrified fish between Iver and Cairo, and on all the hills and heights of Barbary, most of which exactly correspond with the like species taken in the Red sea.

The long chain of mountains which extend from east to west, from the lower part of Portugal to the most eastern parts of China, those which stretch collaterally to the north and south of them, together with the mountains of Africa and America, which are now known to us, all contain strata of earth and stone, full of shells.

The islands of Europe, Asia, and America, wherein Europeans have had occasion to dig, whether in mountains or plains, all furnish us with shells, and convince us that they have this particular in common with their adjacent continents.

The glossoptra, or the teeth of sharks and other fishes, are found in the jaws, polished and worn smooth at the extremities, consequently must have been made use of during the animal's life; and in shells the very pearls are found, which the living animals of the same kind produce.

It is well known that the purpura and pholades have a long-pointed proboscis, which serves them as a kind of gimblet or drill, to pierce the shells of living fish, on whose flesh they feed. Now, shells thus pierced are found in the earth, which is another incontestable proof that they heretofore inclosed living fish, and that these fish inhabited places where the purpura and pholades preyed on them.

In Holland sea shells are found 100 feet below the surface; at Marly-la-Ville, six leagues from Paris, at 75; and in the Alps and Pyrenean mountains they are found under beds of stone of 100, nay even 1000 feet.

Shells are likewise found in the mountains of Spain, France, and England, in all the marble quarries of Flanders, in the mountains of Guelders, in all the hills round Paris, in those of Burgundy and Champagne; and, in short, in all places where the basis of the soil is neither freestone nor sandstone.

By shells we would be understood to mean, not only those which are merely testaceous, but the relics of the crustaceous fishes also; and even all other marine productions; and we can venture to assert, that, in the ge-

nerality of marbles, there is so great a quantity of marine productions, that they appear to surpass in bulk the matter whereby they are united.

Among the many instances of the multiplicity of oysters, there are few more extraordinary than that immense bed which M. de Reaumur gives an account of, which contains 130,630,000 cubic fathoms. This vast mass of marine bodies is in Touraine in France, at upwards of 36 leagues from the sea. Some of these shells are found so entire, that their different species are very distinguishable.

Some of the same species are found recent on the coast of Poictou, and others are known to be natives of more distant parts of the world. Among them are likewise blended some fragments of the more strong parts of sea plants, such as madriporis, fungi marini, &c. The canton of Touraine contains full nine square leagues in surface, and furnishes these fragments of shells wherever you dig.

Near Reading in Berkshire, a continued body of oyster shells has been found: they lie in a stratum of greenish sand, about two feet in thickness, and extend over five or six acres of ground; they are covered by strata of sand and clay, upwards of 14 feet deep. Several whole oysters are found with both their valves or shells lying together, as oysters before they are opened; the shells are very brittle; and in digging them up, one of the valves will frequently drop from its fellow. Several are dug out entire; nay, some double oysters with their valves united.

In a quarry at the east end of Broughton in Lincolnshire, innumerable fragments of the shells of shell fish, of various sorts, are found under a stratum of stone imbedded in clay, with pieces of coral, and sometimes whole shell fish, with their natural shells and colours: some are most miserably cracked, bruised, and broken; others totally squeezed flat by the incumbent weight of earth.

Sharks teeth are dug up in the isle of Sheppey, retaining their natural colour, not petrified.

The teeth of sharks have likewise been taken out of a rock in Hinderthelf park, near Malton in Yorkshire.

In the isle of Caldey, and elsewhere about Tenby in Pembrokeshire, marine fossils have been found in solid marble, on the face of the broken sea cliffs, 200 fathoms below the upper surface of the rocks. Nor were they only observed upon the face of these rocks, but even more or less throughout the whole mass or extent of them. This is manifest from divers rocks hewn down by workmen for making of lime, and other pieces casually fallen from the cliffs.

Thousands of fossil teeth, exactly answering to those of divers sorts of sea fish, have been found in quarries and gravel pits about Oxford.

At Tame in Oxfordshire, the belemnites, or thunderbolt stones, are found in a stratum of blue clay, which still retain their native shelly substance.

The belemnites found in gravel pits, have suffered much, by their being rubbed against each other in the fluctuation of waters.

The nautili and belemnites are frequently found at Gorling near Oxford*.

One of the most extraordinary collections of shells is Transf. vol. that liv. p. 5.

* PML

Arrangement, &c. of the Materials of the Earth. that lately discovered by Ramond on the summit of Mont Perdu, the highest of the Pyrenees, where there are found vast quantities of sea shells and other marine spoils, and even skeletons of animals, in a fossil state.

Whole skeletons of very large animals have been discovered in a fossil state. Those of elephants have been found buried in the plains of Siberia; and bones of the rhinoceros, the hippopotamus, and the tapir, have been found in other places. A very large skeleton, nearly complete, of an immense animal, similar to the rhinoceros, is preserved in the cabinet of Madrid. It was dug up at Paraguay in South America, at the depth of 100 feet, in a sandy bed, on the banks of the river de la Plata. A description and engraving of it are given by Cuvier, in the Annals of the National Museum, N^o 29. It appears to be at least 12 feet long, and the bones are of an immense size.

A prodigious quantity of fossils, both of marine animals, and of quadrupeds, are found in the plaster hills of Montmartre near Paris. An account of these has lately appeared in several numbers of the Annals of the National Museum, by M. Lamareck, accompanied with the anatomical illustrations of Cuvier. These papers are extremely curious, and contain engravings of most of the fossils described, some of which are the remains of unknown animals. Our limits do not permit us to present our readers with even an abstract of these accounts. We shall therefore select only one example.

Fig. 10. represents a block of gypsum, on the surface of which is the skeleton of an animal resembling a mouse, or, according to Cuvier, one of the opossum

tribe. The skeleton is nearly entire, and the head, the neck, the spine, the pelvis, one of the fore and hind legs, and part of the tail, are very distinct. There were two pieces of gypsum found together, which appear to have divided the skeleton between them. The animal seems to have been crushed or imbedded in his natural situation *.

We have now enumerated the principal materials that compose the external crust of our earth, and have mentioned some of the most material circumstances respecting each. The metallic ores still remain to be considered, and they shall be noticed in describing metallic veins.

CHAP. II. General Distribution of the Materials of the Earth.

THE uppermost stratum of the earth, in low situations, is, for the most part, composed of sand or clay, or a mixture of these, forming beds that are either composed of the same mixture, or of alternate layers of the two substances. These beds vary in thickness, in different places; but, in the same place, they usually preserve nearly the same thickness for a considerable extent. Sometimes these beds of clay, sand, and earth, with shells, extend to the depth of some hundred feet. See the annexed table, 1. (x).

This table exhibits a view of the arrangement of strata in several countries of Europe; and, with the tables of coal strata, in the last chapter, will give the reader more information on this subject than an elaborate detailed account.

(x) The following works are referred to in the table of strata.

• * Varenii Geogr. Gener. lib. i. prop. vii.
• † Buffon, Nat. Hist. vol. i. art. vii.
• ‡ Bergman, Descript. Phys. de Terre, sect. viii.
• || Kirwan, Geolog. Essays, p. 259.
• § Guettard, Atlas Mineral. de la France,
• ¶ Whitehurst's Theory of the Earth, sect. xvi.
• ** Ib. sect. xix.

In our subsequent view of the distribution of the stony matters that compose the earth, we shall consider,
1. The nature, disposition, and structure, of mountains.
2. The nature, direction, &c. of dykes.
3. The nature, direction, &c. of metallic veins.

SECT I. Of Mountains.

THERE are no objects on the surface of the earth which are so well calculated to excite the attention of mankind in general, and that of geologists in particular, as those stupendous elevated masses which we call mountains. The term mountain has in general been applied to those parts of the earth which are elevated to a very considerable height above the level surface; and a mountain is in common language distinguished from a hill only by its superior elevation. But as it is found necessary in a scientific point of view to render this distinction more accurate and precise, various geologists have given more correct definitions. By Pini and Mitterpachter every elevation whose declivity makes with the horizon an angle of at least 13°, and whose perpendicular height is not less than one-fifth of the declivity is called a mountain. Werner distinguishes mountains according to their height, into high, middle-fixed, and low. A high mountain according to him is that whose perpendicular height exceeds 6000 feet; when the height is not above 6000 nor below 3000 he calls it middle-fixed; and when its height is below 3000 feet, he calls it low.

Mountains are either single or in groups; and these groups either consist of several mountains standing near each other so as to occupy nearly the centre of a certain space of ground, or they follow each other so as to form a ridge or chain running across a country, or along its shores. Sometimes these chains run in a longitudinal direction, as is the case with Mount Caucasus and the Uralian mountains in Asia, the Cordilleras in South America, &c. but often they run in a curvilinear direction like a crescent, as the Carpathian mountains, which separate Hungary from the rest of the Austrian territories. It has been supposed by some theoretic writers, that chains of mountains always run in nearly the same direction, which has been conceived to be from east to west; but this is by no means exact, as later observations have shown that they assume different directions according to the form of the country where they are situated. Some writers have laid it down as a general rule, that chains of mountains always extend in a direction nearly parallel to the length of the country; but to this there are also many exceptions. Thus the Uralian mountains, the Carpathians, the Pyrenees, the Grampians in Scotland, and many others, run rather across the country. It often happens that mountains occupy nearly the central parts of a country; and the land generally slopes with a gentle declivity towards one side of the chain, while towards the other it is considerably steeper. This circumstance of one side of a chain of mountains being steeper than the other, has been lately extended to mountains and hills in general; and Dr Kirwan has written an excellent paper on the subject, from which we shall here extract the most important observations.

"That one part of almost every high mountain or hill is steeper than another, could not have escaped the notice of any person who had traversed such mountains; but that nature in the formation of such declivities had any regard to different aspects or points of the compass, seems to have been first remarked by the celebrated Swedish geologist Mr Tilas, in the 22d vol. of the Memoirs of Stockholm for 1760. Neither Varennius, Lulolph, nor Buffon in his natural history publications in 1748, have noticed this remarkable circumstance.

"The observation of Tilas, however, relates only to the extreme ends, and not to the flanks of mountains; The steep with respect to the former, he remarked that the steep side faces est declivity always faces that part of the country where the land lies lowest; and the gentlest, that part of the country where the land lies highest: and that in the southern and eastern parts of Sweden they consequently face the east and south-east; and in the northern the west. The essential part of this observation extends therefore only to the general elevation or depression of the country, and not to the bearings of their declivities.

"The discovery that the different declivities of the Western flanks of mountains bear an invariable relation to their different aspects, seems to have been first published by Mr Bergman in his Physical Description of the Earth, of which the second edition appeared in 1773. He there remarked, that in mountains that extend from north to south, the western flank is the steepest, and the eastern the gentlest. And that in mountains which run east and west the southern declivity is the steepest, and the northern the gentlest. Vol. II. § 187.

"This assertion he grounds on the observations related in his 1st vol. § 32, namely, that in Scandinavia, the Suevoberg mountains that run north and south, separating Sweden from Norway, the western or Norwegian sides are the steepest, and the eastern or Swedish, the most moderate; the verticality or steepness of the former being to that of the latter as 40 or 50 to 4 or 2.

"That the Alps are steeper on their western and southern sides than on the eastern and northern.

"That in America the Cordilleras are steeper on the western side, which faces the Pacific ocean, than on the eastern. But he does not notice a few exceptions to this rule in particular cases which will hereafter be mentioned.

"Buffon, in the first volume of his Époches de Nature, published in 1778, p. 185, is the next who notices the general prevalence of this phenomenon, as far as relates to the eastern and western sides of the mountains that extend from north to south; but he is silent with respect to the north and south sides of the mountains that run from east to west; nay, he does not seem to have had a just comprehension of this phenomenon; for he considers it conjointly with the general dip of the regions in which these mountains exist. Thus he tells us, vol. i. p. 185, that in all continents the general declivity, taking it from the summit of mountains, is always more rapid on the western than on the eastern side; thus the summit of the chain of the Cordilleras is much nearer to the western shore than to the eastern; the chain which divides the whole length of Africa, from the Cape of Good Hope to the mountains of the Moon,

General Distribution of the Materials of the Earth.

Moon, is nearer, he says, to the western than to the eastern seas; of this, however, he must have been ignorant, as that tract of country is still unknown.

"The mountains which run from Cape Comorin through the peninsula of India are, he says, much nearer to the sea on the east than on the west; he probably meant the contrary, as the fact is evidently so, and so he states it in vol. ii. p. 295; the same he tells us may be observed in islands and peninsulas, and in mountains.

"This remarkable circumstance of mountains was notwithstanding so little noticed, that in 1792 the author of an excellent account of the territory of Carlsbad in Bohemia, tells us he had made an observation, which he had never met with in any physical description of the earth, namely, that the southern declivity of all mountains was much steeper than the northern, which he proves by instancing the Erzgebirge of Saxony, the Pyrenees, the mountains of Switzerland, Savoy, Carinthia, Tyrole, Moravia, the Carpathian and Mount Heemus in Turkey. 2. Bergm. Jour. 1792. p. 385, in the note.

"Herman in his geology, published in 1787, p. 90, has at least partially mentioned this circumstance; for he says that the eastern declivities of all mountains are much gentler and more thickly covered with secondary strata, and to a greater height than the western flanks, which he instances in the Swedish and Norwegian mountains, the Alps, the Caucasian, the Appenine, and Ouralian mountains; but the declivities bearing a southern or northern aspect he does not mention.

"Lamethetic, in vol. iv. of his theory of the earth, of which the second edition appeared in 1797, a work which abounds in excellent observations, p. 381, produces numerous instances of the inequality of the eastern and western declivities, but scarce any of the northern and southern, whose difference he does not seem to have noticed; but he makes a remark which I have not seen elsewhere, that the coasts of different countries present similar declivities.

"With regard to eastern and western aspects, he thinks that a different law has obtained in Africa from that which has been observed in other countries; for in that vast peninsula he imagines the eastern declivities of mountains are the steepest, and the western the gentlest. Of this, however, he adduces no other proof, but that the greatest rivers are found on the western side: this proof seems insufficient, as, if mountains be situated far inland, great rivers may flow indiscriminately from any side of them, and sometimes few rivers flow even from the side whose descent is most moderate; for instance, from the eastern side of the mountains of Syria. The Elbe and the Oder, two of the greatest rivers in Germany, take their course from the western sides, the first of the Bohemian and the other of the Moravian mountains, which yet are the steepest. Many originate from lakes, as the Shannon with us; many take such a winding course, that from a bare knowledge of the place of their disemboggement it is impossible to judge from what side of a mountain they issue, if from any; their course at most discovers the depression of the general level of the country.

"In 1798, the celebrated traveller and circumnavigator, John Reinhold Forster, published a geological

tract which merits so much more attention, as all the facts were either observed by himself, or related to him by the immediate observers. In this he states as a fact universally observed, that the south and south-east sides of almost every mountain are steep, but that the north and north-west sides are gently covered and connected with secondary strata, in which organic remains abound, which he illustrates by various instances, some of which have been already, and others will presently be mentioned.

At present this fact attracts the greatest attention, being obviously connected with the original structure of the globe, and clearly proving that mountains are not merely fortuitous eruptions unconnected with transactions on the surface of the earth, as has of late been confidently advanced.

"I shall now state the principal observations relative to this object, that have been made in different parts of the world.

In Europe.

1. The mountains that separate Sweden from Norway extend from north to south, their western sides are steep, and the eastern gentle. 1. Berg. Erde Beschreib. p. 157.

2. The Carpathian mountains run from east to west; their southern sides towards Hungary are steep, their northern towards Poland moderate. Foster, § 46.

3. Dr Walker, professor of natural history at Edinburgh, observed that the coasts and hills of Scotland are steeper and higher on the western side than on the eastern. Jamieson's Mineralogy of Scotland, p. 3. However, Jamieson observed, that the south side of the Isle of Arran is the lowest, and the north side the highest, p. 51.

4. The mountains of Wales are gentle on the eastern and steep on the western sides.

5. The mountains of Parthery, in the county of Mayo, are steep on the western side.

6. The mountains which separate Saxony from Bohemia, descend gently on the Saxon or northern side, but are steep on the Bohemian or southern side. Charpentier, p. 75. The southern declivity is to the north as six to two. 2. Bergm. Journ. 1792, p. 384, and 385.

7. The mountains which separate Silesia from Bohemia run nearly from east to west, yet are steeper on the northern or Silesian side than on the opposite Bohemian. Affemann's Silesia, 335. Such branches as run from north-east to south-west, have their western covered with primordial strata, and consequently less steep. 4. New Ros. p. 157.

8. The Meissener in Hesse is steeper on the north and east sides, which face the Warre, than on the south and western. 1. Bergm. Journ. 1789, p. 272.

9. The mountains of the Hartz and Habichtswald are steep on the south, and gentle on the northern sides. Foster, § 46.

10. The Pyrenees, which run from east to west, are steeper on the southern or Spanish side. Carbonieres, xiii.

11. The mountains of Crim Tartary are gentle on the northern, and steep on the southern sides. Foster, ibid.

12. The Oural, which stretch from north to south, are far steeper on the western than on the southern sides. Herman Geologie, p. 90; and, 2. Ural Beschreib., p. 389.

13. The mountain of Armenia, to the west of the Oural, is steep on its east and north sides; but gentle on the southern and western. 1. Pallas Voy. p. 277.

14. The Altaishan mountains are steep on their southern and western sides, but gentle on the northern and eastern. Foster, ibid. and Herman. 2. Ural Beschreib., p. 390. in the note.

15. So also are the mountains of Caucasus. 3. Schriftl. Berl. Gelasch. 471.

16. The mountains of Kamtschatka are steep on the eastern sides. Pallas, 1. As. Petropol. 1777. p. 43.

17. The Ghauts in the Indian peninsula are steep on the western side.

18. The mountains of Syria, which run from north to south, skirting the Mediterranean, are said to be steeper on the western side, facing the Mediterranean. 4. La Metherie, p. 380.

“The Cordilleras run from north to south; their western flanks towards the Pacific are steep, their eastern descend gradually.

“In Guiana there is a chain of mountains that run from east to west; their southern flanks are steep, their northern gentle. Voyages de Condamine, p. 140.” *

The theory according to which Dr Kirwan attempts to explain the appearances of mountains which are enumerated above, will be given in the next chapter.

We have already, under the article BAROMETER, No 44. shewn the method of computing the height of mountains by means of that instrument. The following table shews the height of the principal mountains in the globe, chiefly according to this computation.

In this table the second column shews the height as estimated by the barometer, and the third the same by geometrical calculation. Where the numbers are placed in the middle of these two spaces, it denotes an uncertainty by what method the computation has been made.

The course of mountains is that direction of their length in which they descend and grow lower; or if a river runs parallel to them, they are said to have their course in the direction of the stream of the river. The course of mountains is seldom uniform. It has been laid down as a general maxim by Buffon, that when there are two parallel chains of mountains, the salient angle of one of the chains always corresponds with the internal angle of the other; but later geologists have ascertained that this circumstance does not generally hold, except when a river runs between the two chains.

It generally happens, that one particular mountain, or chain of mountains, is composed of those stony materials which we have denominated primitive; while the rest is made up of the secondary compounds. The primitive substances occupy the base and central parts of the mountain, and often extend to its very summit: the secondary cover these, and are generally found on the flanks or sides of the mountain, though sometimes they cover the top of the mountain. In a chain of mountains there are commonly three, and often five parallel ridges, of which the central ridge is composed of primitive compounds, and those on each side of it, chiefly or entirely of secondary compounds. Hence mountains are usually divided into primary or primeval, and secondary or epizootic; the latter term being given to the secondary mountains from their being replete with shells and other remains of animal beings. The secondary mountains are also sometimes divided into original and derivative, for a reason that will appear hereafter.

The primary mountains, besides their being in the centre, and destitute, or nearly so, of organic remains, may generally be distinguished by the ruggedness and angular appearances arising from the different nature and hardness of the substances of which they are composed; the quartz and harder granite resisting the attacks of the air and weather, while the other substances being softer, gradually decay, and leave the harder in the form of spires and angles. Where, however, the primitive compounds have been completely covered with secondary strata, these angular appearances seldom take place; and the mountain is only to be distinguished by its position and the structure of its internal parts. The secondary mountains generally have their tops

rounded, and much smoother than those of the primary mountains.

In some cases a number of mountains appear united at their tops into an extensive plain or platform, from which they seem to diverge and branch in every direction. The most remarkable instance of this kind occurs in Tibet. (See GEOGRAPHY, N^o 41.)

It is difficult to acquire a knowledge of the interior structure of mountains. The greater part of them is hid from our view, and nature only exposes them in a few points by means of fissures, caverns, and intermediate valleys.

The materials of which mountains consist are disposed either in irregular heaps, or piles variously intersected by rifts, or in beds or strata separated from each other by rifts, often horizontal, or varying from that direction by an angle of from 5 to 40 degrees, and sometimes much more considerably, approaching even to a vertical position. The strata of mountains are most frequently in the direction of their declivity, yet sometimes their course is directly opposite, or countercurrent: the best manner of determining the angles of their course is by discovering that of their rifts. It chiefly depends on the unevenness of the fundamental ground that supports them. According to Saussure, most of the elevated granitic mountains in Switzerland are formed of immense vertical pyramidal laminae, parallel to each other, that is, piles somewhat inclining from the unequal distribution of their weight, a disposition that may well be expected from collateral crystallizations; but this disposition is not universal, for they have been found in Saxony, and in the Pyrenees, horizontally stratified; much less can it be said, that this vertical position is general, for the strata of gneiss are generally horizontal, and commonly very regular, discovering no traces of a violent shock. Mount Rosa, next to Mount Blanc, the highest in Europe, consists also of gneiss, which M. Saussure found horizontally stratified.

Shangin, who lately (1786) travelled over the Altaïchan mountains, being consulted by Pallas, whether he had found any vertical layers or strata therein, answered, he had not; but that he found them perfectly horizontal on the banks of the river Tschary.

Mountains of primitive limestone are frequently in irregular piles, but often also horizontally stratified. Siliceous schistus is also often horizontally stratified.

Many argillites, particularly roof slates, are generally said to have nearly a vertical position: but Voight has shewn that it is only their lamellæ that are so situated; their horizontal seams, and their walls, discovering their true position; their verticality arising only from the drain of the water, and, consequently, their contraction in that direction: hence those that are most silicified, as they contract less, discover less verticality. Sometimes horizontal strata overlap on both sides. Sometimes they are flanked on both sides with vertical strata.

"Much confusion prevails in the structure of the Pyrenees, and of the Grison mountains, and those on the borders of the Baikal, and other great lakes.

"The perturbed state of the strata often proceeds from the decomposition of internal beds of pyrites, to which water has had access; this appears to be the cause of the alterations observed in the mountain of Rabenberg, on the frontiers of Saxony. In this mountain a double direction of the strata of gneiss is observed; between both the strata are vertical, and a large intermediate space is filled with iron ore: but this mountain contains beds of pyrites and vast swallows; most probably then the pyrites swell, uplifted the whole, and the dissolved iron flowed into the vacancy, from which the water afterwards drained off on the sides.

"In secondary mountains, particularly the calcareous, the greatest disorder often prevails, though in general their stratification is horizontal.

"The calcareous mountains of Savoy are often arched like a lambda, probably from the sinking of the intermediate strata, the intermediate remaining horizontal. Sometimes they assume the form of the letters Z, S, C, or of a disjointed OC, the convexities facing each other. So also in the Pyrenees, they sometimes overlap, from an unequal distribution in their original formation, and bend various ways. They assume a spiral form, or that of a horse-shoe placed horizontally.

"According to Lehman, most secondary strata present hollows or moulds, (as they are called,) from internal depression. But sometimes also elevations, from an original elevation in the fundamental stone.

"In Scotland, all the secondary strata in the vicinity of primeval mountains, are nearly vertical; but at a greater distance they approach more to an horizontal direction."

We shall now trace the course of the principal mountainous chains on the globe, and in accompanying us, the reader may have before him a good map of the world.

M. Buache places the most elevated points of the great chains of mountains under the equatorial line: but, according to Pallas, the fullest and most continuous lands, and perhaps likewise the most elevated, are to be found at a distance from the equator, and towards the temperate zones. If, in fact, we survey the globe's surface, we shall not be able to perceive that chain of mountains, which running from east to west, and dividing the earth into two portions, ought again to meet. On the contrary, extensive plains seem to accompany the line through almost its whole extent. In Africa, the deserts of Nigritia and those of Upper Ethiopia, are on the one side of the line; and on the other are the

fandy plains of Nicoco, Caffraria, Monemugi, and Zanguebar. From the eastern shores of Africa to the Sunda islands, is a space of 1500 leagues of sea with almost no islands, except the Laccadive and Maldivic islands; most part of which have little elevation, and which run from north to south. From the Molucca islands and New Guinea, to the western borders of America, the sea occupies a space of 3000 leagues. Though Chimborazo and Pichincha in America, the two highest mountains which have been measured, are near and even under the line, yet from this no conclusion can be drawn; because on one side these mountains run in a direction not parallel to the equator; the Andes or Cordilleras attain a greater elevation as they remove from the equator towards the poles; and a vast plain is found exactly under the line, between the Oronoko and the river of the Amazons. Besides, the latter river, which takes its rise in the province of Lima about the 11th degree of south latitude, after crossing the whole of South America from west to east, falls into the ocean exactly under the equator. This shows that there is a descent for the space of 12 degrees or 300 leagues. From the mouth of the river of the Amazons, to the western shores of Africa, the sea forms another plain of more than 50 degrees.

From the few certain facts and accurate observations which we have received from well informed travellers, we might almost affirm that the most elevated land on our globe is situated without the tropics in the northern and southern hemispheres. By examining the course of the great rivers, we in fact find that they are in general discharged into three great reservoirs, the one under the line, and the other two towards the poles. This, however, we do not mean to lay down as universally true; for it is allowed, that, besides the two elevated belts, the whole surface of the earth is covered with innumerable mountains, either detached from one another or in a continued chain. In America, the Oronoko and the river of the Amazons run towards the line, while the river St Lawrence runs towards the 50th degree of north latitude, and the river de la Plata towards the 40th degree of south latitude. We are still too little acquainted with Africa, which is almost all contained within the tropics, to form any accurate conclusions concerning this subject. Europe and Asia, which form only one great mass, appear to be divided by a more elevated belt, which extends from the most westerly shores of France to the most easterly of China, and to the island of Sagaleen or Anga-hata, following pretty nearly the 50th degree of north latitude. In the new continent, therefore, we may consider that chain where the Missisippi, the river St Lawrence, the Ohio, and the river de los Estrechos, take their rise, as the most elevated situation in North America; whence the Missisippi flows towards the equator, the river St Lawrence towards the north-east, and the rest towards the north-west. In the old continent, the belt formerly mentioned, and to which we may assign about 10 degrees of breadth, may be reckoned from the 45th to the 55th degree of north latitude: for in Europe the Tagus, the Danube, the Dnieper, the Don, and the Volga, and in Asia the Indus, the Ganges, the Meran, the Micon, the Hoang-ho, and the Yang-tse-Kiang, descending as it were from this elevation, fall into the great reservoir between the tropics; whilst towards the north

north the Rhine, the Elbe, the Oder, the Vistula, the Oby, the Jenisei, the Lena, the Indigirka, and the Kowyma, are discharged into the northern reservoir.

Judging from those mountains the height of which has been calculated, and from the immense chains with which we are acquainted, we may infer that the highest mountains are to be found in this elevated belt. The Alps of Switzerland and Savoy extend through the 45th, the 46th, and the 47th degrees. Among them we find St Gothard, Furca, Bruning, Rufs, Whiggis, Scheidek, Gunggels, Galanda; and lailly, that branch of the Swiss Alps which reaches Tirol by the name of Arlenberg and Arula. In Savoy, we meet with Mont Blanc, the Peak of Argentiere, Cornero, Great and Little St Bernard, Great and Little Cenis, Coupeline, Servin, and that branch of the Savoyard Alps which proceeds towards Italy through the duchy of Aost and Montferrat. In this vast heap of elevated peaks, Mount Blanc and St Gothard are particularly distinguished. The Alps, leaving Switzerland and Savoy, and passing through Tirol and Carniola, traverse Saltzbourg, Stiria, and Austria, and extend their branches through Moravia and Bohemia, as far as Poland and Prussia. Between the 47th and 48th degrees, we meet with Grimming the highest mountain of Stiria, and Priel which is the highest in Austria. Between the 46th and 47th degrees, the Bacher and the Reinschnicken, form two remarkable chains. The upper one, which traverses the counties of Trenchin, Arrava, Scepus, and the Kreyna, separates Upper Hungary from Silesia, Little Poland, and Red Russia; the inferior one traverses Upper Croatia, Bosnia, Servia, and Transylvania, separates Lower Hungary from Turkey in Europe, and meets the upper chain behind Moldavia, on the confines of Little Tartary. In these mountains are situated the rich mines of Schemnitz.

To form a general idea of the great height of this Alpine belt, it is necessary only to remark, that the greatest depth of the wells at Schemnitz is 200 toises; and yet it appears, from the barometrical calculations of the learned M. Noda, that the greatest depth of these mines is 286 toises higher than the city of Vienna. The granito-argillous mountains of Schemnitz, and of the whole of this metallic district, are inferior, however, to the Carpathian mountains. Mount Krivany in the county of Arrava, and the Carpathian mountains between Red Russia and the Kreyna, appear by their great elevation to rule over the whole of the upper Alpine chain. In the inferior chain we likewise meet with mountains of an extraordinary height; among others, Mount Mediednik, which gives its name to a chain extending far into Bosnia; and Mount Hemus, celebrated even among the ancients. In short, this extensive chain reaches into Asia, and is there confounded with another chain no less famous, which, following exactly the 50th degree of latitude, runs through the whole of Asia. This chain of mountains is described by Dr Pallas in the work above mentioned; and we shall now trace its course in company with this intelligent observer.

This author places the head of the mountains of Oural, between the sources of the Yaik and the Bialia, about the 53d degree of latitude, and the 47th of

longitude. Here the European Alps, after having traversed Europe, and sent off various branches which we shall afterwards examine, lose their name, which is changed into that of the Ouralic or Uralian mountains, and begin their course in Asia. This lofty chain, which separates Great Bulgaria from the deserts of Ichimika, proceeds through the country of the Eleuths, follows the course of the river Irtysh, approaches the lake Telekskaia, and afterwards forms a part of the same system of mountains with the Altaic chain. There they give rise to the Oby, the Irtysh, and the Jenisei, which begin their course about the 50th degree of north latitude, and fall into the Frozen ocean.

The Altaic chain, after having embraced and united all the rivers which supply the Jenisei, is continued under the name of Saianer, without the smallest interruption, as far as the Baikal lake. The extension of this chain to the south forms that immense and elevated plain which is lost in Chinese Tartary, which may be compared with the only plain in Quito, and which is called Gobi or Chamo. The Altai afterwards interposing between the source of the Tchikoi and of the rivers which supply the Amur or Sagaleen, rises towards the Lena, approaches the city Jakuck beyond the 60th degree of latitude, runs from that to the sea of Kamtschatka, turns round the Ochotkoi and Penfink gulfs, joins the great marine chain of the Kurile isles near Japan, and forms the steep shores of Kamtschatka, between the 55th and 60th degrees of latitude. After running in the same parallel, and giving rise to the Ohio, the Riviere Longue, the river St Lawrence, and the Missilippi, they are lost in Canada. From the eastern shores of America to the western shores of Europe, we find a vast interruption.

The European Alps produce three principal chains, which run towards the equator, and some smaller ones running towards the pole. The first southern chain is sent out through Dauphine; traverses Vivarais, Lyonnais, Auvergne, Cevennes, and Languedoc; and, after joining the Pyrenees, enters Spain. There it divides into two or three ramifications, one of which runs through Navarre, Biscay, Arragon, Castile, Marche, and Sierra Morena, and extends into Portugal. The other, after traversing Andalusia and the kingdom of Granada, and there forming a number of mountains, again makes its appearance, beyond the straits of Gibraltar, in Africa, and coasts along its northern shores under the name of Mount Atlas. The second principal chain of the Alps passes out through Savoy and Piedmont; spreads its roughness over the states of Genoa and Parma; forms the belt of the Apennines; and after frequently changing its name, and dividing Italy into two parts, terminates in the kingdom of Naples and in Sicily, producing volcanoes in every part of its course. The third chain is sent off from Hungary, and scatters innumerable mountains over all Turkey in Europe, as far as the Morea and the Archipelago at the bottom of the Mediterranean sea. The northern branches, though smaller at first, are no less clearly defined; and some of them even extend their ramifications as far as the Frozen ocean. An Alpine branch, issuing from Savoy through the country of Gex, proceeds through Franche Comte, Sautgaw, Alface, the Palatinate, and Veterabia.—

Another issue from the territory of Salzbourg, passes along Bohemia, enters Poland, sends off a ramification into Prussia towards the deserts of Waldow, and after having passed through Russia is lost in the government of Archangel.

The Asiatic Alps send forth in like manner several branches both to the south and north. The Ouralic mountains, between the sources of the Bielaia and the Jaik, produce three principal branches; the first of which, including the Caspian sea in one of its divisions, enters Circassia through the government of Astracan, passes through Georgia under the name of Gaucaus, sends a vast number of ramifications to the west into Asiatic Turkey, and there produces the mountains Tschinder, Ararat, Taurus, Argée, and many others in the three Arabias; while the other division, passing between the Caspian sea and the lake Aral, penetrates through Chorasan into Persia. The second branch, taking a more easterly direction, leaves the country of the Eleuths; reaches Little Bucharia; and forms the ramparts of Gog and Magog, and the celebrated mountains formerly known by the name of Cas, which M. Bailly has made the seat of the war between the Dives and the Peris*. It traverses the kingdoms of Casgar and Turkestan, enters through that of Lahor into the Mogul territory, and, after giving rise to the elevated desert of Chamo, forms the western peninsula of India. While these two branches run towards the south, the third branch of the Ouralic chain rises towards the north, following almost the 79th degree of longitude, and forms a natural boundary between Europe and Asia; without, however, bounding the immense empire of Russia. This chain, after coming opposite to Nova Zembla, divides into two considerable branches. The one, running to the north-east, passes along the Arctic shores; the other, proceeding towards the north-west, meets the northern European chain, traverses Scandinavia in the shape of a horseshoe, covers the low lands of Finland with rocks; and, as is observed by Dr Pallas, appears to be continued from the North Cape of Norway through the marine chain of Spitzbergen, scattering islands and shelves perhaps throughout the northern ocean, that, passing through the pole, it may join the northern and eastern points of Asia and North America.

The Ouralic, which in the country of the Mongols becomes the Altaic chain, proceeds towards the equator. After forming the mountains and caverns wherein, as we are told, the ashes of the Mongol emperors of the race of Gengis-Kan are deposited, together with the vast plain of Chamo, consisting of arid sand, and the frightful rocks and precipices of Thibet, which form the mysterious and desert retreats of the Grand Lama, it crosses the rivers Ava and Menan; contains in its subdivisions the kingdoms of Ava, Pegu, Laos, Tonquin, Cochinchina, and Siam; supports the peninsula of Malacca; and overspreads the Indian ocean with the isles of Sunda, the Moluccas, and the Philippines. From the borders of the Baikal lake and of the province of Selinginskoy, a branch is detached, which spreads over Chinese Tartary and China, is continued into Corea, and gives rise to the islands of Japan.

The great chain having extended to the north, near the city of Jakuck, upon the banks of the Lena, sends

off one of its branches to the north-west, which passing between the two Tungusta, is lost in marshy grounds lying in the northern parts of the province of Jenniseiskoy. The same chain, after it has reached the eastern part of Asia, is lost in the icy regions of the north about Nos-Tschalatskoy, or the Icy Promontory, and Cape Czuczenkoy.

It will be more difficult, perhaps, to trace the elevated belt in the southern hemisphere beyond the tropic of Capricorn, than it has been to distinguish that towards the north. An immense extent of ocean seems to occupy the whole Antarctic part of the globe.—The greatest south latitude of the old continent is not more than 34 degrees, and South America scarcely extends to the 55th degree. In vain has the enterprising Cook attempted to discover regions towards the pole: his progress was constantly interrupted by tremendous mountains and fields of ice. Beyond the 50th degree no land and no habitations are to be found. The islands of New Zealand are the farthest land in these desert seas; and yet the south cape of Taral-Poenamoo extends only to the 48th degree: We do not mention Sandwich-land, which is situated in the 38th degree, because it is too small and too low. It must be recollected, however, that according to the declarations of travellers, the Cordilleras become higher as they advance southward to the Straits of Magellan; and that Terra del Fuego, which lies in the latitude of 55, is nothing but a mass of rocks of prodigious elevation. America, however, exhibits to our view elevated points, whence chains of mountains are distributed in different directions over the whole surface of the new continent. There must likewise be great reservoirs, where the most remarkable rivers take their rise, and from which they necessarily descend towards their mouths. In the southern hemisphere, this elevated belt is nearer the equator; and though it does not extend to the 50th degree, it is evidently to be met with, and may be accurately traced, between the 20th and 30th degrees. The high mountains of Tucuman and of Paraguay, which intersect South America about the 25th degree of latitude, may be considered as the American Alps. If we look into the map of the world, we shall be able to distinguish an elevated belt all along this parallel. In Africa, Monomotapa and Caffraria are covered with very high mountains, from which pretty large rivers descend. In the Pacific ocean, we find New Holland, New Caledonia, the New Hebrides, and the Friendly and the Society islands, under the same parallel. We may, therefore, with sufficient propriety, distinguish this parallel by the name of the Southern Alps, as we have already distinguished the elevated belt of the 50th degree of north latitude by that of the Northern Alps. In America, the Rio de la Plata, which after a course of 500 leagues falls into the ocean at the 35th degree of south latitude; the Pavana, which rises from the mountains of the Arapés, and falls into the Plata at Corrientes; the great number of rivers which flow into that of the Amazons, such as the Parana, which receives in its course the tribute of more than 30 other rivers; the Madera, the Cuchirara, the Ucayal, &c. &c. all descend from these southern Alps. From these Alps likewise three considerable branches of mountains are detached, which

go by the common name of Andes or Cordilleras.—The first branch, which extends towards the south, and passes out from Paraguay through Tucuman, separates Chili from these provinces and from Chimito, and is continued through Terra Magellanica as far as Terra del Fuego. The second branch, directing its course towards the equator, traverses Peru, in vain endeavouring to conceal treasures which the avarice of men has taught them to discover in its bowels; bounds the Spanish Missions; enters Terra Firma through Popayan; and unites South and North America by the isthmus of Panama. The third division, issuing from Paraguay through Guayra and the territory of Saint Vincent, traverses Brazil, distributes ramifications into Portuguese, French, and Dutch Guiana, crosses the Oroonoko, forms the mountains of Venezuela, and near Carthagea meets the second branch coming from Popayan.

We have already supposed, that the elevated belt of North America was situated about the 45th degree of north latitude; and there we imagined we recognized the continuation of the northern Alps of the old continent. This chain likewise sends forth considerable branches on both sides. One of them is detached across the sources of the Mississippi, the Belle Riviere, and the Missouri, and at the entrance of New Mexico divides, in order to form California to the west, and the Apalachian mountains to the east.—Thence proceeding through New Biscay, the audience of Guadalupe, Old Mexico, and Guatemala, it meets at Panama the southern branch, which is part of the Alps of Paraguay. The second branch, following the course of the Mississippi, separates Louisiana from Virginia; serves as a bulwark to the United States of America; forms the Apalachian mountains in Carolina; and at last, traversing East Florida, encloses the gulf of Mexico with the Great and Little Antilles. In the north, we can trace the branches of the elevated belt; on one side observe them proceeding towards Canada, directing their course through Labrador to Hudson's Straits, and at length confounded with the rocks of Greenland, which are covered with eternal snow and ice. On the other side, we see them rising through the country of the Assiniboines and the Kiskinios, as far as Michinipis and the northern Archipelago.

In tracing the course and direction of the British mountains, we shall begin with the central chain, which runs through the southern part of the island from north to south, commencing at Gelsdale, about 14 miles to the south-east of Carlisle, and ending at Land's End in Cornwall, or rather in the Scilly isles to the west of this. This chain passes from Gelsdale forest through the western districts of Durham and Yorkshire, forming the hills called Kelton Fell, Stanmore, Widdell Fell, Wildbore Fell, Bow Fell, Home Fell, Bun Hill, &c. A little to the west of the chain stand several detached mountains, the principal of which is Skiddaw in Cumberland. Passing through Yorkshire we find Craven, Whernside, Ingleborough, and Pennygent; and on the east of Lancaster is Pendle. In this course there are several miles of coal and lead. The chain next proceeds through Derbyshire, and in this part of the ridge a great variety of valuable minerals are found, especially lead, copper, gypsum, fluor, barytic earth, mar-

tial pyrites, iron ore, manganese, and several ores of zinc. About this point the ridge stretches a little into Cheshire, and seems to terminate; a central chain of somewhat less elevation may, however, still be traced, proceeding in a wavy direction towards Salisbury, and having three irregular branches, two to the east, and another running to the south-west into Cornwall. The first eastern branch proceeds towards Norfolk, and to this belong some considerable hills, especially those of Gog Magog in Cambridgeshire. The second branch passes into Kent, and diverges a little into Surrey and Hampshire. The continuation of this chain is afforded by the hills of Mendip, Polden, Ledgemoor, and Blackdown in Somersetshire; the Tores and Wilds of Dartmore in Devonshire; and the upland Downs of Cornwall. Malvern hills in Worcestershire deviate a little from the chain, but those of Cotswold in Gloucestershire appear to be a continuation of it. The principal mineral found in this ridge of mountains, after leaving Derbyshire, is the tin ore of Cornwall.

Wales contains many mountains, especially in its northern part, where Snowden is celebrated for its height and classical fame. The top of this mountain is formed almost into a point, and commands an extensive view, not only of the neighbouring counties, but of part of Scotland and Ireland, and the isles of Mann and Anglesey. A line of mountains proceeds from Snowden along the western coast to Plinlimmon; and in this line lie Urron Seth, Caeridris, and Moyle Vadian. A few hills of little elevation proved towards Shropshire, among which the Wrekin is the most remarkable. Another small chain proceeds south towards Cardiff, but contains no hills of any eminence.

Leaving England, and proceeding towards the north, we find the Cheviot Hills, so celebrated in the history of the border skirmishes. These form a regular ridge, running from south-west to north-east, where they join the hills of Galloway. In this part of Scotland there are several mountainous ridges running in various directions, generally north and south according to the course of the rivers; but there is, properly speaking, no uniform chain. Dumfriesshire contains several mountains, some of which are of a considerable height, especially Hartfell in Annandale, from which proceeds the celebrated chalybeate spaw; Lowther near Leadhills; Blacklaw on the borders of Ayrshire; Erick Pen, in Eskdale moor; Carnkinnow near Drumlanrigg; and Queensberry hill, which gives the title to the dukedom of that name. Proceeding towards the north, we find Pentland hills, a little to the south-west of Edinburgh, and the romantic hills of Arthur's seat and Salisbury Craig, in the immediate vicinity of that city. On the eastern coast, before crossing the Firth, is North Berwick Law, which must be considered as closing the list of southern hills in Scotland. The principal part of these southern hills consists of calcareous earth, and argillaceous schistus; and except in those of Galloway, granite and other primitive rocks are very sparing. In the Lothian hills the calcareous strata are surmounted by vast blocks of trap, wacke, and basalt.

On the north of the Firth are the hills of Ochil, of little elevation, but celebrated for affording large quantities of agates and chalcidones. The hills of Kinneoul and Dunfinnan in the eastern part of Perthshire, are generally considered the last of the lowland hills.

The principal northern chain of British mountains is that of the Grampian hills, extending from Loch Lomond to Stonehaven, and forming the southern boundary of the Highlands; and rising by a gradual transition from the Sidlaw hills on the east, the Campsie hills on the west, and the Ochils in the middle. The principal mountains of this chain are Ben Lawers, Ben More, Schiehallion, Ben Vorlich, Ben Lomond, and Ben Leddy. Near Ben Lawers is Ben Nevis, the highest mountain in Britain, and to the north-west of this near Fort Augustus, is the long hill of Corri Allok. About 30 miles to the east of this is the high mountain of Cairngorum, famous for the specimens of quartzose fiones found there. Numerous mountains lie in the second divisions of the Highlands, beyond Loch Linnè, and Loch Ness, especially on the western shore, which is crowded with hills. Few of these are considerable. To the west of Ross-shire are several hills, among which Ben Chat, Ben Chaske, and Ben Golich are the most remarkable. More inland stands the high mountain of Ben Wevis, nearly equal to Ben Nevis. In most of these mountains the primitive rocks prevail, and granite is often very abundant. Few minerals, however, except iron ore, are found.

Ireland contains but few mountains, and none of any considerable importance. They generally form short lines, or appear in detached groups, one of the highest of which is that on the west and south of the lake of Killarney, in which is the mountain of Mangerton. A small line of hills called Sheekey mountains runs on the north-west of Bantry Bay, passing towards the east. To the northward of this stands Sliblogher and Nagles, and towards the east are the hills of Knockemdown. In the county of Leinster is a mountain of the same name, and to the south of Dublin are the Wicklow hills, from which there were lately such great expectations of golden treasure. In Ulster stand the mountains of Mourne, the highest of which, Donard, is said to be nearly the height of Mangerton. The most mountainous part of Ireland is the western peninsula of that island, towards which, in the county of Mayo, stands Nephin, one of the highest in the kingdom. On the south-east of Clewbay is the mountain of Croagh Patrick, also in the county of Mayo, which is the last Irish hill of any importance.

We cannot here with propriety enter on the theory of the formation of mountains. The hypothesis of the principal geological writers with respect to this subject, will be seen from the general view of the theories to be given in the next chapter. We may in this place only remark, that all the systems which have been constructed, to explain the formation of the primitive mountains, with respect to which there is the most dispute, may be reduced to three.

In the first of these, mountains are supposed to have been formed such as we now see them, except that they have suffered some degradations and modifications, from certain accidents posterior to their original formation, and that these mountains owed their elevation above the places which surround them, to one single accidental accumulation of more materials in one place than in another; an accumulation which might have taken place without that great precipitation which preceded and occasioned the consolidation of the crust of our globe.

In the second hypothesis, all the primitive mountains

are supposed to have been raised by one cause, and in one certain manner; and the materials which compose them, to have been thrown out of their natural position. It is with respect to this raising or displacement that geologists have imagined so many different hypotheses.

In the third general theory, these mountains are supposed to have become pre-eminent from the accidental lowering or removal of the materials which originally surrounded them, whether this happened from the materials composing these mountainous situations having suffered no displacement, or that they had been themselves removed.

M. Dolomieu is of opinion, that there are mountains whose situation and structure favour each of these three hypotheses.*

We have described dykes (No. 15.) to be those interruptions of the strata which are formed by perpendicular fissures filled with stony substances. As these stony matters are frequently of that kind called whin-stone, these dykes are commonly called whin dykes, and the history of these is very important, as they form one of the principal subjects in the principal theories of the earth.

Dykes have received different denominations, descriptive, in some measure, of the nature of the substances of which they are composed; or of the seeming effects they have produced on the intersected horizontal strata. They are called basaltic veins, trap dykes, whin dykes; and in the coal countries of Scotland they are called gaws, from the idea that they have occasioned the separation of the coal, and contiguous strata, through which they run.

These dykes have been more attentively observed in coal countries, than where they occur elsewhere; because on the accurate knowledge of their course, inclination and thickness, depend, in a great measure, the judicious and successful operations of the miner, when his workings approach the dike, or render it necessary to cut through it to reach the strata of coal on the other side. But, though less attended to, they have been observed and traced in other places, where a great extent of the horizontal strata have been exposed in the beds of rivers, as in the bed of the Water of Leith, above St Bernard's Well, near Edinburgh, and on the sea shore, especially on the western coasts of Scotland, where the rocks are more abrupt and precipitous, and where the violence of the Atlantic ocean has removed part of the horizontal strata, and left the vertical strata remaining, like immense walls or dykes. Hence probably the origin of the name; and as they often consist of that species of stone called whin-stone, this epithet has been added.

The course, however, of the greater number which we have had the opportunity of examining, generally lies between the points of the compass S. and S. E. and N. and N. W. This is most frequently the course of the whin dykes of Illay and Jura; it is the course of a remarkable dyke which traverses the coal strata at the village of Stevenston, near Saltcoats, in Ayrshire; part of which is seen on the surface, not many hundred yards to the north of the west end of that village;

General Distribution of the Materials of the Earth.

lage; and it is the course of two dykes, still more remarkable, in the island of Great Cumbry, in the fifth of Clyde.

Geologists, who have treated this subject, do not seem to have marked, with much attention, the course of the dykes. They have mentioned in general terms, that they follow all directions. More extensive observation may probably shew, that the most frequent directions of the principal dykes, is from north to south, or a few points deviation from that course. And if this be established, by a fuller and more accurate history of dykes, the analogy between them and metallic veins will be more complete; for it is observed of the latter, that the most powerful, that is, the most productive, run from north to south.

Dykes do not always run in a straight line. In their course they form certain flexuosities. But, in this winding course, the deviations are usually so small, as to have little effect on the general direction of the dyke, which, upon the whole, may be considered as nearly the same.

The continuity of dykes is sometimes interrupted, exactly in the same manner as frequently happens to the horizontal strata, and which, in technical language is termed a slip.

In the island of Ilay we have observed two dykes of this description, the one on the south side of Lochindal, near the point of Laggan; the other on the shore of the south-east part of the island, a little to the south of the house of Ardmore. In both these dykes, the extent of the separation of the slip was just equal to the thickness of the dyke. The opposite sides were brought exactly into the same line.

After this separation, these dykes, in so far as they could be traced, preserve the same thickness, course, and inclination as formerly.

A very remarkable dyke has been discovered in the coal field, in the district of Boulogne in France. It runs in the form of a crescent from north to west.

The direction of dykes downwards is seldom perpendicular. This deviation from a line perpendicular to the horizon is called their inclination. The inclination of a dyke is usually denominated the hade or hading. See the article COALERY.

The inclination of different dykes, and even of the same dyke, is various, sometimes approaching to, and sometimes deviating from the perpendicular. The extent of dykes downwards, we believe, has not been ascertained with any degree of accuracy, and the termination of very few has yet been detected. The depth to which researches of this kind can be carried, is comparatively small. With all the ardour, ingenuity, and power of man, investigations to determine this point, will probably always be limited by the extent of his mining operations. The crescent-formed dyke just mentioned, which occurs in a coal-field in the district of Boulogne in France, which consists of a species of marble, found in several quarries in the vicinity, has been traced to the perpendicular depth of 600 feet, where it is succeeded by a schistus rock, which latter, with the same course and inclination, continues to intersect the horizontal strata.

The extent of dykes in length has not been accurately determined. Indeed, it must be extremely difficult to trace them with any degree of certainty. For

those which are observed on the sea coast, where they are most conspicuous, soon disappear in the mountains, on the one hand, or on the other lose themselves in the sea. And, as the extent of the same coal field rarely exceeds a few miles, they have seldom been followed beyond its limits. In many cases, the change in the nature and arrangement of the strata, renders it almost impossible. Some, however, have been traced to a very great extent; one in particular, on the banks of the river Meuse in the Netherlands, has been followed in its direct course, to the distance of four leagues; and of this dyke it is observed, if pursued through all its windings, the extent is not less than six leagues.

The thickness of dykes is various. Sometimes they are observed no thicker than a few inches. From that they increase to one foot, six feet, and very often are found from 10 to 20 feet. There is one in the island of Ilay, of the enormous thickness of 69 feet. This immense dyke accompanies a lead vein, about a foot thick, which is included between it and the limestone strata. In this mining field, two whin dykes, one of them 10 feet thick, have been discovered, crossing the metallic veins.

In going downwards, dykes are said to decrease in thickness. This is particularly observed of dykes of smaller magnitude. Of smaller dykes it is also said, that they diminish in thickness towards the extremities.

In one respect, some whin dykes are exactly analogous to metallic veins, in having branches, or in the miners phrase, strings going off and traversing the contiguous strata, and forming in the course they take, an acute angle with the principal dyke. A whin dyke of this description has been observed in the island of Jura, on the shore of the found. The diverging branch terminated in a point among the horizontal strata, at the distance of a few feet from the great dyke, assuming altogether a wedge-like form.

If we include metallic veins in the account, the vertical strata may be said to be composed of every kind of mineral substance, but almost always different from the intersected horizontal strata. By this last circumstance their occurrence is at once recognized. In general, the dykes that are found in Scotland, whether in the coal countries, or in the western coasts and islands, where they are so frequent, are of that species of stone which comes under the denomination of trap or whinstone. Dykes, consisting of other species of stone, have also been found in Scotland. On the Mull of Kinmouth, which forms the southern headland, at the entrance of Lochindal, in Ilay, we observed a small dyke of granite, crossing the headland, which is of granular quartz. There are some vertical strata of granite in the island of Icolmkill, of pitchstone in the island of Arran, and of serpentine at Portsoy in Banffshire.

Bergman, in his Physical Geography, supposes that granite was never found to be a component part of vertical strata. What has been already mentioned proves the contrary. Granite dykes have also been discovered in other places. Beeson has observed dykes of this description on the great road between Limoges and Cahors in France, traversing horizontal strata of argillaceous schistus, a species of stone which has generally been considered of later formation than granite. These dykes, he observes, are from an inch to

fix feet in thickness, and the quartz, felspar, and mica, are of larger size than are usually found in the granite of mountains. Dolomieu has made a similar observation, and considers it as a discriminative character, by which the granite of mountains and that found in vertical strata may be easily distinguished. But this is not always to be admitted as a characteristic mark of distinction. The granite dyke which has been already mentioned, crossing the granular quartz, on the Mull of Kinmonth in Islay, is small grained, and others of this latter description have been observed in other places.

There is a very singular dyke on the coast of Ayrshire, between Weems bay and Largs, near the house of Kelly. It is about ten feet thick, traverses the horizontal strata, which consist of plumb-pudding rock, whose cement is sandstone of a red colour, from north-east to south-west, and crosses a larger dike of the whinestone of this country, nearly at right angles. This dike is composed of different materials. Part is of the common whinestone, and part of a plumb-pudding rock, cemented by the matter of the dyke; and these alternate with each other, both in the thickness of the dyke, and lengthwise. On one side, there are four feet thick of whinestone; immediately in contact with this there is plumb-pudding stone three feet thick, and so on alternately, across the whole dyke. In tracing the dyke lengthwise across the whole line, there is found a few yards of whinestone, which is succeeded by a few yards of plumb-pudding stone, and this is again succeeded by the whinestone.

But, for the general view which is here proposed, it is not requisite to give a full account of all the mineral substances which enter into the composition of vertical strata, or even a minute enumeration of all the varieties that are found in whin dykes.

One of the most singular circumstances respecting whin dykes, which seems to have been entirely overlooked by geologists, still remains to be considered. This is the peculiar structure or arrangement of the parts of which they are composed. Of this peculiar arrangement it may be observed in general, that it is in all respects the reverse of what takes place in the horizontal strata.

When the dyke is of small magnitude, it is pretty compact in all its parts; but if an attempt be made to break or separate any part of it, the fracture will be found to run most readily in the perpendicular direction. But when the dyke is of more considerable thickness, it usually forms several divisions, marked by perpendicular fissures, and there is often very great variety in the nature and qualities of the several divisions of the same dyke. The exterior division of one side sometimes, and sometimes the exterior division of both sides, are of a softer texture than the intermediate division; and often contain, in great proportion, specks of radiated zeolite and calcareous spar, while the middle divisions, as well as being harder, are also more homogeneous. In other cases, the reverse of this appears. The middle parts of the dyke are the softest and least compact, exhibiting the greatest variety of heterogeneous substances.

Some whin dykes have a great tendency to assume, when broken, the prismatic form. This is the case with many, even of the most compact texture. In others, where the side of the dyke is exposed to view, and minutely examined, fissures may be traced, discovering

the ends of pretty regular prisms. But in some dykes in the island of Jura, the prismatic columns are entirely separated, and lying loose, are four, five, or six-sided, jointed; the perpendicular fissures forming the joints, and in all respects similar to the perpendicular basaltic columns, except being in the horizontal position. In one of the dykes in the island of Jura, the columns are from 12 to 18 inches in diameter. In some others on the sea shore, near the house of Mr Campbell of Jura, and at the harbour of the small isles, in the same island, there are columns of the enormous size of 10 and 12 feet diameter.

A dyke which traverses the basaltic strata of the Giants Causeway in the north of Ireland, exhibits still more remarkably this peculiarity of structure. The smallest masses detached from it assume the columnar form, and most of them are perfectly regular. The fracture invariably runs in the horizontal direction; the columns consequently lie in the same position, are three, four, five, and six-sided, and are generally of small size.

SECT. III. Of Metallic Veins.

THE history of metallic veins, although far from being so full and satisfactory as could be wished, is more complete than that of whin dykes. The latter have excited no farther attention than as objects of curiosity to the geologist, or as singular facts in establishing a theory, and when they come in the way of the operations of the miner, to discover their connexion with the contiguous strata; while the wants and luxuries of man have roused ingenuity and exertion in exploring the former, on account of the precious and useful metals with which they are stored. Thus, the splendour and beauty of some metallic substances, and the utility of others, have made them in all ages be esteemed and valued by mankind; and consequently they have been the constant objects of pursuit and investigation. It is obvious that the beauty and utility of metals, on account of which they are so much valued and sought after, excite greater interest in procuring them; on the one hand, the researches and observations of the philosopher in furnishing the history and general principles, and, on the other, the immediate application of this knowledge, and of these principles, in the practice and operations of the miner.

The history of whin dykes is, in general, quite analogous to metallic veins; but, of the latter, from what has been stated, we can speak with more certainty and precision.

Three different kinds of metallic veins have been described by geological writers; the perpendicular vein, of veins, the pipe vein, and the flat or dilated vein. We shall consider each of these in their order.

1. Of the perpendicular vein.—This kind of metallic vein occurs most frequently. As may be expected, it is various in its course or direction, thickness, and inclination. Metallic veins are found running in every direction; but, in general, the most powerful veins, that is, the most productive, are observed to run from north to south, or at least a few points deviation from that course; and when any deviation happens, it is usually to the east of north, and to the west of south.

The course or direction of a vein is called in technical

cal language its bearing. The extent of a vein in the line of bearing, we believe, rarely exceeds the range of mountains in which it is discovered. This is the case with the principal vein at Leadhills. It is limited to the chain of mountains in which the operations are now carried on; and although the mines of Wanlockhead are not a mile distant, new veins appear with galena or lead ore, of quite a different quality, and all the accompanying minerals, whether forming part of the vein, or found in cavities, are also quite different from the lead ore and other minerals found in the veins at Leadhills.

The inclination of veins is various. Sometimes they are nearly perpendicular; sometimes they deviate considerably from a perpendicular line; sometimes the same vein in its course downward, inclines to one side; sometimes it is perpendicular, and sometimes it inclines to the other side. When the deviation from the perpendicular does not exceed 10°, the vein is still considered as a perpendicular or vertical vein. When a vein is inclined, the two sides which include the metallic substances are in very different positions, and have consequently received from the miners different names. That side which supports the metallic ore, or on which it seems to lean, is called the ledger side, or simply the ledger. The opposite side which covers the ore, or which overhangs it, is denominated the hanging side, or simply the hanger. From the inclination of the vein being varied in its course downwards, it must appear that the same sides, according as the inclination varies, must change their position and denomination. This will perhaps be more intelligible by the section at fig. 5, in which AA represents the vein; BB, CC, DD, EE, the strata intersected by it; 1. the hanger; 2. the ledger; 3. the hanger; and, 4. the ledger.