in literature and in common life, a conversation between two or more persons, and either written or oral.

As the end of speech is conversation, no kind of writing can be more natural than dialogue, which represents this. Accordingly we find it was introduced at a very early period; for there are several instances of it in the Mosaic history. The ancient Greek writers, especially the philosophers, also fell very much into dialogue, as the most convenient and agreeable method of communicating their sentiments and instructions to mankind. And indeed it seems to be attended with very considerable advantages, if well and judiciously managed; for it is capable of rendering the driest subjects entertaining and pleasant, by its variety, and by the different characters of the speakers. Besides, things may be canvassed more minutely, and many lesser matters, which serve to clear up a subject, may be introduced with better grace, by means of questions and answers, objections and replies, than can be conveniently done in a continued discourse. There is likewise a further advantage in this way of writing, that the author is at liberty to choose his speakers; and therefore, as Cicero has well observed, that when we imagine that we have persons of an established reputation for wisdom and knowledge talking together, this circumstance necessarily adds a weight and authority to the discourse, and more closely engages the attention. The subject-matter of dialogue is very extensive; for whatever is a proper argument of discourse, public or private, serious or jocose—whatever is fit for wise and ingenious men to talk upon, either for improvement or diversion—is suitable for a dialogue.

From this general account of the nature of dialogue, it is easy to perceive what kind of style best suits it. Its affinity with epistles shows there ought to be no great difference between them in this respect. Indeed, some have been of opinion that it ought rather to sink below the style of an epistle, because dialogues should in all respects represent the freedom of conversation, whereas epistles ought sometimes to be composed with care and accuracy, especially when written to superiors. But there seems to be little weight in this argument, since the design of an epistle is to say the same things, and in the same manner, as the writer judges would be most fit and proper for him to speak if present; and in a dialogue the design is similar with respect to the several persons concerned in it. Upon the whole, therefore, a plain, easy, and simple style, suited to the nature of the subject, and the particular characters of the persons concerned, seems to be alike suitable to both.

But as greater skill is required in writing dialogues than letters, we shall give a more particular account of the principal things necessary to be regarded in their composition, and illustrate them chiefly from Cicero's excellent dialogues concerning an orator. A dialogue then consists of two parts; an introduction, and the body of the discourse.

The introduction acquaints us with the place, time, persons, and occasion of the conversation. Thus Cicero places the scene of his dialogues at the country seat of Crassus; a very proper retreat, both for such a debate and the parties engaged in it. And as they were persons of the first rank, employed in the greatest affairs of the state, and as the discourse occupied them for two days, he represents it to have happened at the time of a festival, when no business was done at Rome, and an opportunity was thus afforded them of being absent.

And because the greatest regard should be had in the choice of the persons, who ought to be such as are well acquainted with the subject upon which they discourse, in these dialogues of Cicero the two principal disputants are Crassus and Antony, the greatest orators of that age, and therefore the most proper persons to dispute respecting the qualifications essential for their art. One would think it scarcely necessary to observe that the conference should be held by persons who lived at the time, and thus were capable of conversing together. But yet some good writers have run into the impropriety of feigning dialogues between persons who had lived at distant times. Plato adopted this method, in which he has been followed by Macrobius. But others, who have been willing to bring persons to discourse together who lived in different ages, without such incon- sistency, have written dialogues of the dead. Lucian has made himself most remarkable in this way. As to the number of persons in a dialogue, they may be more or fewer; so many as can conveniently carry on a conversation without disorder or confusion, or they may be only two. Some of Cicero's dialogues have but two, others three or more, and those concerning an orator seven. But it is convenient in some respects that they should all be persons of different characters and abilities; a circumstance which contributes both to the variety and beauty of the discourse, like the different attitudes of figures in a picture. Thus, in Cicero's dialogues last mentioned, Crassus excelled in art, Antony principally by the force of his genius, Catullus by the purity of his style, Scevola by his skill in the law, Caesar by wit and humour; and Sulpitius and Cotta, though young men, were both excellent orators, yet they differed in their manner. But there should be always one principal person, having the main part of the conversation; like the hero in an epic poem or a tragedy, who excels the rest in action, or the principal figure in a picture, which is always made the most conspicuous. In Plato's dialogues this is Socrates, and Crassus in those of Cicero above mentioned.

It is usual likewise, in the introductions, to acquaint us with the occasion of the discourse. Indeed this is not always mentioned; as in Cicero's dialogue concerning the parts of oratory, where the son begins immediately with desiring his father to instruct him in the art. But it is generally taken notice of, and most commonly represented as accidental; the reason of which may be, that such discourses appear most natural, and may likewise afford some kind of apology for the writer in managing his different characters, since the greatest men may be supposed not always to speak with the utmost exactness in an accidental conversation. Thus Cicero, in his dialogues concerning an orator, makes Crassus occasionally fall upon the subject of oratory, in order to divert the company from the melancholy thoughts of what they had been discoursing of before, with relation to the public disorders, and the dangers which threatened their common country. But the introduction ought not to be too long and tedious. Mr Addison complains of this fault in some authors who employ dialogue. "For though," he says, "some of the finest treatises of the most polite Latin and Greek writers are in dialogue, as many very valuable pieces of French, Italian, and English, appear in the same dress; yet in some of them there is so much time taken up in ceremony, that, before they enter on their subject, the dialogue is half over."

We come now to the body of the discourse, in which some things relating to the persons, and others to the subject, are proper to be remarked.

And as to the persons, the principal thing to be attended to is to keep up a justness and consistency of character throughout the whole. And the distinct characters ought to be so perfectly observed, that even from the very words it may be always known who is the speaker. This renders dialogue more difficult than single description, by reason of the number and variety of characters which are to be drawn at the same time, and each of them managed with the greatest propriety. The principal speaker should appear to be a person of great sense and wisdom, and best acquainted with the subject. No question ought to be asked him, nor objection started, but what he should fairly answer; and all that is said by the rest should principally tend to promote his discourse, and carry it through in the most artful and agreeable manner. When the argument is attended with difficulties, one other person or more, of equal reputation, or nearly so, but of different sentiments, should be introduced to oppose him, and maintain the contrary side of the question. This affords an opportunity for a thorough examination of the point on both sides, and for answering all objections. But if the combatants are not pretty equally matched, and masters of the subject, they will treat it but superficially. Through the whole debate, however, there ought not to be the least wrangling, peevishness, or obstinacy; nothing indeed but the appearance of good humour and good breeding, together with a readiness to submit to conviction and the force of truth, according as the evidence shall appear to be on one side or the other. In Cicero, these two characters are Crassus and Antony; and from them Mr Addison seems to have taken his Philander and Cynthia in his Dialogues upon the Usefulness of Ancient Medals, which are formed pretty much upon Cicero's plan. When younger persons are introduced, or such as are not equally acquainted with the subject, they should rather be inquisitive than disputative; and the questions they ask should be neither too long nor too frequent, in order that they may not too much interrupt the debate, nor appear over talkative before wiser and more experienced persons. Sulpitius and Cotta sustain this character in Cicero, and Eugenius in Mr Addison. It is very convenient, however, that there should be one person of a witty and jocose humour, to enliven the discourse at proper seasons, and render it the more entertaining, especially when the dialogue is drawn out to any considerable length. Caesar performs this part in Cicero; and in Mr Addison, Cynthia, a person of a similar turn, opposes Philander in a humorous way. Mr Addison's subject admitted of this; but the seriousness and gravity of Cicero's argument required a different speaker for the jocose part. Many persons ought not to speak immediately after one another; though Scaliger and others think a fourth person may sometimes be permitted to speak in the same scene without confusion. However, if this is not commonly allowed upon the stage, where the actors are present, and may be distinguished by their voice and habit; much less should it be so in a dialogue, where we have only their names to distinguish them.

With regard to the subject, all the arguments should appear probable at least, and nothing should be advanced which may seem weak or trivial. There ought also to be an union in dialogue, in order that the discourse may not ramble, but keep up to the main design. Indeed, short and pleasant digressions are sometimes allowable, for the ease and entertainment of the reader; but every thing should be so managed that he may still be able to carry on the thread of the discourse in his mind, and keep the main argument in view, till the whole be finished. The writers of dialogue have not confined their discourses to any certain space of time, but either concluded them with the day, or broken off when their speakers have been tired, and resumed them again the next day. Thus Cicero allows two days for his three dialogues concerning an orator; but Mr Addison extends his to three days, allowing a day for each. But the same method has not always been observed in composing dialogues; for sometimes the writer, by way of narrative, relates a discourse which passed between other persons. Such are the dialogues of Cicero and Mr Addison last mentioned, and many others both of the ancients and moderns. But at other times the speakers are introduced in person as talking to each other. This, as Cicero observes, prevents the frequent repetition of those words, "he said," and "he replied;" and by placing the hearer, as it were, in the conversation, gives him a more lively representation of the discourse, and thus makes it the more affecting. In this manner, therefore, Cicero wrote his Dialogue of Old Age, in which Cato, who was then advanced in years, recounts the satisfaction of life which may be enjoyed in old age; and, in fact, he tells his friend Diamonds were wholly derived from India, where they were found in detached crystals, accompanied with grains of gold, amongst metallic sand washed down from surrounding mountains. In 1728 a similar territory, loaded with the two most valuable substances in nature, was discovered on the southern continent of the New World. When in pursuit of gold, crystals of diamond were often found; but the labourers being ignorant of their value, laid them aside as curiosities. A miner, who is said to have arrived in Brazil at this time, first directed attention towards them; and, without attempting to appropriate his discovery to his own aggrandisement, he led his comrades to turn their pursuit to the more engaging object. It soon, therefore, attracted the notice of the government, and was shortly afterwards taken possession of in name of the sovereign.

Hitherto the supply of diamonds was entirely confined to Hindustan and the island of Borneo; and, as might reasonably be expected, the opening of a new field, the extent of which was as yet wholly unknown, could not fail to affect the market. The discredit which was at first thrown upon the accounts from Brazil, as also on the purity and perfection of the stones, repressed the fears of the Asiatic dealers, and the increased demand after the purchase of the Pitt diamond, a circumstance which no doubt rendered that gem far more recherché at the gay and luxurious court of France, all tended to increase the demand, and keep it more upon an equilibrium with the increased supply than could possibly have been expected. At a subsequent period, no doubt, the revolution of France interfered with the value of jewels; but the surplus thus produced was soon absorbed by the wealth of Britain, and diamonds of the first water for a long time maintained their ground.

At the present day this perhaps cannot be said to hold good. As a commercial commodity, diamonds must have suffered depression like all others, and may perhaps be valued at from twenty-five to thirty per cent. particularly those beyond the smallest sizes, under the prices which they bore in the times of Tavernier; although Mawe appears to have been anxious to inculcate a different doctrine. After his examination of the Brazilian district, he says there would be no difficulty in calculating the period requisite to work out the whole of the diamond ground in that country; and as many of the mines of Hindustan are considered as exhausted, the period must come sooner or later when diamonds will be no longer to be had.

In both countries the gem is confined within the limits of the tropics. In India, Golconda has always been cited as one of its principal repositories, although none was ever found in the immediate vicinity of that fortress, from the circumstance perhaps of the geological character of the neighbourhood, which is entirely syenitic. It may have arisen, however, from the fact, that the diamond mines of Raolconda and Ganece Purtecal were situated in the territory of the Kootub Shahee kings of Golconda. When that dynasty was overthrown, and their country occupied by the officers of the Mogul emperors, Golconda ceased to be the capital, and Hyderabad, which is only a few miles distant, became the occasional seat of the new government. The territory in which the mines are situated has since been ceded to the East India Company. It lies near Condapilly, on the northern bank of the Kistna, about fifty miles from the sea, and near the Pass of Bezoura, where the river appears at some period to have forced its way through a chain of hills, and to have emptied an extensive lake which had existed to the westward of them. All attempts to work them have been abandoned, as the produce has ceased to refund the expense of labour. The localities of the diamond in Hindustan are so various that it would be almost endless to enumerate them. Those on the Mahanuddy, with those on the Kistna and at Mallavilly, north-west of Ellore, may be mentioned as probably the most productive of this beautiful gem. The island of Diamond. Borneo is the only other eastern locality which can boast of its production. It occurs at Pontiana, in that island, directly under the line, and at Benjarmassin, about three degrees south of the equator. Here it is said to be of a quality superior to that of the gems found in the other Indian localities, and to be distinguished in consequence by the name of Landak, the place they are found in. Here also the diamond occurs in alluvial soil, accompanied with gold. One diamond was found about a century ago, of 367 carats, supposed to be now in the hands of the chief of Pontiana.

From Heyne's account of the working of diamond mines in Hindustan, it seems to afford a very miserable livelihood. He states that the diamond has hitherto been found only in alluvial soil, or in the most recent rocks; and that the stones are not scattered through the whole of these beds, but confined to one rather harder than the rest. The upper stratum, of eighteen inches, consists of sand, gravel, and loam; next there is a deposit of stiff black clay or mud, of about four feet; and next the diamond bed, which is distinguished by a mixture of large rounded stones. It is from two to two and a half feet thick, closely cemented together with clay. Sometimes this stratum is covered with calcareous tuffe. Here shallow pits are excavated, of a few feet in diameter, in such spots as the practice of the workman may induce him to select; he sinks to a depth of a few feet, and searches the bed which he considers most promising for his purposes, and if he meets with little encouragement, he shifts his situation, and proceeds elsewhere. Thus a great deal of the country may be turned to waste and neglected, and, when it comes to be again wrought over more carefully, may give rise to the absurd fancy of regeneration.

The miners, M. Voysey (Asiatic Researches, vol. xv. p. 120) says, are of opinion all over India, that the chips and small rejected pieces of former searchers actually increase in size, and in process of time become large diamonds; and he finishes his paper, by hoping that some future mineralogist would ascertain whether there were any foundation for the vulgar opinion of the continual growth of the diamond; particularly as he hoped at some future period to produce undeniable proof of the re-crystallization of amethyst, zeolite, and felspar, in alluvial soil. This respectable gentleman did not live to bring forward his proofs; but had he been doomed to arrive at the age of the patriarchs of old, we are of opinion he would have been puzzled to produce them.

In Brazil, the diamond is more confined to one spot than in India. The district of Minas Geraes comprehends, as far as we yet know, the whole of the diamond grounds hitherto discovered in the New World. There the workings appear to be carried on more systematically than in India. The operations at the Serra do Frio we have already described in the article BRAZIL (vol. v. p. 199). The Serra do Frio, or cold mountain, is a mountainous platform, having an elevation of from sixteen to eighteen hundred metres. The district over which the diamonds are searched for, extends about sixteen leagues from north to south, by about eight from east to west. It is situated twelve leagues north of Tejuco, on the river Tigitonhonha, which falls into the river San Francisco. By the decomposition of the granite, an conglomerate is formed, composed of rounded white quartz pebbles, and light-coloured sand, to which the natives give the name of cascalho; and it is in this substance that the diamonds are found, along with gold, which is sometimes crystallized. It is exactly similar to some of the samples of the diamond deposits of Hindustan sent to the Royal Society of Edinburgh by Mr Swinton, but differs considerably from others, where a conglomerated sandstone of considerable tenacity has in several instances been sent, as the matrix of the Diamond diamond.

From any thing we are yet able to judge, it does not appear that the diamond has ever yet been seen in a matrix which could be esteemed its original position. Heyne has given two coloured engravings of diamonds in the matrix, and they have the merit of representing very faithfully specimens of this description we have seen at home; but they are in all probability only diamonds accidentally agglutinated in ferruginous matter having no character of a rock. The Musnuddy, which joins the Mahanuddy, is mentioned as affording an indication which might lead to a favourable result in such an investigation. At its confluence with the Maund River, near Chunderpoor, and not farther down than Sonpoor, it is only on the left bank of the river that diamonds are found. Hence the Maund is the point at which the examination should commence; and if the country can be effectually penetrated, it would be well worthy the attention of some enterprising minerologist.

We have no satisfactory geological account of any of the diamond countries; a slight sketch by Voysey, in the article above quoted, is the best that we can refer to. He particularly alludes to a range of hills, called the Nalla Malla, or Blue Mountains, about Cummun, on the Gunlacumnum river, which are composed of schistose rocks, of all varieties, from clay-slate to pure limestone, accompanied with quartz rock, sandstone, sandstone breccia, flinty slate, hornstone slate, and a tufaceous limestone, containing imbedded, rounded, and angular masses of all these rocks. These are bounded on all sides by granite, which appears to pass under and form the base. The only rock of this formation on which the diamond is found is the sandstone breccia. "I have as yet," says he, "only visited the rich mines of Banaganpilly (lying in Heyne's map in 78° 4' by 15° 4'), where the breccia is found under a compact sandstone rock, differing in no respect from that which is found under other parts of the main range. It is composed of a beautiful mixture of red and yellow jasper, quartz, calcedony, and hornstone, cemented together by a quartz paste. It passes into puddingstone, composed of rounded pebbles of quartz, &c. cemented by an argillo-calcareous earth, of a loose friable nature, in which the diamonds are most frequently found."

Heyne states, that in some of the mines in India the diamonds are found entirely broken or crushed, and only of value for pounding; but at the same time thinks it must be owing to carelessness. He mentions also that the diamonds of Cuddapah are carried to Madras to be used for the same purpose, and the price he quotes for a carat of stones fit for brilliants is only seven rupees.

No crystal in nature is more beautiful than that of the diamond. It is sometimes so pure and so pellucid, with its angles and faces so perfectly symmetrical, as to shine like a dew-drop in the rays of the sun. Its primitive form is that of the equilateral octahedron. It passes into the dodecahedron and the cube, presenting modifications in each. The colourless diamond of the first water is the most valuable; but very fine diamonds sometimes present a deep red tinge, also yellow, orange, green, blue, and black. Those which have a slight tint of yellow are often remarkably brilliant, and are said to be of a superior hardness.

The value of diamonds is always calculated in carats, which consists of four grains; but it must be remembered, that the diamond grain differs from the Troy grain, as it takes five of the former to weigh four of the latter, or more exactly one carat = 3·174 gr. Troy.

In valuing diamonds, either rough or cut, the practice is to take the weight in carats, to square that weight, and Diamond—then to multiply the product by such a rate of price as may correspond to the state and quality of the stone; thus, if a natural crystal of diamond be clear, without flaws, and of a favourable shape, the price by which the square of its weight should be multiplied is L2; so that if the stone weigh one carat, its value will be L2, if two carats, $2 \times 2 = 4$, and $4 \times 2 = 8$, or a stone of two carats is worth L8. A stone of ten carats, in the same way, will give $10 \times 10 = 100$, and $100 \times 2 = L200$, the value of a perfect rough diamond of this weight.

If the diamond has been worked into a brilliant of just proportions, the same rule is observed of squaring the weight in carats; but a much higher price is used as the multiplier of the product; as L8 is considered to be the proper multiplier when the stone is perfect in water and shape. Thus a diamond of 5½ carats gives 30½ as its square, and this multiplied by 8 makes L342 as its price. If the stone has been worked into the form which is termed a rose, L6 is used as the multiplier; and if it be of the form termed table-cut, it is still lower.

Considerable modifications, however, must be made in these multipliers, according to the quality of the diamonds and the state of the market. If a brilliant be what is termed "off colour," that is, not absolutely colourless, or if it be in any other way imperfect in shape or purity, a corresponding diminution must be made in the multiplier. Thus a brilliant with a yellow or a milky hue, or with a small speck or flaw, may not be multiplied by more than L4, L5, or L6, according to the nature or extent of the imperfection. The state of the demand in the market must likewise have great influence. At present the demand for good brilliants of one carat and under is greater in proportion to the supply than for heavier stones, and such stones will therefore sometimes cost L10 the carat; whilst there being fewer purchases for the larger sizes, they may often be had in commerce at a lower rate than has been mentioned above.

The finest known diamonds are as follow:

That of the crown of France (Pitt diamond), weighing 136½ carats, the value of which, taken according to the above rule, would be L141,658. The dimensions of this fine stone are stated to be,

Length ........................................... 1-2437 inches. Breadth ........................................... 1-177 Depth .............................................. .859

Weight in Troy grains, 434.

That of the Grand Duke of Tuscany (now Austrian), weighing 139½ carats, valued as above at L153,682.

That of the Emperor of Russia, weighing 193 carats. This diamond is rose cut.

That of the Great Mogul, weighing 279½ carats, also rose cut.

That of the King of Portugal, weighing 1650 carats, being rough, not less than L5,644,800.

It is consequently quite evident that this rule can obtain only among diamonds of moderate size; and if it should establish something by which a price may be named, all else must be left to subsequent arrangement.

Of the remarkable diamonds we have enumerated, the first is that known by the name of the Regent or Pitt diamond. It was found at Pastele, in the Golconda district. It was imported into this country by Mr Pitt, governor of Madras, who purchased it from a native for 48,000 pagodas, about L20,400 at the exchange of the day, and after being offered to different crowned heads in Europe, was purchased by the regent of France in 1717 as a jewel for the crown. It was placed by Napoleon in the hilt of the sword of state, and, according to Brard, the price paid for it was 2,250,000 francs; Jeffreys calls it L125,000, and other authors say L130,000. Any of these, however, although by much the largest price ever paid for any jewel, is not Diamond equal to the rule of value. This is esteemed the finest and most perfect diamond known.

The second was purchased for a hit of rock-crystal, on a stall in the market-place of Florence, at the cost of a few pence; it is of a beautiful lemon-yellow colour, and is now in the possession of the house of Austria. The diamond mentioned as the property of the Emperor of Russia ornaments the top of his sceptre. It is of the size of a pigeon's egg, and is said to have been the eye of an Indian idol pilaged by a deserter from the French service, who had the address to get himself installed as a priest in the service of the Malabar deity at Seringham, as narrated by Dutens. The Empress Catherine purchased it for L90,000, together with an annuity of L4000.

The Great Mogul is described by Tavernier as an irregularly-shaped diamond, but cut and polished. It was found at Colore, in the district of Golconda, in the year 1550; and is said to have weighed 900 carats before cutting, but this appears a most enormous sacrifice. Of the Brazilian diamond some suspicions have been entertained. It has been insinuated that it is only a mass of very fine white coloured topaz, and it is not likely that the king of Portugal will run the hazard of ascertaining the fact.

The supply of diamonds from Brazil, according to Baron d'Eschwege, during the eighty-four years from 1730 to 1814, was at the rate of 36,000 carats per annum; but the return from the registers of the administration of the diamond mines from 1800 to 1806 was only 19,000 carats. It is also added, that the revenue derived by government during the first period was only eighteen or nineteen francs the carat, whilst from forty to fifty were obtained during the last; a certain indication of a diminished supply. A singular circumstance is noticed with respect to the uniformity of the diamond ground of Do Frio. The same cubic mass of cascalho will yield, on washing, pretty nearly the same number of carats, in large or small diamonds, so that the superintendent can calculate on the probable produce of the washing.

Large stones do not abound in Brazil, but there are some of considerable dimensions. Mawe mentions one from the little rivulet D'Albaite of 120 carats, but they do not often exceed from eighteen to twenty.

The prices of diamonds quoted by Heyne, who visited with a scrutinizing eye the principal mines of Hindustan, differ from those laid down by the rule of Tavernier and Jeffreys. Without attempting to reconcile them, we shall quote the value which the Hindus put upon what they consider as the best, and denominate the Brahma diamond; it is sold by the manjalin, which is equal to two carats, and each carat at the price of ten pagodas.

| One manjalin | 10 Madras pagodas | |--------------|------------------| | Two | 24 | | Three | 40 | | Four | 80 | | Five | 100 | | Six | 150 | | Seven | 250 | | Eight | 400 |

He adds that these are the prices of stones free from speck, flaw, or crack. Cut stones are valued in a different way.

The most remarkable circumstance in the history of the diamond is to be found in the nature of its composition. This proud, this imperial ornament, which has ever occupied the summit of the diadem, this most brilliant of gems, and hardest of all known bodies, is, after all, but a morsel of charcoal, which has been made to yield to the rays of the sun, and dissolve into a noxious vapour. As early as 1607, Bastius de Boodt threw out the hint that Diamond was inflammable. In 1673 Boyle discovered that when it was exposed to a great heat it was dissipated into acid vapour. In 1694, the experiments of Boyle were confirmed by those of Cosmo III. Grand Duke of Tuscany, with his celebrated burning glass. About the same time, but whether before or not is uncertain, Sir Isaac Newton was led, from the great refractive power of the diamond, to pronounce it "an unctuous substance coagulated." Lavoisier proved it to be composed of carbon, by throwing the sun's rays concentrated by a powerful lens upon a diamond inclosed in a vessel with oxygen gas; when the diamond and the oxygen disappeared, and carbonic acid was generated. Sir George Mackenzie repeated the experiments of Boyle in 1800; and, finally, when Sir Humphry Davy visited Florence in 1814, the experiment of the grand duke was performed again with the same lens; and mineralogists no longer hesitated to place the gem amongst inflammable bodies.

According to Ellicot, the specific gravity of Brazil diamonds is 3·513, and of India diamonds 3·519. The former is the mean of four, the latter of ten experiments.

Diamond cutting was little understood till 1476, when an artist of the name of Berghen, residing at Bruges, introduced the practice of using diamond powder for forming and polishing the facets. Holland, in consequence, long maintained a monopoly of this trade; and to this day the smaller diamonds are almost entirely manufactured for the European market, at Amsterdam. The Pitt diamond was, however, cut and polished in London, as most of the larger sized stones continue to be. It is a very laborious and tedious operation. The grinding into the required form is entirely done by the hand. Two stones are cemented to the ends of tool handles, and rubbed with a powerful pressure against each other, a leaden model being first taken of the rough stone intended to be cut. The faces are thus determined. The two stones are then rubbed together over a little metal box having a double bottom, the upper one being loose and perforated with small holes, through which the diamond dust passes, and is carefully preserved. The desired form being thus obtained, the dust is afterwards used in polishing the faces of the diamond, mixed up with sweet oil, on a common lapidary's wheel, and the brilliancy of the gem brought out. The period of constant work required to reduce a stone of between twenty-four and thirty carats to a regular form will extend to at least seven or eight months constant work. The Pitt diamond was said to occupy two years. From the outline in Plate CCII. fig. 1, there was a great deal of extraneous matter to reduce, and that space of time may very likely have been required. When the mass to be removed is of such a size as to render it of importance to keep it entire, the piece is cut off by means of a steel wire, extended on a bow of cane or whalebone, anointed with diamond powder. This process is very commonly adopted in India. The diamond is sometimes also split by means of a chisel under a sharp stroke of a hammer; but this means requires great firmness of mind and dexterity of hand, for a valuable stone is sometimes destroyed by an unlucky blow.

The forms into which the diamond is cut are the brilliant, the rose, and the table. The first is composed of a principal face, which is called the table, surrounded by a fringe composed of a number of facets, which is all that is visible above the bezel when set. The proportion for the depth should be half the breadth of the stone, terminated with a small face, parallel to the table, and connected with the surface by elongated facets. As the octahedron is the most common natural form of the stone, and the brilliant cut being by far the most advantageous in point of effect, and the most economical form that can be adopted, it is hence preferred. The others are suggested by the shape of the mass.

The rose is entirely covered with facets on the surface, and is flat below. The table form is adopted in consequence of the shape of the mass, whether crystal or fragment, and produces the least effect. It is principally used in India, where the native jewellers cleave stones into plates, having often a large surface with little proportioned weight or brilliancy, except at the edges, which are ornamented by being cut into facets. The great diamond of the Mogul emperor, called Derriah Noor, is of this description; that called Koh-e-noor is rose-cut.

Much of the value of diamonds depends on the cutting of the stone. A late celebrated philosopher, who required a piece of diamond for philosophical purposes, found a large mass in the hands of a jeweller. It was of an awkward form, and presented a flaw which very greatly deteriorated its value, as, in consequence of the refraction and reflection which took place within the mass, the flaw seemed to occupy nearly the whole of the interior. The gentleman, however, was not afraid. He paid a large sum for the stone, directed the workman in cutting it, amputated the piece he wanted, separating the flaw, and sold the remainder back to the jeweller, after being properly cut and polished, for double the price he paid for it.

Hopes were recently excited, that a new diamond district had been discovered in Siberia, by the celebrated traveller Humboldt. He thought he had met with appearances in a territory belonging to Count Demidoff, analogous to that of Minas Geraes, and recommended a search for the gem. But as two years have since elapsed without any confirmation of this suggestion, the old localities of Asia and Brazil are likely to remain without competition.

Explanation of the Plate, No. CCII.—The three figures at the top, No. 1, 2, 3, are representations of the Regent or Pitt diamond, the Great Mogul, and the Grand Duke, of the full size and form. No. 4 presents the brilliant cut, looked at perpendicularly. No. 5, the same sidewise. No. 6 and 7 also represent the brilliant before it undergoes the process of re-cutting. No. 8 and 9 are the vertical and lateral appearances of the rose-cut diamond; and No. 10 and 11, that of the table-cut. The scale No. 12 exhibits the sizes of the set diamond within the bezel, together with the depth of the stone, and the number of carats a diamond of that size is likely to weigh. This estimate can only be an approximation to the exact weight; but the weight of a set stone may thus be very nearly ascertained. No. 13 is the figure of the octahedral diamond seen perpendicularly, with the table traced where the stone should be cut; and No. 14 is the same crystal seen laterally, with the table and the opposite face also traced. By these figures it will be seen how much more advantageous it is to adopt the brilliant form than any other.

Diamonds have been imitated with great success by the French artists. To this composition, to which they give the name of strass, they not only communicate the adamantine lustre of the zircon, but succeed in giving it such a similitude to the real stone in all respects, hardness excepted, that it is nearly impossible for unpractised eyes to detect the difference. Recently quartz has been used with great effect to form the faces of fictitious stones.

Diamond used by Glaziers, is an instrument made of steel or iron, into the point of which a diamond is introduced and fixed by solder. Care must be taken to place the gem so that, by applying the instrument in a particular position, the angle of the crystal will come in contact with the glass.