STEAMNAVIGATION

THE application of steam-power to navigation is one of the most wonderful triumphs of human ingenuity. By this power vessels of gigantic size are impelled across the trackless ocean; and, in spite of its storms and resisting tides, establish a chain of communication between the shores of the remotest regions, as safe and as certain as if connecting the cities of a continent. Thirty years have scarcely yet elapsed since the first steam-ship of traffic was launched on the Hudson, and now there is hardly a navigable river or an inland lake whose waters are not agitated by the steam-boat paddle, and its atmosphere darkened by her smoke; while even the ocean itself is crossed in almost every direction by lines of steam-ships of immense size, and of beautiful construction. Many individuals have claimed the merit of inventing an art so pregnant with interest to mankind; and almost every civilized country contends for the honour of its birthplace. If the mere suggestion of the application of steam-power to the purposes of navigation entitle an individual to the credit of having invented the art, there are, doubtless, many who may be regarded as its inventors; for this suggestion was repeatedly made almost as early as the invention of the steam-pump, although from the nature of steam machinery, then and for long after, no advantage could be derived from it. To show how the ingenious of that time were led to propose steam as a motive power in navigation, we shall give a brief account of the contrivances which had been devised for the propulsion of vessels.

The substitution of other apparatus than oars, and of other power than human labour, to impel vessels in a calm or against the wind, is of unknown antiquity. The Egyptians are said to have used, in their boats, wheels like the paddle-wheels of the present day, but moved by oxen working in a gin on the deck of the vessel. Valerius, in his treatise De Re Militari, gives an account of paddle-wheel boats used by the Romans as transports, the paddle-wheels being driven by men or by horses; and we have, from many sources, abundant evidence of the existence of similar boats elsewhere. In a book published in London in 1578, called Inventions and Devices, by William Bourne, we find the following passage: "And farther more, you may make a boat to go without oars or sail, by the placing of certain

wheels on the outside of the boat, and so turning the wheels by some provision, and so the wheels shall make the boat goe." Thus we see that the means of making the boat go by paddle-wheels was already discovered, and the "some provision," by which these paddle-wheels were to be moved, was the desideratum. Horses, oxen, and human power had already been used for this purpose; and the first indication of some different power occurs in the Marquis of Worcester's Century of Inventions, published in 1663. The marquis, describing his quintessence of motion, says, "By this I can make a vessel of as great burthen as the river can bear to go against the stream, which, the more rapid it is the faster it shall advance, and the moveable part that works it may be, by one man, still guided to take the best advantage of the stream, and yet to steer the boat to any point. And this engine is applicable to any vessel or boat whatsoever, without being therefore made on purpose, and worketh these effects—it roweth, it draweth, it driveth, (if need be,) to pass London Bridge against the stream at low water; and, a boat laying at anchor, the engine may be used for loading or unloading." What the marquis's quintessence of motion was, or how applied to the moving of the vessel, we have not now the means of discovering; but, in his proposed applications of it, he has more than anticipated all that has yet been done; for we do not yet employ our steam-engines for loading or unloading. Savary, the inventor of the next steam-engine, proposed to apply his engine to impel boats. The only way, however, in which a rotatory motion could be derived from his engine was, by it to raise water into an elevated cistern, whence it could fall upon the floats of a water-wheel. This clumsy machine was not well adapted for a boat; and we hear nothing of its application. About the year 1688, the ingenious Dr Papin, who had been engaged with the project of an atmospheric vacuum-engine for moving machinery, proposed to form a vacuum in his cylinder with gunpowder, as had been proposed by Hautefeuille ten years before, and by Huyghens in 1680; but this scheme being found impracticable, he proposed, about two years afterwards, "to turn a small surface of water into vapour, by fire applied to the bottom of the cylinder which contains it, which vapour forces up the plug or piston in the cylinder to a considerable height, and which, as the vapour condenses, descends again by air pressure, and is applied to raise water out of the mine." Besides raising water from mines, he proposed also

For these historical notices, ending in p. 693, we are not indebted to the same contributor who wrote the rest of the article.

Na-by a motion derived from the piston-rod of his engine, to impel the paddles of a boat. Here, with the discovery of the high-pressure engine within his reach, Papin relinquished his experiments; and Newcomen, adopting his cylinder and piston, and Savary's mode of condensation, a few years afterwards completed the atmospheric engine. The difficulty of converting the reciprocating motion of the atmospheric engine into a rotatory motion was the great bar to the use of it in any other way than for pumping water. Yet not a few speculators are to be found at this time inventing other means of propelling vessels than by paddle-wheels, so as to take advantage of the single reciprocating action of the engine. In 1730, Dr John Allen proposed to give motion to vessels by forcibly ejecting a stream of water or current of air from their stern; a scheme which, since his time, has been again and again invented, patented, and abandoned. Seven years after his proposal, Jonathan Hulls published an account of a steam-boat invented by him. In this boat, he had two paddle-wheels suspended in a frame projecting from its stern. In the body of the boat were two atmospheric engine cylinders with their pistons: to each piston one end of a rope was fastened; the rope was then carried round a pulley on the corresponding paddle-wheel, and one end was allowed to hang free, with a weight attached to it. When one of the pistons was pressed down in its cylinder by the weight of the atmosphere it pulled its rope, and, consequently, moved round the paddle-wheel in a degree due to the length of the stroke and the diameter of the pulley. While the piston was ascending in the cylinder, on the admission of the steam, the counterbalance weight, at the outer end of the rope, dragged round the pulley in the contrary direction; but the pulley being attached to the paddle-wheel by a ratchet-wheel, the latter remained stationary during the retrograde motion of the former. There being two cylinders and two paddle-wheels in the boat, it was so ordered that one should be in motion while the other remained stationary, and that thus the boat's motion should be continuous. However ingenious this plan of a steam-boat may be, we find no evidence that it was ever reduced to practice; but in a tract which Hulls published in 1737, he meets, and combats in a most masterly manner, every objection which he conceives might be urged against his project.*

In 1757, the celebrated Daniel Bernoulli, in an essay which obtained a prize from the Academy of Sciences, after demonstrating the effect of many mechanical contrivances which might be substituted for oars in moving vessels, suggests paddle-wheels moved by steam-power or the force of gunpowder. Another of the essayists, Gautier, a canon of Nancy, in suggesting the same mechanism and the same power, shows very great fertility of invention, and skilful application of mechanical resources in the adaptation of the different parts of the machinery.

In 1759, Mr J. A. Genevois, a minister of Berne, invented a species of propellers, which, like a duck foot, would expand, and present a large surface to the water when moved against it, but would fold up into small compass when moved in an opposite direction. It is scarcely necessary to say, that these duck feet oars failed; but it is a melancholy fact, that similar apparatus has been frequently re-invented since the days of the

pastor of Berne, and with the same degree of practical Steam-Navigation.

The Comte d'Auxiron, in 1774, under the auspices of a company formed for the purpose, made some experiments with steam-boats on the Seine. These unfortunately failed; but M. J. C. Perier, who had been present, repeated them with improved machinery, a year or two later. His success was so indifferent as to offer no inducement to him to continue his experiments. It is unnecessary to swell the present work with examples such as these; and we shall therefore at once proceed to the time of Watt, whose labours gave to the steam-engine its power of almost universal applicability, and eminently fitted it for the moving of paddle-wheels.

Leaving undescribed the experiments of the Marquis de Jouffroy on the Seine in 1782, and the attempts of Rumsey, of Fitch, and of Evans in America, between the years 1775 and 1787, which were attended with no beneficial effect, we proceed to notice the first attempts which were perfectly successful, and to which we more immediately owe the benefits of steam navigation. These were made in 1787, by a Scottish gentleman, Patrick Miller, Esq. of Dalswinton in Dumfries-shire, who, in that year, published an account of some experiments which he had made on the best mode of impelling single, double, and triple vessels, by the power of men and of horses applied to paddle-wheels. In this publication, Mr Miller states, "I have reason to believe that the power of the steam-engine may be applied to work the wheels, so as to give them quicker motion, and consequently to increase that of the ship. In the course of this summer I intend to make the experiment." He owed the suggestion of the steam-engine to a young man, Mr James Taylor, who resided in his family as tutor, and who had assisted him in his experiments; but neither Mr Miller nor Mr Taylor could devise a way of applying the engine to the boat. In this dilemma, Taylor suggested that they should have recourse to the aid of an old school-fellow of his, Mr William Symington, an engineer, at that time assiduously employed in endeavouring to adapt the steam-engine to wheel carriages. Mr Taylor seems to have sent an account of their project to Mr Symington, as we find the latter thus writing to the former, on the 20th August 1787: "I must make some remarks on your summer's inventions, which, if once made to perform what their author gives them out for, will undoubtedly be one of the greatest wonders hitherto presented to the world, besides its being of considerable emolument to the projector. Great success to you, although overturning my schemes." In the winter of the same year, Mr Miller was introduced to Mr Symington in Edinburgh, and saw the model of his locomotive carriage. Convinced of the perfect applicability of a similar engine to drive the paddle-wheels of a boat, Mr Miller gave orders for the construction of an engine on the same plan, under the direction of Symington and Taylor. The engine was accordingly made in Edinburgh, and sent to Dalswinton, and by them put together in October 1788. The engine, in a strong oak frame, was placed on one side of a twin or double pleasure boat on Dalswinton lake. The boiler was placed on the opposite side, and the paddle-wheels in the middle. In the middle of October, the machine was first put in motion; and the ingenious inventors had the gratification of witnessing the perfect success of the first steam-boat. Although the cylinders of the engine were but four inches in diameter, yet the boat attained a speed of five miles an hour. Mr Miller, anxious to try the experiment on a larger scale, commissioned Mr Symington to purchase a gabert, or large boat at the Forth and Clyde Canal, and to get suitable engines

* A Description and Draught of a new invented Machine for Carrying Vessels or Ships out of, or into, any Harbour, Port, or River against Wind and Tide, or in a Calm: for which his Majesty has granted Letters Patent, for the sole benefit of the author, for the space of fourteen years. By Jonathan Hulls. London, 1737, 12mo.

Steam-Na-vigation. constructed at Carron. Every thing being completed, a trial took place on a level reach of the Canal, of about four miles in length, at Lock Sixteen. The trial was made in presence of many spectators, who were however disappointed in their expectations, owing to the breaking of the paddle-wheels. Stronger wheels were obtained, and another trial took place on the 26th December 1789, and the vessel moved at the rate of about seven miles an hour. Next day and afterwards the experiment was repeated with equal success; and the following account of it was transmitted by Lord Cullen to several of the Edinburgh newspapers:—"It is with great pleasure I inform you that the experiment which some time ago was made upon the great canal here by Mr Miller of Dalswinton, for ascertaining the powers of the steam-engine when applied to sailing, has lately been repeated with great success. Although these experiments have been conducted under a variety of disadvantages, and with a vessel built formerly for a different purpose, yet the velocity acquired was no less than from six and a half to seven miles an hour. This sufficiently shows that, with vessels properly constructed, a velocity of eight, nine, or even ten miles an hour may be easily accomplished, and the advantages of so great a velocity in rivers, straits, &c., and in cases of emergency, will be sufficiently evident, as there can be few winds, tides, or currents which can easily impede or resist it; and it must be evident that, even with slower motion, the utmost advantage must result to inland navigation." It is much to be regretted that Mr Miller, having made so successful an experiment, carried his attempts no further. The boat was dismantled and laid up at Carron; and this ingenious and public-spirited gentleman directed his attention to other objects. His pursuits had a greater tendency to improve the condition of his country, than to enrich his own family.

In 1793, Rumsey, who, as we have already stated, had been unsuccessful in his experiments in America, got some American residents in London to defray the expenses of another experiment there. He, however, died before his boat was finished; and when it was got afloat by those engaged with him, it attained a speed of four miles an hour against wind and tide. The propulsion of this boat was effected, on the principle of Dr John Allen's, by ejecting a stream of water at the stern.

In 1795, Earl Stanhope revived the pastor of Berne's duck feet oars; but he could not cause his vessel to move at a higher rate than three miles an hour.

In the year 1801, Thomas Lord Dundas employed Mr Symington to make a tug-boat for dragging vessels on the canal. With this view, a series of experiments were made between 1801 and 1802, at a cost of £3000. In March 1802, Lord Dundas, Mr Speirs of Elderslie, and several other gentlemen, being on board of the newly-constructed tug-boat, which was named the Charlotte Dundas, it "took in drag," says Mr Symington, "two loaded vessels, each upwards of 70 tons burden, and with great ease carried them through the long reach of the Forth and Clyde Canal to Port Dundas, a distance of 19½ miles in six hours, although the whole time it blew a very strong breeze right ahead."

In consequence of an impression in the minds of some of the canal proprietors, that the paddle-wheels of the boat injured the banks of the canal, the project of the steam-tug was with great reluctance abandoned, and the boat was laid up in a creek of the canal, where it remained for many years exposed to public view. A year after this most successful experiment, Mr Fulton, an American, made a similar experiment on the Seine at Paris, under the auspices of the American chancellor, Mr Livingstone. Owing to a miscalculation of the strength of the boat, it had no sooner received the weight

of the engine than it broke through the middle, and went to the bottom. Not disheartened, Fulton set about building a new vessel; and in August 1803 he launched it with its machinery. This vessel was 66 feet long and 8 feet wide; but moved so slowly, that we may describe the experiment as a failure. He afterwards came to Scotland, and saw Mr Symington's vessel. Of this visit, a memorial of Mr Symington's, which we have before quoted, gives the following account:—"When engaged in these last experiments, I was called upon by Mr Fulton, who very politely made himself known, and candidly told me that he was lately from North America, and intended to return thither in a few months, but having heard of our steam-boat operations, could not think of leaving this country without first waiting upon me, in expectation of seeing the boat, and procuring such information regarding it as I might be pleased to communicate; he at the same time mentioned, however advantageous such invention might be to Great Britain, it would certainly become more so in North America, on account of the many extensive navigable rivers in that country; and as timber of the first quality, both for building the vessels, and also for fuel for the engine, could be purchased there at a small expense, he was decidedly of opinion it could hardly fail, in a few years, to become very beneficial to trade in that part of the world; and that his carrying the plan to North America could not turn out otherwise than to my advantage; as, if I inclined it, both the making and superintendence of such vessels would naturally fall upon me, provided my engagements with steam-boats at home did not occupy so much of my time as to prevent me from paying any attention to those which might afterwards be constructed abroad. Mr Fulton having thus spoken, in compliance with his most earnest request I caused the engine-fire to be lighted up, and in a short time thereafter put the steam-boat in motion, and carried him from Lock No. 16, where the boat then lay, four miles west the canal, and returned to the place of starting, in one hour and twenty minutes, to the great astonishment of Mr Fulton, and several gentlemen who at our outset chanced to come on board. During the above trip, Mr Fulton asked if I had any objections to his taking notes regarding the steam-boat; to which question I said, none, as I considered the more publicity that was given to any discovery intended for general good, so much the better; and having the privilege secured by letters patent, I was not afraid of his making any encroachment upon my right in the British dominions, though in the United States I was well aware I had no power of control. In consequence, he pulled out a memorandum-book, and, after putting several pointed questions respecting the general construction and effect of the machine, which I answered in a most explicit manner, he jotted down particularly every thing then described, with his own remarks upon the boat, while moving with him on board along the canal; but he seems to have been altogether forgetful of this, as, notwithstanding his fair promises, I never heard any thing more of him, till reading in a newspaper an account of his death.

"From the above incontrovertible facts, which can be corroborated by a number of persons of respectability living at this day, it is very evident that commerce is not indebted to North America for the invention of steam-packets, it being hereby established beyond the possibility of doubt, to be truly British, both in the idea and practice; and that Mr Fulton's steam-vessel did not make its first appearance in the Hudson river earlier than 1806 or 1807, four years at least posterior to his having been on board the Charlotte Dundas steam-boat, and minutely examined it, when at work on the Forth and Clyde Canal,

Na- and eighteen years later than the date of the first experi-
ments made by me upon steam-boats, on the lake at
Dalswinton, Dumfries-shire, in Great Britain."

Fulton, having obtained what information he could, or-
dered, under an assumed name, it is said, a steam-engine
from Bolton and Watt. He shortly afterwards returned
to America, and in conjunction with Mr Livingstone ob-
tained a patent, securing to them the prospective advan-
tages of steam navigation in America, by what they
rather insincerely termed their invention of steam-boats.
In 1806 Bolton and Watt's engine arrived, and in 1807
the first steam-vessel in America was launched on the
Hudson river. It was called the Clermont, which was the
name of Livingstone's residence. In spite of the advan-
tages which it possessed over the Scottish vessels, in hav-
ing better engines, and in its projectors having the benefit
of Symington's experiments, it was a comparative failure,
attaining at the utmost a speed of only five miles an hour.
The boat had not been long under weigh, on its first trip,
when Fulton ordered the engine to be stopped. Having
observed that the paddle-wheel floats were too deeply
immersed in the water, he shifted them nearer to the
centre of the paddle, so that they did not enter so deeply
into the water; and this alteration had the effect of in-
creasing the speed of the vessel.

Shortly after this first experiment, it was announced
that the Clermont would sail from New York to Albany;
and of this first voyage the following account was sent
to the Editor of the American Citizen newspaper, by
Fulton himself:—

"Sir,—I arrived this afternoon, at four o'clock, in the
steam-boat from Albany. As the success of my experi-
ment gives me great hopes that such boats may be ren-
dered of great importance to my country—to prevent
erroneous opinions, and to give some satisfaction to the
friends of useful improvements, you will have the good-
ness to publish the following statement of facts. I left
New York on Monday at one o'clock, and arrived at
Clermont, the seat of Chancellor Livingstone, at one
o'clock: time, 24 hours; distance, 110 miles. On Wed-
nesday I left the chancellor's at nine in the morning, and
arrived at Albany at five in the afternoon: distance,
40 miles; time, 8 hours. The sum is 150 miles in 32 hours,
equal to nearly 5 miles an hour, &c.—ROBERT FULTON."

During the same season, the boat made many voyages
between New York and Albany, and in these she met with
not a few accidents, arising chiefly from the defective con-
struction of her paddle-wheels, which were of cast-iron,
and had no support beyond the vessel. She was likewise
injured by the sailing vessels, whose owners, dreading the
intruder, ran them against her. The Clermont was at
length laid up during the winter; and being enlarged and
strengthened, she was again, in the spring of 1808, em-
ployed as a passage-boat between the same stations, and
continued during the summer crowded with passengers.
The success of their first vessel induced Messrs Living-
stone and Fulton to build other two vessels, the Car of
Neptune, of 300 tons, and the Paragon, of 350 tons.

Thus it was that steam navigation in America origi-
nated; and the enthusiastic and speculative Fulton en-
joys the honour of having first shown to the world its
commercial value. It is now proper time to mention
that Fulton had been aided in his experiments on steam
navigation by Mr Henry Bell, by whom the first steam
passage vessel in Britain was constructed. The nature
of this connexion will be better seen from Mr Bell's own
account of it, which was addressed to the Editor of the
Caledonian Mercury in 1816.

"Sir,—I observed in your paper lately a paragraph
respecting steam-boats, in which the Americans claim
the right to the discovery which is become of so much
VOL. XX.

utility to the public. On this account I propose to give Steam Na-
vigation. you a full statement of what I conceive to be the truth. Mr Miller of Dalswinton first wrote upon the method of
moving or impelling vessels or rafts through water by
paddles, wrought by a capstan, or by the wind, in the
manner of a wind-mill, which idea he afterwards gave to
all the different courts in Europe. It will be recollected
by most people in this country, that the French proposed
to erect rafts for conveying troops to invade this country,
by means of Mr Miller's wind-mill or capstan plan; for,
it may be stated that this gentleman built two vessels at
Leith, and put them in motion upon his new improvement,
and even sent one of them to the King of Sweden as a
present. After this, he thought that an engine could be
so constructed as to be applied to work his machinery
for the moving of his paddles; and accordingly he em-
ployed an engineer to put his plans in execution; but
they failed for want of being properly executed. But to
give you a more correct account of the manner Mr Ful-
ton, the American engineer, came to the knowledge of
steam-boats, that gentleman had occasion to write me
about the plans of some machinery in this country, and
beg the favour of me to call on Mr Miller of Dalswinton,
and see how he had succeeded in his steam-boat plan;
and if it answered the end, I was to send him a full
drawing and description of it, along with my machinery.
This led me to have a conversation with the late Mr
Miller, and he gave me every information I could wish
for at the time. I told him where, in my opinion, he had
erred, and was misled by his engineer; and at the same
time I told him, that I intended to give Mr Fulton my
opinion on steam-boats. The friends of Mr Miller must
have amongst their papers Mr Fulton's letter to me; for
I left it with Mr Miller. Two years thereafter I had a
letter from Mr Fulton, letting me know that he had con-
structed a steam-boat from the different drawings of the
machinery I had sent him out, which was likely to an-
swer the end, but required some improvement on it.
This letter I sent to Mr Miller for his information, which
must also be amongst his papers. This letter led me to
think of the absurdity of writing my opinion to other
countries, and not putting it in practice myself in my
own country; and from these considerations I was
roused to set on foot a steam-boat, for which I made a
number of different models before I was satisfied. When
I was convinced that they would answer the end, I con-
tracted with Messrs John Wood and Company, ship-
builders in Port-Glasgow, to build me a steam-vessel
according to my plan, 40 feet keel, and 10 feet 6 inches
beam, which I fitted up with an engine and paddles, and
called her the Comet; because she was built and finished
the year that a comet appeared in the north-west part of
Scotland. This vessel is the first steam-boat built in
Europe that answered the end, and is at this present
time upon the best and simplest method of any of them;
for a person sitting in the cabin will hardly hear the
engine at work. She plies on the Frith of Forth betwixt
the east end of the great canal and Newhaven, near
Leith. The distance by water is 27 miles, which she
performs, in ordinary weather, in 3½ hours up, and the
same down. There were many attempts to make steam-
boats in this country before this one, but none of them
ever answered the end; and even three years after the
Comet was set a-sailing, there was a number of our first-
rate engineers joined together, and obtained a patent for
what they conceived a new discovery on the paddles for
impelling the vessel forward. They were disappointed
in their plan, and had to return to the model of the
Comet.

The Comet was a vessel of about 25 tons, and her
engine, which was a vertical one, exerted about three

Steam Na-horses power. Bell's success immediately excited competition; and a vessel called the Elizabeth, 58 feet in deck, and with an engine of 8 horse power, was started by Mr John Thomson on the 9th of March 1815. The spirit of enterprise was now roused, and steam-boats rapidly succeeded each other, every succeeding one exceeding its predecessor in power and beauty. No longer timidly confining themselves to the navigation of rivers, the projectors of those steam-ships boldly steered into the deep waters, crossing the channel between Great Britain and Ireland, and performing the dangerous coasting voyages between Glasgow and Liverpool, Leith and Aberdeen, and Leith and London.

The first person who ventured beyond the precincts of a river was in all probability R. L. Stevens of Hoboken. This gentleman had been associated with Chancellor Livingston, previously to the connexion of the latter with Fulton, and had brought his experiments to a successful issue nearly as soon as Fulton and Livingston. Fulton having, however, secured to himself the exclusive privilege of navigating by steam in the state of New York, Stevens at once conceived the bold idea of taking his vessel by sea from the Hudson to the Delaware. To Mr Stevens many of the improvements of steam navigation are to be ascribed. He introduced the modifications of Watt's engine, which we have represented in Fig. 2, p. 693, still in use in American vessels. He introduced engines of long stroke; and, as a necessary consequence, a long crank, and the further peculiarity of upright guides for the piston-rod, instead of the old parallel motion. To him we likewise owe the paddle-wheel with divided boards, by which the resistance of the water was rendered more uniform, and the concussions of the common paddle-wheels avoided. He improved the shape of the American steam-vessels, by substituting for the full round bows and sterns a fine entrance and a fine run. By this, and by making the length of his vessels eight or ten times their beam, he succeeded in raising their rate of sailing from nine to thirteen miles an hour.

Reverting to Britain, we find from the first introduction of Bell's Comet in 1813, steam navigation gradually improving as an art. The vessels were, however, of small dimensions, of low proportion of power, and of little speed, until the year 1818, when Mr David Napier directed his attention to the improvement of steam navigation. It is to this gentleman that Great Britain owes the introduction of deep sea communication by steam vessels, and the establishment of post-office steam-packets. In 1818, Mr Napier established between Greenock and Belfast a regular steam communication, by means of the Rob Roy, a vessel built by Mr William Denny of Dunbarton, of about 90 tons burden, and 30 horse power. For two winters she plied with perfect regularity and success between these ports, and was afterwards transferred to the English Channel, to serve as a packet-boat between Dover and Calais. Having thus ventured into the open sea, Mr Napier was not slow in extending his range. Soon after, Messrs Wood built for him the Talbot, of 120 tons. With two of Mr Napier's engines, each of thirty horse power, this vessel was in all respects the most perfect of her day, and was formed on a model which was long in being surpassed. She was the first vessel that plied between Holyhead and Dublin. About the same time he established the line of steam ships between the stations of Liverpool, Greenock, and Glasgow. For the traffic of these stations he built the Robert Bruce, of 150 tons, with two engines of 30 horse power each; the Superb, of 240 tons, with engines of 35 horse power each; the Eclipse, of 240 tons, with two engines of 30 horse power each. All these were established as regular deep sea traders before

the year 1822, on a station which has not since been surpassed for the power, beauty, and speed of its steam vessels.

In 1822 was built by Messrs Wood on the Clyde, the James Watt steam-vessel, to ply between Leith and London. This vessel was of 448 tons measurement, and she carried two engines of fifty horse power each, made by Messrs Watt and Bolton, and completed entirely under the superintendence of Mr Brown of that firm. The James Watt was remarkable for having its paddles moved, not directly by the engine, but through the interposition of toothed wheels, so that the number of revolutions of the axis of the engine was greater than that of the paddles. With the exception of the low proportion of its power to its tonnage, the James Watt possesses almost all the qualities of the most improved vessels of the present day.

The next great advance in the art was made in 1826, when the first of the leviathan class of steamers, the United Kingdom, was constructed. This steam-ship was 160 feet long, 26½ feet beam, and 200 horse power. She was built by Mr Steele of Greenock, and the engines were constructed by Mr Napier. Mr David Napier was also one of the first persons to introduce surface condensation in marine engines. He used it successfully in the Post-Boy, a steam-vessel built by him. The condenser was composed of a series of small copper tubes, through which the steam passed towards the air-pump; and, a constant current of cold water encircling the pipes, the steam was cooled and returned into water, which was again sent into the boiler for conversion into steam, without being mixed with the cold salt-water, which, in the usual plan, is injected into the condenser. But, like Watt, Cartwright, and others, who have tried this system both here and in America, he did not find the rapidity of condensation sufficiently great, and he returned to the old system of condensation by jet. Some years afterwards, however, he reverted to this system in peculiar circumstances which rendered it desirable; and, using flat plates instead of tubes, was again perfectly successful, and plied for years with no other condenser. But, like all the other cases where it has been introduced, the advantages of the system were not reckoned equivalent compensation for its disadvantages. The plan of condensation by tubes, again introduced at a recent date by Mr Hall, has been tried in numerous vessels, in some of which it has been abandoned, and in others it still continues to be employed.

The next change introduced very extensively into steam-vessels by Mr Napier, was the use of an upright or vertical steam-engine, or engine of direct connexion. The first engine of Bell was to some extent a vertical engine, inasmuch as the axis of the cylinder and of the crank were placed in one vertical line; but there was no direct connexion between the crank and the piston-rod to the paddle-axle, the communication of motion to it being effected through the medium of toothed wheels. In the common or lever engine the piston-rod acts on a cross-head, the cross-head on side-rods, the side-rods on side-levers, the lever on a cross-tail, the cross-tail on the connecting rod, the connecting rod on the crank-pin, by which through the axle the paddle-wheels revolve. In the engine of direct communication, the side-levers, and some other parts of the train of communication, are removed by a device which enables the piston-rod to be almost immediately attached by a connecting-rod to the cranks of the paddle-shaft. This plan was first adopted by Mr Gutzmer of Leith, who built a vessel called the Athole, and another called the Tourist, on this principle; but his method, though very simple, was not applicable in ordinary cases; and Mr Napier made se-

Several modifications of the vertical engine, which, according to our judgment, include all the best that have yet been introduced. It does not seem to have been practically established that the engine of direct connexion is preferable to the lever engine; but the plans of Mr Napier appear to have been the best ever adopted.

It is now a considerable time since Mr David Napier relinquished all connexion with such operations on the Clyde; since his retirement, much has been done for the advancement of steam navigation in Britain, and to this work the ship-builders and engineers of the Clyde have contributed their full share. We have already stated that a regular communication by steam was early established between Liverpool and the river Clyde. This establishment has done much for the advancement of steam navigation. It has afforded scope for two extensive companies, who, employing the most eminent steam-engine and ship-builders for the construction of their ships, have produced a very superior class of vessels.

The introduction of wrought-iron hulls for steam vessels, has been the means of introducing a great improvement in the art. This method of construction enables builders to effect a combination of strength and lightness of draught, peculiarly advantageous in some branches of trade and in certain localities. One of the first iron steam-vessels was the Alburkha, of 55 tons. It was built to accompany the Quorra in the expedition to the Niger in 1832, and gave very great satisfaction. The builders of the Alburkha, Messrs Laird of Liverpool, immediately afterwards commenced another vessel, the Garry-Owen, destined to run between Limerick and Kilrush. The length of this vessel was 125 feet on deck, its beam 21 feet 6 inches, and its engines were fifty horse power each. The Garry-Owen was driven on shore, with many other vessels, in the great hurricane which happened about that time, and alone escaped uninjured. This, and other evidence of the power of iron vessels to withstand the casualties of the sea, so raised them in the estimation of builders, that their number was rapidly increased, and their size greatly extended.

For a long period there had been much speculation about the practicability of navigating the Atlantic by steam. So early as 1791, and while the steam-boat was yet in embryo, Fitch, the American, boldly predicted that sailing vessels would soon be superseded in transatlantic navigation. In 1819, an American steam-ship, the Savannah, of 300 tons' burden, arrived at Liverpool direct from the United States, having accomplished the passage in 26 days, partly steaming and partly sailing; and nearly ten years after, the Curaçoa, an English built vessel of 350 tons and 100 horse power, made more than one successful run in the same manner, between Holland and the Dutch West India colonies. Men of science, however, endeavoured to demonstrate that the navigation of the Atlantic by steam-power alone, was the dream of a visionary, and the tide of public opinion seemed to set in in the same belief; but a strong undercurrent was at work, and in 1838 the following advertisement appeared in the daily papers: "Steam to New York. The well-known steam-ship, Sirius, Lieutenant Roberts, R.N., Commander, is intended to leave London for New York on Wednesday 28th March, calling at Cork harbour, and to start from thence on Monday the 2d of April, returning from New York the 1st of May." Thus, a company of merchants was found sanguine enough to disregard the demonstration of the impossibility of an American voyage, and actually to advertise not only the day of sailing, but also the days of arrival and return. The Sirius was not expressly built for transatlantic navigation; she belonged to the St George Steam-Packet Company, and had run with a good repu-

tation between London and Cork. Her tonnage was about 700 tons, and her engine about 320 horse power. Although advertised to sail on March the 28th, circumstances delayed her departure till the morning of the 4th April, when she started at ten o'clock, with 94 passengers. Though first in the race, she was only three days in advance; for on the 7th of the same month, the Great Western, built and fitted expressly for the purpose, followed her. In the interval, between the sailing of these vessels and the reports of their arrivals, much doubt prevailed as to the possibility of their accomplishing their task in safety, and the uncertainty was increased by vessels having arrived from America at ports in Britain, without having encountered either of the steamships; people having, for a moment, forgotten that there were more roads than one across the Atlantic. They were at length, however, spoken with by the Westminster, the Sirius on the 21st, within six hours' sail of New York, and the Great Western on the 22d; and in due time, reports of their having reached New York arrived, the Sirius on the 22d, being 17 days clear on the passage, and the Great Western on the 23d, being 15 days. The Sirius again sailed on her home-ward passage on May 1st, afternoon, and the Great Western on May 7th, and they arrived, the first on the 18th, and the latter on the 22d, being 16 and 14 days respectively. The average speed, and expenditure of fuel of the Great Western was as follows. The whole distance run from Bristol to New York was 3125 miles, averaging each day 208 miles, each hour 8.2 miles; the distance run in returning from New York 3192 miles, each day 213 miles, each hour 9 miles nearly. She departed with 860 tons of coals, and on her arrival at New York she had 205 tons remaining. She left New York with 570 tons of Newcastle coals, and had on board when she arrived at Bristol 178 tons. Her average daily consumption was 27 tons; and, with the expansion valves up, 32 tons. In page 707 there is given a table exhibiting a comparative view of the size and power of six of the largest of the transatlantic vessels.

The practicability of transatlantic navigation being thus fully demonstrated, preparations for its continuance on a gigantic scale commenced, and the British Queen, the President, and other vessels of enormous size, were launched in rapid succession. In addition to these, the offspring of a state of peace, steam war vessels, of great size, are daily constructing, and call for the highest ingenuity of the ship-builders and engineers, in adapting them for taking the advantage of their sails as well as of their steam-paddles.

While the art was thus rapidly advancing, many ingenious men were making attempts to improve the form of the paddle-wheels, or to substitute for them some other impelling apparatus. Of the improvements in the paddle-wheels themselves, we shall have occasion to speak in the sequel. We shall, therefore, in this place, give some account of the most important of the substitutes, the Archimedes screw propeller. The idea of impelling a vessel by means of a screw of a large diameter, lying in the direction of the boat's motion, was originated some considerable time ago; but its first successful application was to a vessel named the Archimedes, constructed under the direction of the patentee of the screw, Mr Smith. From an interesting report of experiments made with this vessel by Captain Chappell, R.N., we condense the following statement:—The burden of the Archimedes is 237 tons, its mean draught of water 9 feet 4 inches. The diameter of the engine cylinder 37 inches, and the length of stroke 3 feet. The screw propeller consists of two half-threads of an 8 feet pitch screw, 5 feet 9 inches in diameter; each is therefore 4 feet in length, and they are set diametrically

Steam Navigation. opposite to each other on the propeller shaft, at an angle of 45 degrees to the shaft. The propeller is placed longitudinally in a hole cut in the dead wood, immediately before the rudder, the keel being continued under the screw. The average performance of the engines is 26 strokes per minute, and the revolutions of the screw in the same time 1383. If there was no slip or recession, the vessel ought to advance 8 feet for every revolution of the screw, or 12.60 miles per hour. The utmost speed ever obtained by her, under the power of steam alone, was 9.25 nautical miles per hour, showing a loss by recession of rather less than $\backslash frac\{1\}\{3\}$th, under the most favourable circumstances. It is necessary to state that the Archimedes is not a fair exemplar of the screw-propelling principle, its steam-power being insufficient to drive a screw adapted to the size of the vessel.

The advantages of this species of propeller appear from Captain Chappell's statement to be these:—1. It occupies a position in the vessel in which it is not liable to injury, and in which it materially augments the power of the helm, enabling the vessel to be turned round and round in circles gradually smaller, until at length it seems to revolve on a pivot. 2. It retains its efficiency of action, even in heavy seas, the rolling, pitching, or lurching of the vessel not materially affecting it. 3. It offers little

obstruction to the speed of the vessel, when the sails alone are employed. When to these are added the saving of expense, which is said to be great, and the removing of the top-weight and unsightly paddle-boxes, we are of opinion that there is enough in its favour to recommend its further trial.

We have now traced the art of steam navigation from its first suggestion to its present state of high perfection. We have overlooked, it is true, much that is interesting in the minute progression of the art; but we have endeavoured to mark its greater advances. We have seen its advancement in the short period of a quarter of a century, from the canal boat experiment of Symington, and the three horse steam-boat of Bell, to the construction of the monster ships, the British Queen and the President, of 500 and 600 horse power. When, in 1820, steamships were first used for conveying merchandise, as well as passengers, the tonnage of the whole of the steam-traders amounted to only 505 tons. In 1821, it amounted to 35,194; in 1822, it had reached to 101,744 tons; and thus advancing, it had arrived, in 1836, at the prodigious amount of 5,429,226 tons. The number of vessels of the mercantile marine, with their power and tonnage, is exhibited in the following table.

An Account of the Approximate Number, Tonnage, and Power of Vessels belonging to the Mercantile Steam Marine of the United Kingdom and its dependencies, at the close of the year 1839.

THE THEORY AND PRACTICE OF MODERN STEAM NAVIGATION.

There is perhaps no popular error more injurious to the welfare of a mechanical nation, like our own, than the notion that theory is opposed to practice; and there is no subject in which this error has ever been more disastrous than in steam navigation, and naval architecture in general. It is by the combination of theory and practice that most is to be accomplished; and it may be hazarded as a general assertion, resting on all past experience, that the best

promoters of the public welfare are—that theoretical man who has made himself best acquainted with the practice of his art, and that practical man who has acquired the greatest knowledge of its scientific principles. There is no art which does not attest this truth, and none attests it more than steam navigation. It is admitted, that out of every three steam vessels that are built, two fall very far short of fulfilling the intention with which they were

Na-constructed. We believe there is no error which it may be possible to commit in steam navigation, that has not already been perpetrated again and again.

To construct a perfect steam-vessel, it is necessary first of all to make a perfect ship; secondly, to construct a perfect steam-engine and boilers of a very complex description; thirdly, to apply a propelling apparatus of the most appropriate description; and finally, to combine all of these in a perfect and well-proportioned whole. Now, to construct a perfect ship, is itself a problem of the highest order, requiring a combination of the most profound resources of analysis, with the highest practical sagacity; a problem on which the reasoning of the mathematician, and the tact of the artist, have long been engaged, with few examples of complete success. To construct a sufficient, effective, powerful, durable, and safe engine and boilers for marine purposes, is a problem more easy, yet one in which there has been encountered continual failure. Then, the means of propelling the vessel over the element on which it floats, give rise to questions in the resistance of fluids which all the resources of hydrodynamic science, in the hands of the ablest mechanical philosophers of the last century, have failed to resolve. Then, last of all, the combination of all of these together, in the best possible way to bring about the precise effect desired, is a problem still more arduous; and all the skill of the analyst, the geometer, the mechanical philosopher, of the naval architect, the engineer, the mechanic, and the sailor, if combined in a single individual, or concentrated on a single object, are not more than sufficient to the arduous task of directing the wealth, enterprise, and resources of this country, in the attempt to render available to her own prosperity, and the interests of the human race, this most admirable of all her creations.

In the following enquiry, we shall soon see that neither practical experience without systematized knowledge, nor superficial theory ignorant of practical wants and practical means, will suffice to ensure success. Both physical science and practical sagacity will, in the art of steam navigation, find enough to exhaust their united resources.

We regret that we cannot record in the present work, that at this day the science of steam navigation is constructed and can be presented to our readers. Even the elementary principles of hydrodynamics are yet to be learned, before we can apply them to the ends of steam navigation. What seems the law of a fluid to-day, to-morrow shows to be a plausible fiction, or doubtful verisimilitude. How then can it be expected that a science should be determined, when its very foundations are yet to be laid? We shall, however, endeavour to generalize what we with certainty know, convinced that a clear statement of our ignorance is often the stepping-stone to truth. The steam-ship consists of three integrant parts: the marine-engine, with its boilers, by which the moving power is furnished; the propelling apparatus, by which it is rendered locomotive; and the ship itself, which contains both. We shall consider each apart, and then their combination.

The Marine Steam-Engine.—The marine steam-engine is of a structure more complex than the common fixed steam-engine, inasmuch as its function is locomotive, and it differs from a land-engine in those peculiarities which adapt it to the unstable nature of its support. He who looks at the ponderous masses of matter that form and sustain the shock of a powerful engine on land, the beams of iron, the blocks of stone, the deep buttresses, and the powerful walls which form its bed, on which it is adjusted at once with the greatest accuracy and power,

and which it nevertheless causes to quiver and tremble Steam Na-vigation. by its giant strokes, will readily understand the incredulity with which the first projectors of steam navigation were regarded.

The earliest application of the steam-engine was to the pumping of water. We find that when it was first used to the effect of making machinery revolve, the great lever of the pumping-engine was retained. So was it in the application of the steam-engine to navigation; and the marine steam-engine, most generally used at the present day, both here and in America, is called the beam-engine, or lever-engine.

The first of the following diagrams represents the beam-engine, or lever-engine, as used on land to turn round machinery; the second represents the lever-engine, as used in America to give revolution to the paddle-wheels of a steam-boat; and the third represents the lever-engine of British steam-vessels.

In all of these figures, S represents the place of the steam-cylinder, in which, by the alternate action of the steam on opposite sides of the piston P, that and the piston-rod P are forced alternately to the top and bottom of the cylinder; and so the end of the lever or great beam B B is carried up and down around the centre M, carrying with it the connecting rod K B', whose reciprocation the crank-pin K, of the crank radius K X, is carried round on the great revolving shaft X; which, in the case of the marine engine, is the axis of the paddle-wheel, and in the case of the stationary engine, is the axis only of the fly-wheel. V is the place of the valves by which steam is admitted from the boiler into the cylinder, and, after having done its duty, is ejected into the condenser C, where, by a jet of cold water constantly playing, it is immediately condensed into water of the seventeen-hundredth part of its bulk, and so leaves the cylinder empty, i. e. nearly a perfect vacuum; and as this condensing receptacle would soon, by the jet of cold water flowing into it, and the accumulation of condensed steam, be filled with water and its evolved gases, the air and water are pumped out at each stroke of the engine by the air-pump A, worked from the lever or working-beam B B, and so the vacuum is kept perfect and the condenser effective. The feed-pump F replenishes the boiler G with some of the water extracted from the condenser, at a temperature of about 90°, and so supplies the deficiency caused by the con-

Steam Navigation. continual evaporation of the water, at the rate of 6 gallons for each horse power every hour.

The differences between the arrangements of the marine steam-engine used in Great Britain, and the land steam-engine, are chiefly these: the lever or great beam, which, in the land-engine, is above the top of the engine, and which in large engines is generally composed of a pair of thin deep beams of cast-iron, united side by side into one; this single beam is brought down in the marine engine to the bottom of the engine, or rather one-half of the great beam is placed on either side of the cylinder, the two being connected together from the opposite sides of the engine, so as to act simultaneously as a single lever. This form of engine, sometimes applied to other purposes as well as to navigation, is called, from this disposition of the working beam, the side lever engine.

Another peculiarity in the marine-engine, sometimes however adopted in land-engines, is the place and arrangement of the condenser C, which, instead of being placed in a cistern of water, is set immediately on the centre of the engine, the condensation being wholly effected by the play of the jet of water in the interior of the condenser, without surrounding its external surface with cold water, as in the stationary engine. When thus placed, the condenser has also the advantage of giving support to the main centre of the engine, around which the levers move in giving revolution to the paddle-wheels.

Before proceeding further with this article, the reader is requested to make himself familiar with the parts and arrangements of the engine already described, by referring to the plates of the marine-engines given at the end, and to the descriptions of them.

It will be observed that the air-pump A is generally placed on the side of the engine furthest from the cylinder. This arrangement is convenient in point of room, and keeps the moving parts of the engine itself more perfectly in equilibrio.

Beside the air-pump is generally placed the feed-pump, designed to force water out of the air-pump or discharge-pipe into the boiler. This is the general disposition of parts, which the reader will easily be able to recognise in the plates given with this article.

Although the lever-engine is the form most commonly employed for marine purposes, it is by no means the only form. Very many attempts have been made to obtain engines more compact and of less weight and bulk than the lever-engine. These are distinguished from the lever-engines by the names vertical engines, steeple-engines, and engines of direct connexion. It is still doubtful whether any of them, except in very peculiar circumstances, are practically to be preferred to the lever-engine; on the contrary, objections of a serious nature are alleged against them.

We have already seen that the first steam-boat, the Comet of Mr Bell, had a vertical engine. It was remarked of this vessel that the strain of the engine on the vessel was very small; but this has been attributed to the low proportion of power to the tonnage of the vessel.

The first steam-vessel whose engines we had the pleasure of seeing, had a pair of vertical engines, made by Gutzmer of Leith; the paddle-shaft B being directly over the axis of the cylinders A, as in figs. 4. and 5.

Modifications of this plan of direct or imme-

diate connexion have been recently tried on a larger scale; but the method has the disadvantages of admitting only a short stroke and a short connecting rod, and requires that the height of the axis above the bottom of the cylinder should be at least three times the length of the stroke. Thus, one of the extremes, too short a connecting rod, too short a stroke, or a paddle-axis too high above the floor of the vessel, is incurred.

To obtain the same object without incurring those evils, many descriptions of engine have been contrived. The following admits of placing the paddle-axis at little more than double the height of the stroke of the engine, and gives a connecting rod of $1\backslash frac\{1\}\{2\}$ or 2 times the stroke. The piston-rod P is inserted into a cross-head d d, to the extremities of which two vertical rods d e, d e, are attached. With the lower extremities of these rods the side-rods g f, g f, are connected; the upper ends of these side-rods are attached to the cross-head g g, to the centre of which the crank-rod is attached.

This species of engine has the great disadvantages of a multiplicity of shafts, bearings, and cranks. It was afterwards simplified by Mr David Napier in the manner represented in the following figures; viz. by uniting into one forked cross-head each cross-head with its side-rods.

Even thus, however, limits are placed on the length of stroke and height of shaft, so as to give rise to inconvenience in many circumstances. To remedy these evils, Mr Napier appears to have invented the following class of engines, to which the cant term of steeple-engine appears to be sufficiently appropriate. In the steeple-engine the piston-rod is made forked or divaricated, so as, passing round the shaft, to rise above it to a considerable height, from which again descends the connecting rod to the crank. The following example is that

of the engine of a vessel named the Clyde, the first of the kind we ever saw:—

The top of the piston-rod carries a quadripartite cross-head $h\; h$, on each end of which stands a pillar $h\; h$; these four pillars again unite in another quadruple cross-head, sustained upright by a vertical guide; and it is from this summit that a connecting rod descends to the crank $k$. We believe that this principle of continuing the piston-rod round the axis by a forked frame was first devised, at the end of the last century, by Trevithick, the famous high-pressure engineer, and by him applied to steam-carriages. It is drawn in his patent specifications.

After passing through a great variety of phases, the steeple-engine appears to have settled down into the two following shapes. In figs. 14 and 15, the piston-rod is seen united to a triangular frame, from the apex of which the connecting rod descends to the crank. In fig. 16, this frame is shown to be square, and fig. 13 is the side view of both varieties.

Another method of accomplishing the direct connection without encumbering the deck, has twice been patented: in the last instance by Mr Humphreys. It may

be called the trunk-engine. The axis is placed at the height of half the stroke, or more, above the cylinder, and a connecting rod unites immediately the crank-pin with the centre of the piston.

In this way the connecting rod, passing through the top of the cylinder, would allow the steam to escape but for a large trunk or casing with which it is surrounded, and which, passing through a chasm of large area conceived to be steam-tight, rises and falls with the piston to which it is attached. In fig. 17, $A\; A$ is the cylinder: to its piston is attached a trunk $B$, which works through a stuffing-box in the cylinder cover; to the piston the connecting rod $c\; c$ is attached. Fig. 18 represents the top of the cylinder $A\; A$, with its stuffing-box and the trunk $B$.

For a like purpose, oscillating cylinders have been used with some measure of success. Rotatory engines have been unsuccessfully tried. The reader may now examine the vertical engines in the plates.

In short, it does not appear that any vessel, either on a large or small scale, constructed with an engine different from the ordinary side lever engine, has been found to be practically superior to it; and therefore we shall for the future speak of the lever-engine of the ordinary construction, when we treat of the marine steam-engine, unless when another species is expressly mentioned. The lever-engine possesses three advantages of an important nature:—first, its parts are nearly in equilibrio; secondly, its basis embraces a large part of the vessel's bottom for strength; thirdly, the lever presents great facility for working its appendages.

The Cylinder of the Marine Steam-Engine.—The cylinder of the steam-engine being that portion of its apparatus, by means of which the elastic force of the steam engine is directly applied to the mechanical arrangements by which the force of the machine is developed, is therefore the principal member of the engine, on the size of which its powers and the dimensions of the other parts depend.

It is according to the dimensions of the cylinder that an engine receives its denomination, and is bought or sold. An engine is called a 10, 20, 50, or 100 horse-power engine, according to the number of inches in the diameter of the cylinder. It is not to be expected, however, that every steam-engine will develop the power of a given number of horses, simply because it has a cylinder of a given number of inches. This depends equally on the proper proportion, construction, and condition of all the other parts, without which the engine will be incapable of doing its proper duty. The engines of some makers will develop double the power of those made by inferior engineers, even although in name and dimensions identical. Hence, the dimension of cylinder is taken according to a rule somewhat arbitrary, of the value both dynamical and pecuniary of the engine under the term nominal power; and the actual efficiency of the engine under given circumstances, is called the real or effective power. Hence an ambiguity is incurred in speaking of the relative powers of engines, when it is not determined whether the real or nominal power is referred to. An engine of 100 horse power, which ought to be capable of giving out an effective power of 100 horses, may, from bad workmanship, bad arrangements, or modified circumstances, only give out the real power of 50 horses; and an engine of the same dimension of

Steam Navigation. cylinder, and of the same nominal power, but of better construction, may give out, and frequently does give out, real and effective power equal to that of 150 horses. Real or effective power, and nominal or mercantile power, are seldom identical, and should always be distinguished from each other.

Even the nominal or mercantile standard of power is not so perfectly invariable as may be desired. It varies a few inches according to the practice or policy of the engineer, who is frequently called upon to give an inch or two more in his mercantile dimensions, than the strict letter of his agreement might demand. Another cause of variation is this, that some engineers will prefer to sell a larger actual dimension under the name of a less number of horse power, that their engines of a given nominal power may apparently do more work than those of other people. It is a third cause of variation, that some engine-makers give more than the actual dimension belonging to the power, in order that, under even the most unfavourable circumstances, the possessors of the engine may derive from it more than the full measure of the actual effective power which they require.

The following table has been constructed from a comparison of the practice of the most eminent marine steam-engine makers, with the principles of their construction. But under the dimensions given, the engines of best construction will give out from one-fourth to one-third more than their nominal power. We know, for example, that a cylinder of 74 inches diameter has been constructed under the designation of 200 horses, whereas its proper nominal power is above 225 horses, and its actual effective power, as given out in the ship, was more than 300 horses. The contraction H.P. is generally used instead of the words horse power.

Table of the Dimensions of the Cylinder of a Marine Steam-Engine of given Horse power.

This table shows that the power of the steam-engine increases more rapidly than the area of the cylinder or the square of the diameter. By the rule of the square of the diameter, the power of an engine of 74 inches would be about 200 instead of about 225; and 100 inches diameter would give only 333 horse power; but the same rule would give too small a diameter for the lower powers. We believe that engines of the dimensions of this table will all work to more than their nominal power.

The best proportion between the diameter of the cylinder and the length of the stroke, has been the subject of much dispute, and of opposite practice. In America, a diameter of 40 inches is sometimes combined with a stroke of 10 or 11 feet, being more than double the length given in this country. On the Clyde, we have seen the opposite extreme, a diameter of 60 inches with a stroke of only 4 feet. For sea-going ships, the proportions we have given are the most convenient. In deviating from this proportion, a longer stroke will be preferable to a shorter; and with the necessary alterations required for high velocities of piston, a longer stroke working the steam expansively is likely to be attended with many advantages.

By means of a long stroke or great velocity of piston, considerable advantages are gained. The pressure upon the journals and working parts of the engine, and the consequent strain, is lessened in proportion to a given power. All the parts of the engine might be lighter than with a shorter stroke and a greater diameter of cylinder. A short stroke has however this advantage, that with a given length of lever and connecting rod, the angles of oblique pressure are smaller, and the intervals of time between maximum and minimum pressure are shorter. There are other peculiarities of smaller importance. On the whole, a longer stroke than that of the present British engine, as given in the table, is to be reckoned considerably preferable to a shorter one.

The velocity of the piston in the cylinder of a steam-engine is generally reckoned in this country at 220 feet a minute, and all the arrangements of the engine and its work are made on that principle. We can find no better reason for this than that a horse going at that speed, viz. two miles an hour, can draw 150 lbs. eight hours a-day, all the year round. Tredgold finds it to be a law of nature. It is strange how much this arbitrary dogma, transmitted without question, has retarded the improvement of steam navigation. It is a rule as universal in its acceptance as it is groundless and injurious. With large condensers, and large ports and valves, double the speed may be employed with great advantage.

The Condenser and Air-Pump.—The condenser is the most wonderful part of the marine-engine, as indeed of the ordinary steam-engine. It is here that the whole process carried on in the boiler in so great bulk, and at so much expense, is instantly reversed, and all its laborious effects at once, as it were, annihilated. It is the instantaneous condensation that is its virtue: without this the whole of its virtue in the steam-engine is lost. Suppose a condenser capable of condensing the steam as fast as it is generated by the boiler, and given off in the cylinder, and no faster, what would be the consequence? The power of the engine would cease, the elastic force of the steam above the atmosphere would alone act, the steam being only condensed as the piston carried it out of the cylinder; the engine would become nothing else in power but a high-pressure engine, whose steam is merely condensed before going out into the atmosphere. It is by forming a perfect vacuum in the

cylinder on the moment when the steam is about to enter on the opposite side, that the full power of the steam can alone be obtained in useful effect. A perfect condenser must, therefore, have much greater capability than that of merely condensing the steam as fast as the boiler is capable of evacuating it, or the engine of passing it through.

We have insisted the more strongly on this point, inasmuch as it is here principally that power is to be gained at smallest expense. Many other modes of condensation have been tried besides condensation by jet, and without effect. Newcomen tried to condense by cold water outside his condenser; so did Savary, so did Watt, so did Cartwright, so did Napier on the Clyde, so did Stevens of Hoboken in America, so did Trevithick, Symington, Mills, and many others; but without success: for though they all succeeded so far as, by having cold water on the outside of the vessels, to condense the steam in the inside, yet this condensation by contact, however perfect in quantity, has always been slower in time than condensation by jet, and has consequently failed in developing the full power of the engine. In this list we have not mentioned the name of the ingenious and enterprising Mr Hall of Basford, as he still continues to persevere against the difficulty of introducing successfully into use the system which has baffled the efforts of his predecessors; and perhaps his attempt may be attended with a higher degree of success than theirs.

It appears difficult to assign a volume to the condenser which shall give it most efficiency. We have seen efficient condensers from one-fourth of the volume of the cylinder up to its full size. One-half the volume of the cylinder appears to be a size sufficiently convenient and effective.

The proper distribution of the water forming the jet, throughout the whole volume of the condenser, seems the most important point of efficacy in the condenser. Some engineers accomplish this by allowing the water to rise from the bottom of the condenser in a jet d'eau, which striking the top, falls down in a shower, filling the whole condenser; others make this shower radiate in all directions from a perforated horizontal pipe; and a third most effective method is, to spread out the jet in a thin film or sheet, like a waterfall, through which the steam is compelled to pass. In marine engines, the water is permitted to flow into the condenser through a pipe in the ship's side, regulated by a cock.

Much has been said regarding the perfection of the vacuum found in the condenser of a steam-engine, especially a marine engine. It does not appear to be known that a vacuum may be too good. We hear it boasted every day by rival engineers that their engines have the best vacuum. Some boast their vacuum at 27 inches, others at 28, others at 29, some at 30, and at last an engineer appears who boasts a vacuum of 30½ inches. It is to be regretted that time and talent should be thus wasted. It is a fact of great importance, confirmed by experiment and by practice, that a vacuum may be too good, and become a loss instead of a gain. The truth is simply this, and should be known to every engineer: If the barometer stand at 29½ inches, the standard of this country, the vacuum in the condenser is too good if it raise in the barometer more than 28 inches of mercury. This important truth is incontrovertible, and is practically exhibited every day.

The following is a simple proof of this doctrine, dressed as far as possible of a technical form, and put in the shape of an enquiry into the best state of a condenser.

Let $t$ = the caloric of water of 1°.

$c$ = the constituent caloric of water in the state of steam.

$e$ = the total force of steam in the boiler in inches of mercury;

and $x$ = the elastic force of steam at the temperature of best condensation which we seek to discover.

Then from the law which connects the elastic force of steam with temperature, as already determined in the article STEAM, it follows, that in the case of maximum effect, or the temperature of best condensation,

now $e\; =\; 1000$, and if the steam in the boiler be at 5 lbs. above the atmosphere, or if $e\; =\; 40$ inches of mercury, and $t\; =\; 1$,

Again, if the steam be at 7½ lbs. = 45 inches,

Again, if the steam be at 10 lbs. = 50 inches,

Hence, we find that the best elasticity or temperature in the condenser depends on the elastic force of the steam in the boiler.

With steam of 5 lbs. in the boiler, the elasticity of maximum effect in the condenser is at 93° of Fahrenheit, and the best vacuum in the barometer is 28. With steam of 7½ lbs. in the boiler, the elasticity of maximum effect in the condenser is 95° of Fahrenheit, and the best vacuum in the barometer is 27.8. With steam of 10 lbs. in the boiler, the elasticity of maximum effect in the condenser is 97°, and the best vacuum in the barometer is 27.5. In like manner it would be found that with steam of 50 lbs. in the boiler, worked expansively, as in Cornwall, the best vacuum in the condenser would be about 26° on the barometer.

It is hoped, therefore, that engineers will not in future distress themselves, at finding the vacuum of their condenser much less perfect than the vacuum of others who have obtained 30, and 30½ inches, at so great a loss of fuel and power. To obtain a vacuum of 29½ with the weather-glass at 29.75, and steam at 7½ lbs., would be to sacrifice four horse power out of every hundred. In a day when the barometer is as low as 28½ inches, the vacuum in the condenser should indicate 26.8.

In speaking of the vacuum in the condenser, it would save much ambiguity to indicate the elasticity merely of the gas in the condenser. Thus, if the barometer stands without at 29½, and the barometer of the condenser at 28, it might be stated that the steam in the condenser stands at 1½, being the point of maximum effect; and the indication would at all times convey more precise information.

An air-pump is an appendage rendered necessary by Air-pump the condenser, and especially by condensation by jet of marine d'eau. Ordinary water contains about 5 per cent. of air and other gases, which become disengaged in the condenser, and must be withdrawn, to maintain the vacuum. Hence the air-pump, which is also used to withdraw the water which accumulates in the condenser. A valve between it and the condenser is called the foot valve; and a valve at the exit from the top of the air-pump is called the discharge valve. They are thus arranged: S the cylinder, C the condenser, A the air-pump, F the foot valve, and D the discharge valve.

The dimensions of the air-pump seem to vary much, from $\backslash frac\{1\}\{2\}$ to $\backslash frac\{1\}\{3\}$ of the volume of the steam-cylinder. I do not know any disadvantage of importance in having a large air-pump; as, if properly constructed, the force which is required to work it will be nearly in the proportion of the elasticity of the gas which it has to remove from the condenser. To give the air-pump half the stroke of the cylinder and $\backslash frac\{1\}\{2\}$ of the area of the cylinder, or $\backslash frac\{1\}\{4\}$ of the stroke of the cylinder and $\backslash frac\{1\}\{2\}$ the area of the cylinder, are common proportions.

The Valves and Valve Passages.—The notion that because a horse can do most work at the rate of 2$\backslash frac\{1\}\{2\}$ miles an hour, or 220 feet a minute, therefore a steam-engine should also move at that rate, is a prescriptive error almost ridiculous; but from which it will nevertheless be difficult for us to escape, especially as the proportions generally in use are derived from this absurd dogma. There is no doubt that the passages and valves should simply be as large as possible, and those valves should be used which can be most enlarged with least inconvenience. Such valves we possess in the class of equilibrium valves. These valves may have an area as large as the tenth-part of the cylinder without disadvantage, and the velocity of the piston may thus be increased, and consequently the power of the engine, with great advantage, especially in steam navigation. We have the best possible means of knowing, that with proper valves and passages, the speed of the piston may very advantageously be increased to 250, 300, 400, and 500 feet a minute. The pistons of the swiftest vessels in the world move at that rate.

The kind of valve most commonly in use in steam-vessels is the long D-slide, as it is called; and next to that is the short D-slide. There are scarcely any other kinds in use in Britain. A valve called the four-port slide valve has been used to a limited extent, as have also conical valves, and equilibrium valves, or double heat valves in this country, the latter very extensively in America. The following are diagrams of the long and short D-slides.

The four-port slide valve is a recent invention, having been the subject of a patent so lately as 1833. Since that time they have been used to a considerable extent in one part of Scotland. The same kind of valve was subsequently patented by another party in England, and port these valves were put on board of some of her Majesty's frigates. The following figures represent the four-port slide valve, in two positions. A the cylinder; pp the piston; S the steam-pipe; VVVV the slide valves. The arrows show the direction of the steam.

The equilibrium valve has already been described in the article STEAM-ENGINE.

The size of the valves is a matter of some consequence. That the valves, passages, and ports by which the steam enters the cylinder should allow a free passage of $\backslash frac\{1\}\{2\}$ of the area of the cylinder, is an old and pretty general rule. It is equally certain, however, that the eduction valves, ports, and passages by which the steam enters the condenser should be much larger. They have been made $\backslash frac\{1\}\{2\}$th and $\backslash frac\{1\}\{3\}$th of the area of the cylinder with advantage, in the case of high velocity of the piston.

The Eccentric.—The valves, by means of which the steam is alternately admitted to the cylinder on one side, and educted from the other side, into the condenser, are moved by the machine itself; and the very simple and beautiful automatic contrivance for that purpose is called the eccentric.

We have already described the actions of the eccentric in the article STEAM-ENGINE. In the marine engine it is placed on the axis of the paddle wheels. In engines fig. 24 its usual arrangement is shown, and in the Plates many examples will be found.

As the shaft A moves round, it is plain that the projection of the eccentric, first on one side of the shaft and then on the other side, will draw the eccentric rod in opposite directions; and the distance of the centre of the eccentric from the centre of the shaft, will be placed now on one side and now on another side of the axis. The motion thus produced is called the throw of the eccentric; and half the throw is equal to the eccentricity.

An important point in setting the valves is what is called the lead on the centres. What is the best instant of time at which to allow the steam to enter or escape from the cylinder? At first sight we should say, precisely at the instant of reversing the direction of the motion. This is not the case. Great advantage is gained by letting the steam out of the condenser before the end of the stroke. A little of the force of the steam in the cylinder may thus be sacrificed; but it is a very little, say $\backslash frac\{1\}\{50\}$th of the stroke, and is much more than compensated by this, that the steam escaping thus early into the condenser, time is allowed for effectual condensation, and there is an excellent vacuum in the cylinder by the time when the back-stroke begins. In like manner, the steam-port may be slightly opened before the engine comes to the centre; and as there are vacuities at the top of the cylinders to be filled, and as time is wanting for the passage of the steam, this is allowed. By the same means also the steam is cut off a little before coming to the end of the stroke, which allows the engine to work expansively; and the vacuum port may in like manner be shut, as the vapour will have been perfectly condensed in the cylinder long before the end of the stroke. Much of the efficiency of an engine depends on the adjustment of the slide.

The eccentric of the marine engine is generally a loose eccentric, capable of turning the valves either so as to give the engine motion forwards or backwards. By placing the eccentric loose upon the axis, only with a projection on one side, which is carried round by a corresponding projection on the axis, it is left free, except when this check comes in contact with the projection at either end of the stroke. To effect this, it is necessary to open the valves by hand through at least one half-stroke.

The Hand-Gear.—The hand-gear is generally a lever or series of levers, which enables the engineer to shut and open the valves by hand before placing them in connexion with the eccentric. By this means he places the machine either in the condition to keep moving forwards or backwards. For examples see the Plates.

The Expansive Valves.—It is of advantage to cut off a part of the steam which would be required to fill the cylinder, so as to allow that quantity which has partly filled it to expand with its elastic force, and fill the rest of the cylinder without further supply from the boiler. The advantage of doing this, especially in long voyages, has now become pretty generally known. A stop-

valve V, fig. 25, is placed on the steam-pipe S S, before it joins the casing of the common valves, which are applied as usual. The principal axis A of the engine carries a cam, with two projections a and b proportioned in breadth to the extent of

the stroke which is cut off. On this cam rolls a small pulley b, pressed close by a weight w; and by a simple connecting rod the cam opens and shuts the valve with great velocity twice in each revolution. On this cam there may be various grades at which the steam may be cut off in the stroke of the engine. This apparatus is used in all vessels calculated for long voyages.

The Proportion of Power to Tonnage.—Large power

or small power has always been one of the verate ques- Steam Na-
tiones of steam navigation. The early steam-boat en-
gines had but a small power proportioned to the ton-
nage of the vessels in which they were placed. The Proper-
Comet had 25 tons burden and only three horse power, tion of
being about one horse power to eight tons, or a pro-
portion of power to tonnage amounting to one-eighth. power to
tonnage.

On this subject modern practice and modern opinion seem to offer no guide. A low proportion of power and a high proportion of power have both their advocates. The East India Company have advocated and used low proportions of power to tonnage, and in this they appear to have followed the general maxims of southern engineers. The Government also appears to have adopted the same course; but without going to the same extreme. The Clyde engineers adopt the opposite maxim, and place as much power in their vessels as can be conveniently applied. There appears at the present moment to be a strong feeling in favour of a high proportion of power to tonnage. It has been found by some of the best mercantile companies, that a high proportion is not only better for expedition, but also more economical of fuel and of capital than a smaller proportion; and instances are frequent of an increase in the power of a steam-vessel, producing a diminution in the consumption of fuel.

As this question is becoming every day of greater importance, it is proper to examine it carefully. In the first place, it is well known that the proportion of power must be very much increased to gain a given increase of speed. Thus, if 120 horse power propel a vessel through water five miles an hour, it will require forty horse-power to propel the same vessel ten miles an hour, or it will require a quadruple power to obtain a double speed; and, in like manner, it will require a ninefold power to triple the speed. In fact, the increased speed requires an increased power in a duplicate ratio of the increased speed; or if the speeds be as the numbers 1, 2, 3, 4, 5, 9, 10, &c., the power required to attain those speeds must be 1, 4, 9, 15, 25, 81, 100 horses; or according to the well known law of the resistance of fluids, the resistance which the water opposes to increased speed is nearly in the duplicate proportion of the speed. Thus, to increase the speed in a given proportion, the fire of the engine and the consumption of fuel, which is nearly as the power of the engine, must be increased in a very high proportion. Hence the seeming great economy of a low power of engine and a small consumption of fuel.

Thus a large power of engine occupies much of the useful space of the vessel, which might have been filled with cargo. It consumes much coal, and the speed is by no means proportioned to the expense of fuel and machinery. But this is a very limited view of the subject. If time as an element, and a very important one in the value of mercantile conveyance, be calculated, then it will in many cases be found, that high speed at any expense of fuel will compensate for that expense. This is the case to a great extent in Britain, and especially in America, where a quarter of a mile an hour between the speed of two vessels ruins the fortune of one owner, and makes the fortune of another. But it is not on the value of speed at the present day, that we proceed in this enquiry; that can at once be appreciated by the local peculiarities of a given case. We are to enquire what may be the best proportion of power to tonnage in sea-going vessels, apart from the mere price of speed in the market.

We have seen that the lowest speed in a steam-vessel is the most economical, and that it requires great and expensive additions of power to gain high velocities.

But in arriving at this conclusion, we have taken only the case of smooth and still water. Here it is obvious that the slowest rate and smallest power will be most economical; but it should be remembered that the great purposes of steam are generally of a different nature from the mere generation of motion through a quiescent fluid. The force of adverse winds and waves is to be opposed, stream-tides and currents are to be stemmed; and it is the success of steam in conquering those obstacles, and obtaining regularity and speed in spite of them, which constitutes its superiority over wind or animal power in navigation.

Now, if we take a simple case of one of these, we shall soon find that a higher proportion of power to tonnage may be essential, not only to speed, but even to economy. Suppose a steam-boat with a small proportion of power, capable of propelling the vessel at the velocity of three miles an hour through still water, to be applied to stem a current of three miles an hour, is it not plain that the vessel would make no head way, and thus a low proportion of power would burn an immense quantity of coal in doing nothing but standing still?

Let us again suppose that the same vessel, capable of steaming three miles an hour, meets with a moderately strong breeze opposed to her, such as prevents her from making any progress at all against it; then it is plain that by the continuation of this breeze, the vessel burning a continual supply of fuel would consume an indefinite quantity of coal in standing still. This extreme case of too little power, shows that there is at least one proportion of power, which is too small for economy of fuel; viz., that proportion which, being very economical of fuel in fine weather, is brought up altogether by adverse winds. In this case, the consumption of fuel is rendered indefinite, and the useful effect of fuel completely annihilated by too small a proportion of power.

As, then, we have plainly established the existence of a limit to diminution of power, in the vicinity of which it must be followed by extravagant consumption of fuel, we may now proceed to investigate the question of best proportion, or the point where the attainment of high speed is accompanied by absolute saving of fuel as compared to lower velocity. For this purpose, we merely take it for granted that the speed through the water will be nearly as the square root of the power, according to the general law of the resistance of fluids; that the resistance offered by bad weather or adverse winds has been ascertained and is determined on a particular station; that is, that it is known that on a given station a given vessel with a given power makes a voyage in adverse circumstances in, suppose, double the time of her most prosperous voyage; say her most prosperous voyage is in fourteen days, and her adverse voyage in twenty-four days, being a retarding power of ten days out of twenty-four; we take this retardation of ten days as the measure of the retarding power of adverse weather in the given circumstances. And further, let the following quantities be thus represented:—

Also, let $k$ represent the consumption of fuel per horse-power per hour, and $s$ the length of the voyage or distance performed. Then

Putting $f\text{'}\text{'}\text{'}\; =\; u$, $h\text{'}\text{'}\text{'}\; =\; x$, and differentiating, we get

whence by reduction, in the case of a minimum, we obtain the value

Whence we obtain the very simple rule for finding the best proportion of power to tonnage: From the square of the velocity of any given vessel in good weather, subtract the square of the velocity of the same vessel in the worst weather, divide the difference by the square of the velocity in good weather, and the quotient multiplied into double the horse-power of the said vessel will give the power which would propel the same vessel in the same circumstances with the smallest quantity of fuel.

It appears from the comparison of (B) with (C), that a vessel has its power in the most economical proportion to its tonnage on a given station, when its worst voyage does not exceed the time of its best in a greater proportion than $\backslash sqrt\{2\}$ to 1; that is, than 14 to 10, or 7 to 5.

From (D) and (E) it further appears that in a vessel, whose power is thus proportioned, the consumption of fuel in the worst voyage will not exceed that of the best voyage in a greater proportion than 10 to 7; that is to say, for 70 tons of fuel burned on a good voyage, it will not be necessary to carry more than 100 tons, in order to provide against the worst.

Let us take as an example a transatlantic steam-ship, which has a proportion of 1 horse power to 4 tons of capacity. Her unfavourable voyage being between England and America twenty-two days, and her favourable voyage fourteen days, being a comparative velocity of 7 and 11, then

Hence, the power of such a vessel should be increased in the ratio of six to five; that is to say, the engines at

present capable of exerting a power of 500 horses, should have been capable of exerting a power of 600 horses, and would in this case have consumed less fuel, as well as have produced greater regularity and a higher velocity.

The following results are obtained:—

The vessel of less power burns thirty tons per day, performs the distance in fourteen days, consuming 420 tons of coals in fair weather.

The vessel of less power burns thirty tons per day, performs the distance in twenty-two days, consuming 660 tons of coals, in foul weather.

The vessel of greater power burns thirty-six tons per day, performs the distance in twelve and one-half days, consuming 468 tons of coals, in fair weather.

The vessel of greater power burns thirty-six tons per day, performs the distance in seventeen days, consuming 630 tons of coals, in foul weather; being a consumption of sixty-four tons less fuel, and performing the voyage in four and a half days less than the other.

It is manifest that the store of fuel carried in the vessel with less power, must on all occasions be equal to the greatest consumption of fuel, that is, to at least 660 tons, whereas 630 tons will be sufficient for the vessel of greater power; and as in all vessels for long voyages, coals carried are much more costly than the mere price of coals, or as the freight of the vessel is more costly than the fuel, coals carried are to be reckoned at least as expensive as coals burned. Moreover, as the gain in time and in capital is four one-half out of twenty-two, being twenty-five per cent, it is plain that the vessel may be calculated to perform the distance oftener in a year; because as the times of starting must always be regulated, not by the shorter but by the longest period of a voyage, seventeen one-half days in the one case, stand in the place of twenty-two days in the other.

As another example, let us take the case of a vessel calculated to stem the monsoon in the Indian seas. A vessel of 600 tons and 200 horse power, steaming in fair weather at the rate of eleven miles an hour, has been found to have her speed diminished by the monsoon to five miles an hour. What would be the best proportion of power in such circumstances?

Hence we see that the power being increased in the ratio of sixteen to ten, that is, engines of 320 horse-power being substituted for those of 200, the speed on the quick voyage would be twelve three-fourths miles an hour, instead of eleven, the speed against the monsoon increased from five to nine miles an hour, with a saving of coals amounting to forty tons out of 320; and when it is remembered that the voyage for which eighteen days would be required as continual allowance in the one case, might always be calculated on as performed in ten days in the other, the advantage is placed beyond all doubt. It appears, therefore, that for long voyages especially, great advantages in point of economy, certainty, and speed, are to be obtained by the use of vessels of a higher power than usual; and that, in a given case, the best proportion of power to tonnage may readily be determined from the rules already given.

In regard to absolute or definite proportion, it may be stated as the result of the best vessels, that the proportion of power to tonnage should not be greater than one horse power to two tons: the greater proportion holding in the smaller, and the less proportion of power in the greater vessel.

The Proportions, Form, and Mechanical Structure of Steam-Ships.—In the article SHIPBUILDING, the reader

will find the elements of construction of ships developed and applied in a satisfactory and lucid manner. There he will also learn, that naval architecture is scarcely recognised as a science in England. The reader will therefore be prepared for the announcement that the proportions and structure of steam-vessels is an enquiry which has hardly as yet systematically commenced; and it is with much hesitation that we set the example of endeavouring to eliminate from the rude mass of practical truth and practical error, some general results worthy of confidence. We may premise, that the drawing and finding the displacement, centres of gravity, and buoyancy, and the calculations of stability, &c., may be performed for steam-ships by the methods, and on the principles developed in the article to which the reader has already been referred.

The proportions of steam-vessels were originally taken from sailing vessels; the length being three or four times the breadth. Six breadths to the length is now a common proportion. The proportion of depth varies with dimension, being about one-half the breadth in vessels of 100 tons, two-thirds of the breadth in vessels of about 600 tons, and three-fourths of the breadth in vessels of 1500 tons. The qualities of a vessel depending much on its form, it is not possible to deduce a very precise rule for proportion abstracted from shape; but the following list of dimensions is deduced from a comparison of the dimensions of the best vessels, and will serve as a standard of reference for the existing state of practice. The following are dimensions of flush-decked vessels without poops or forecastle. Where these exist, the depth must be diminished so as to leave the mean depth the same. Thus, in the table, a vessel of 180 feet long by thirty feet beam, has twenty feet depth; but with a half-poop she would require to be only about eighteen one-half feet deep.

Table of Dimensions of Sea-going Steam-Vessels of the best proportions, in conformity with the best practice in Britain.

The form of the ship, of course, affects very materially its qualities, and the choice of proportions to produce those qualities. The dimensions in this table apply to vessels of fine proportions, having a fine entrance and run, and a side nearly upright. If however the area of the load-water line be very large, the vessel will be uneasy even with these extreme dimensions; and in such a case the beam in the table is rather excessive, while the height might probably be augmented without inconvenience. Again, if the midship section of the vessel be very square, or merely rectangular, these dimensions will suffice. If however the bilges be round, and the sides slope outwards, more breadth may be usefully employed, so as to leave the breadth at the load-water line nearly equal to, or rather greater than, the beam given in the table.

River steam-vessels are, in this country, and especially on the Thames, made of great length in proportion to beam. Some of the swiftest river boats have their length equal to seven, eight, nine, and even ten times their beam, with advantage. In America they often have twelve times more length than breadth.

The Form of Steam-Vessels.—To determine the best form of a steam-ship may appear to be a much simpler case of the great problem of naval construction, than the formation of a sailing vessel. The principal desideratum in a steam-ship being the power of going fast through the water in the single direction of the propelling power, this case of the problem appears to approach much more closely to the construction of a solid that shall receive the least resistance in passing through the water, than to the case of the sailing vessel, which has to work with a propelling power which is generally in some other direction than that in which the vessel is designed to make way. In this point of view, the problem of the steam-ship is really a simpler case of the general problem than that of the sailing vessel. If, however, the steam-ship is also to be a good sea boat, and to work on some occasions under canvass alone, as well as under steam alone at other times, the problem at once assumes an aspect more complex than that of either problem taken by itself.

There is, however, a single fact which is important, as it very much simplifies the subject. Vessels built expressly for the purpose of steaming, and adapted for that purpose in the best possible way, have been found, when under canvass, to equal the fastest ships in sailing qualities. Their great length and fine ends prevent them from falling to leeward; their fast formation adapts them for going through the water; their boilers and machinery form a well placed and well distributed ballast; their fine ends and flaring bows render them lively as sea boats; and the small amount of their midship section, and small resistance, give them great speed under comparatively little canvass. This practical fact, that a vessel formed exclusively for steaming, and adapted for that alone, in the best possible manner, is found to be a good and fast ship under canvass, greatly facilitates the enquiry concerning the best form of a steam-ship. To this we now add another confirmatory fact, that the fastest schooners, cutters, smugglers, yachts, and slavers, approach more nearly to the form of the best steamers than any other class of sailing vessels. The problem of the best form of a steam-ship becomes thus not only simpler, but doubly interesting, from the reflex influence it may be expected to produce on sailing ships.

It is difficult, without going into minute technical details, to explain the peculiarities in the shape of the best steam-ships. The present state of practice shows that systems perfectly opposite are adopted by different builders. It is at all times difficult to convert into ver-

bal statistics forms so delicate and complex as the surfaces of double curvature formed by the bottom of a ship; but the following considerations of a general nature may probably be intelligible.

In the formation of steam-ships, it has been stated that there are opposite schools. One adopts and advocates a sharp bottom, a great rise of floor, great beam, extensive bearings on the surface, round sides, round water-lines, adopting altogether the formation of a full, capacious, stable, sea-going ship, only employing such dimensions and proportions as are given in the table of dimensions already produced. Another school adopts a flat bottom, long floor, more angular bilge, upright sides, straight entrance, clean run, sharp ends, comparatively small moment of stability, formed with the idea of going directly through the water in all weathers with the least proportion of resistance, and the smallest change of position. A third school, of recent origin, adopts the hollow wave lines and new formation, of which the principles have been established by the writer of this article. The fastest steam-vessels of the present day are built on this principle.

The question of form may be taken up under several heads.

The Transverse Section, or Midships.—The simplest Midship and one of the earliest sections of a steam-vessel is the rectangle, fig. 26. the bottom being flat, the sides vertical, and the bilges almost angular. This form is rendered necessary when the breadth of the vessel over the paddles is to be rendered as small as possible. But this form, although it gives the greatest capacity when the breadth and depth of water are limited, is at once weak at the bilges, liable to crankness, and uneasy at sea. To remedy these evils, the bilges have been rounded, and the floor sharpened, in order to give more easy lines on the bottom, and an easier bilge, as in fig. 27.

And again, this method has been carried to an extreme, or with the intention of producing the best possible sea boat, by making the floor very sharp, and the sides extremely round, thus:

But such boats are both unstable at sea, and pitch most violently. The next modes of construction have had for their object to produce the greatest capacity with the least material, and least surface of adhesion to the water. For this purpose semicircular and elliptical bottoms have been tried, thus:

But both of these, and especially the former, although well suited for fast steamers, have a great tendency to oscillate continually, and roll with great latitude at sea.

It appears from experience, that there is great difficulty in determining that section of vessel best suited to a steam-vessel. The rectangular figure first given is, as we have said, at once weak, and crank, and uneasy. The sharpening of the bottom, as in the figures which follow it, removes the engines up from the floor, and effectively diminishes the height of the engine-room, as well as renders the vessel crank, by raising the centre of weight, and of the engines, &c., too high; and if, to counteract this evil, the beam at the surface of the water be increased as in the third section, the vessel is rendered laborious, uneasy, and ineffective at sea by the excessive beam. Again, in the round bilges the vessel swings like a pendulum, and it seems as if her oscillating would never stop. From the multitude of practical experiments which have come under our notice, we are led to the following conclusions.

1. That the existence of a fixed mass in the shape of engine and boilers, renders the usual mode of determining the midship section of a ship inapplicable to steam-ships; and that the form must be determined with immediate reference to these. 2. That the engines of a vessel of 300 horse power occupy a space of about $\backslash frac\{1\}\{3\}$ of the beam of a ship, which necessarily is perfectly flat; and that the engine can only be firmly connected with this floor of the ship by being placed as directly in contact with it as possible; and further, that the weight of the said engine must be placed as low as possible, on account of the place of the paddle-wheel; all of which desiderata can only be obtained by making the floor of the vessel parallel to the bottom of the engine. Hence the bottom of the ship should be nearly flat across about $\backslash frac\{1\}\{3\}$ of her beam, thus:—B to B, fig. 31, nearly flat, EE the engines. 3. That no displacement is desirable on each side of the engines beyond what is required to give

an easy turn to the bilge; for it is found, as indeed it should be expected, that all displacement on each side of the engines, at the lower part of the bilge, being vacant space, or very inefficient stowage-room, is not only wasted, but tends to impair the stability and sea-worthiness of

the vessel; and, further, the engines being placed low, a species of stability of the most valuable nature is obtained. 4. That there are two ways of obtaining stability: one by having the weight of engines and boilers as low as possible, which is obtained by the means already described, and by depth in the water; the other by considerable beam. Now, beam in excess is one of the worst features of a steam-vessel. It produces a rolling oscillation, when the wind is in any degree on the beam, which impairs exceedingly the action of the paddles; it gives a species of roll, which is at the same time most distressing to passengers, and most injurious to the ship. All these bad effects are diminished, and can alone be corrected, by obtaining stability as far as possible from depth of the centre of weight rather than beam, according to the midship section already given.

The Water Lines.—Opinions on the subject of water lines, or on the degree and manner of fulness or fineness which the ends of a vessel should possess in reference to the middle, are as various as the deviations which one may conceive possible from any given shape. When with these we combine the differences of opinion concerning midship sections, which differences must also

affect very materially the form of water line, we get Steam Navigation into a labyrinth of difficulties, in the intricacies of which the good qualities of a steam-ship are so often lost.

Full round ends, convex outwardly at the bow, full above at the stern, and fine enough below to steer well, so rendering the form as like as possible to an American cotton ship, with a long straight narrow body in the middle; such a form has been introduced for steam-vessels, in the hope that the vessels, by having a small midship section and great buoyancy, might be easily propelled through the water. Even when they are made seven times as long as broad, we have seen vessels of this class turn out failures. They have, in the first place, been crank, in the second place wet, in the third place slow, and in the fourth place weak; for, by having too much bearing at the ends, and too little where the chief weight is to be supported, viz. in the middle, they have invariably bent down in the middle, and risen up at the ends.

Full round ends, combined with a full round midship section, are a modification from which much has been expected, as forming a ship of large capacity. This has been one of the worst and most extensive errors perpetrated in the construction of large steam-ships. The great breadth along the whole water line, arising from the full lines, gives an excess of superficial stability, which, with a cross sea, causes the vessel to roll violently, with an extent and abruptness of motion which the round form of the section has no tendency to prevent or retard. Then the full ends of the vessel prevent her speed through the water, and increase her motion in a heavy sea, by increasing to excess her longitudinal stability. In the next place, if the ends of the ship be used for stowage, it is plain that the great mass of matter at the two ends must render the ship labourious, or the reverse of lively, according to the nautical phrase; and the ship will less readily obey the helm. Such are some of the evils which, in many instances, and those especially in steam-ships of the largest class, have been seen to result, and which necessarily must result, from the full and round-bodied vessel used in steam navigation.

These are not all the evils of the full form. The stowage of such vessels is by no means effective in proportion to the weight, capacity, and displacement of the ship. In the first place, by giving much space on both sides of the engine-room, a very inferior species of stowage is obtained to that which results from additional length of hold. Next, the stowage-room in the end of the ship, for which so much speed is sacrificed, cannot be made effective without rendering the ship unseaworthy and unmanageable; for it is notorious, that in order to rectify the erroneous fulness for which so much is sacrificed, the ends of the ship are bulkheaded off to obtain the valuable quality of liveliness. First, then, fulness is obtained at a sacrifice of speed and seaworthiness for some supposed advantage in capacity, &c.; then, that very capacity is rendered ineffectual by the injudicious mode of its application.

An opposite school from this recommends the long straight centre body of a ship, with rectangular sections and sharp, fine, wedgelike ends. This form possesses the advantage of small transverse sections, and gives great stowage: it is an easy sea boat, and is lively from its fine ends. The principal fault in this form of vessel is its liability to crankness—its weakness at the bilge. Many of the finest steam-ships belong to this class.

The last class to which it is necessary to make a particular reference, are the steam-ships recently constructed on the wave-lines, or the hollow entrance line—on the principle which the writer of this article, by experiment and by example, has laboured to introduce. The

first vessel of this form was an experimental one of 75 feet keel, laid down in 1834. The next was a steam-vessel of 100 feet keel, constructed in 1835. The next were two pleasure yachts of Mr Ashton Smith, a wealthy proprietor in Wales, whose observation on vessels had independently led him to the conclusion that hollow lines and a peculiar midship section gave the easiest and best sea steamers; and both of these vessels, of 1838-39, though merely approximations to the true wave-lines, were remarkable for their speed and other excellent qualities. The fourth vessel of this class was the Shandon steam-vessel, altered from the old to the new lines, 1840, with a gain from the same engine of from two to three miles an hour in speed. This vessel is the property of Mr Robert Napier. The next and last vessel is the Flambeau, built in 1840, on the wave principle, by Mr Duncan of Greenock, with the co-operation of the present writer. This vessel, with the smallest proportion of power to tonnage, and with the smallest supply of steam, is, nevertheless, by far the swiftest vessel on the Clyde. The Fire-king, the largest of this new class of vessels, is 660 tons, and has engines of 220 horse power. The Flambeau has only 70 horse power to 280 tons measurement. Vessels of this class have been found at sea to be both easy, stiff, dry, and lively; while they are by far the fastest vessels of their power. The speed of the Fire-king, now the property of Mr Robert Napier, is fifteen miles an hour in still water. The speed of the smaller vessel, the Flambeau, with very deficient steam, is fourteen miles an hour; a velocity which, with her small proportion of steam-power, is only to be attributed to her superior form, and the slight degree of resistance which she encounters from the water.

The principle on which these wave-ships are constructed is, that the hollow lines forming the entrance are to correspond, as nearly as may be consistent with the form of a ship, to the form of a certain wave capable of moving with the same velocity as the vessel. The analogy between the displacement of the water by a wave of the first order, and its displacement by a vessel moving with the same velocity, being so very close as to approach to identity, rendered it probable that the same mode of displacement would be followed in both cases with the same result, viz. the production of minimum resistance. It was further to be anticipated, that as a wave, when allowed to follow the usual mode of displacing the particles of water over which it passes, presents a smooth and unbroken swelling surface, so the vessel, if of the proper shape, according to these wave-lines, would divide the water at the bow in a smooth, unbroken sheet, instead of showing the usual head of water or surge exhibited at the bow of ordinary vessels at high velocities. On the other hand, when a wave encounters a shapeless rock, or breaks on a rugged coast, it exhibits the same violent surges which are presented on the bow of vessels of the usual form. Thus, then, the analogy leads us to suppose, that the smooth, continuous, resisting displacement of a wave, would be the best method of displacement for a vessel. On submitting the question of least resistance to the elementary calculation, it appeared that the form of least resistance was very close indeed to that of the wave. The science of hydrodynamics is not, however, sufficiently matured to enable us to place implicit dependence on all the results of its calculations, unless where they are supported by actual observation; and it therefore became necessary to make the experiment.

For the purpose of determining whether this form were that of least resistance, an experimental vessel, about seventy-five feet long, was constructed on a hypothetical form of least resistance, with the wave water lines.

When this vessel was propelled at the rate of seven or eight miles an hour through the water, it was found, that instead of the usual surge exhibited at the bow of other vessels, the water was parted so smoothly and quietly, that no white spray nor other symptoms of high speed and great resistance were visible, and the parted water returned peaceably to the place it had occupied previous to the transit of the boat, with only a slight translation forwards. It appeared, therefore, from the experiment, that no greater quantity of motion was communicated to the water than was necessary to permit the vessel to pass through, and with no greater velocity than the speed of the vessel demanded. It was then presumed that this form was that of least resistance; and all subsequent experiment appears to demonstrate the truth of this inference from fact, as predicted by analogy and calculation.

It is also worthy of remark, that this form is capable of being combined with all the good qualities of a steamship, such as strength, dryness, easiness, as well as great speed; but as the construction of such vessels may still be deemed an experiment in progress, the writer will not occupy more space with observations on his own researches. Thus much he felt it his duty to communicate, in order to adapt this article to the most recent condition of steam-navigation.

The immediate Mechanism of Propulsion.—The paddle-wheel of the ordinary form (as given in the plates) seems to be the most perfect, as it is the most simple means of propelling vessels through the water. The idea soon occurred, that as the steam-engine is calculated to turn round wheels, it is only necessary to place, on a wheel on the outside of a boat, large teeth or paddle-boards to take hold of the water, and so drive the vessel forward by simply turning the wheel. It was this plan that was adopted by Jonathan Hulls, in the first plan of a steam-vessel. But there is no piece of mechanism (if we except, perhaps, the crank of the steam-engine,) which has been more despised, or which more strenuous and frequent attempts have been made to improve or supersede, than the common paddle-wheel. It is remarkable, that like the crank steam-engine, the paddle-wheel is almost universally employed in practice, after the fullest experiments of many diversified improvements. In fact, after experiments of all sorts of oars, propellers, paddles, chaplets, screws, &c., the common paddle-wheel continues to predominate as "the propeller."

The numerous faults attributed to the common paddle-wheel, are chiefly faults of misconception or malconstruction. It is easy to account for both.

When a steam-vessel is at rest in a harbour, and prevented from moving, or when in the act of setting out into motion after having been at rest, the defects of the common paddle-wheel appear to be very great. The paddle-boards, fig. 32, on entering the water, press obliquely down into it, tending to raise or lift the vessel up out of the water with a force which produces no useful effect. Again, when the paddle is rising out of the water behind, it seems to do little more than raise or drive the water upwards in the form of back water. It is only, therefore, in the middle of its path that the propulsion of the paddle seems exerted in forwarding the boat, and that only for a very short time. A large part of the force of the steam-engine seems thus to be expended in raising up the vessel, and

Na-in elevating back water, and only a small portion in carrying forward the ship. But this is the case of a vessel at rest or not in rapid motion. Now it is argued from this view of the case, that the only way in which a paddle-wheel could be made efficiently to perform its propelling duty, would be, by giving the paddle-boards such a motion upon themselves as to keep them always in a vertical position, both on entering the water and on emerging from it. This was effected about the commencement of steam navigation by Mr Buchanan of Glasgow, in what may be designated the parallel paddle-wheel.

The parallel wheel, fig. 33 is constructed on this principle, "that if two equal circles be equally divided, and so placed, that the distance between two of the points of division is equal to the distance between the centres of the circles, then will all the other points of division be also equidistant, and all the straight lines joining them be parallel." By giving to each paddle-board re-

volution on an axis, and placing an arm at right angles to it, connected by a junction-bar with an eccentric strap around the axis, the geometrical problem is mechanically constructed, and we have Buchanan's parallel paddle-wheel. This wheel, with and without alterations in mechanical structure, has been invented and reproduced over and over again. It has always failed, being radically bad.

In truth, the phenomena of a paddle-wheel revolving on a steam-boat, when the vessel is in motion, differ essentially in their form and effects from the phenomena of a wheel revolving around a centre which stands still. When the vessel is only starting, or as yet moving very slowly, all the evils here mentioned do in some degree take place; but by the motion of the vessel forwards, which is the result of the revolution of the paddles, the evils complained of are at once remedied, and the paddle of a common wheel in a quick vessel is actually "feathered," according to the most dexterous toss of the practised rower. A little study of the geometrical conditions of a paddle moving forwards and in a circle at the same time, will make this plain. Let us trace for this purpose the motion of a single paddle. At the point $o$, the paddle-board $O\text{'}$ being in the position $O\text{'}$, the

wheel, turning on a stationary axle, would bring the board $o$ successively into the positions $a,\; b,\; c,\; d,\; e,\; f,\; g,\; h,\; i,\; k,\; l,\; m,\; n$, &c.; but the axle being advanced by the motion of the boat into the places $a,\; b,\; c,\; d,\; e,\; f,\; g,\; h,\; i,\; k,\; l,\; m,\; n$,

$o,\; p,\; q$, in the same intervals of time, and these motions being simultaneous, the paddle-board describes a path in reference to the water which is the result of both, and the successive positions of the paddle-board are $aA,\; bB,\; cC,\; dD,\; eE,\; fF,\; gG$, &c. The paths described by the boards are trachoidal curves, being of the family of the cycloid. Now, from the study of the actual motion thus performed by the paddle-board of the common wheel, it is plain, first of all, that the paddle is inserted into the water in an angular position resembling closely the entrance of an oar into the water; that it is then made to act horizontally on the water during a short interval; after which it is withdrawn from the water, edgeways, in an easy and elegant manner, which the dexterous rower might envy and try to equal, but which he could hardly excel.

All this, however, takes for granted that the paddle and the boat are well proportioned and placed; otherwise all this perfection may be impaired or lost. To this exposition of the subject, it may be added, that the common paddle-wheel is in practice, as it ought to be in theory, exempt from the faults generally attributed to it; and that experiment has shown that its action presents as much perfection in operation, as its simple form and mechanical arrangements do in enabling the artist to give it durability and strength.

When the paddle-wheel is badly proportioned, badly placed, attached to a very slow or full boat, or immersed too deep in the water, its action becomes impaired or impeded. Hence much attention has been devoted to the construction of a paddle that should be more effective in these unfavourable circumstances than the common wheel; in short, to construct a paddle-wheel that should be an effective propeller, even when immersed to its axis, or wholly placed under water. This may be properly enough called the radiating paddle, as distinguished from the parallel paddle.

The radiating paddle is not constructed on the fallacious view of the subject which gave rise to the invention of the parallel paddle-wheel. On the contrary, it proceeds on the hypothesis, that the actual motion of a paddle-wheel on a moving ship is cycloidal; and its intention is to adapt the wheel with greater perfection to that cycloidal motion. The theorem on which it is founded is as follows. Let the circle in the following diagrams, figs. 35, 36, represent that circle in a paddle-wheel which is described by a point moving in the common cycloid, that is, where velocity in the circle is equal to the velocity of the vessel, $o$ being the centre of the paddle-wheel,

then, by the property of the cycloid, all lines drawn from the point $M$ at the superior extremity of the vertical diameter of that circle to $A,\; B,\; C,\; D,\; E,\; F$, &c., points in its circumference, will be parallel to the cycloid of progression, or rather to its tangents, at the points of its periphery which correspond to $A,\; B,\; C,\; D,\; E,\; F$, &c., when in motion. If it were possible to construct this

Steam Na- geometrical problem in a mechanical apparatus, this
vigation. paddle-wheel would have great efficacy even when very
deeply immersed. It is, however, difficult to make this
Propelling motion perfect at M. But this species of mechanism
Mechanism. has been very beautifully combined and arranged by
Morgan, Seaward, Cave, and others, whose geometrical
apparatus is very beautiful. Unhappily the apparatus,
even in its most perfect state, is only correct for a single
velocity of vessel and of wheel: for a different velocity,
the point of radiation of the paddles must be changed, or
loss is at once incurred. Hence it is found that this
apparatus, like the common paddle, is liable to imperfec-
tions of action, with every change of immersion and ve-
locity. When to this there are added the complexity,
friction, cost, wear and tear, liability to accident, of this
moving mechanism, introduced for obtaining the partial
remedy or slight amelioration of an evil which by proper
arrangement is but slightly felt under the old method, it
becomes manifest, that the general abandonment of the
radiating paddle-wheel, and the return to the common
one, has not been without sound practical reason.

Divided Paddle. The last species of paddle-wheel is that with the fixed
float: in other words, the simple paddle-wheel with
boards placed around its rim. Of this there are various
modifications. A very simple modification is that men-
tioned by Mr David Stevenson, in his excellent work on
the civil engineering of America. The paddle-board of
the usual wheel is, as it were, cut in two, one-half being
placed half an interval in advance of the other, as in figs.

tained without any sacrifice of power or speed. For dis-
tinction we may call this the conical paddle-wheel. It is
shown in figs. 40, 41.

Split Paddle. 37 and 38. This may be called the divided paddle-wheel.
The concussion of a paddle-wheel striking the water is
much lessened by this means, and the propelling force is
rendered more nearly uniform. Another form of this
wheel may be named the split paddle-wheel, from having
the paddle-board, as it were, split into two or more hori-
zontal slips, by which the same advantage is obtained as from
the divided paddle-wheel. It
has been proposed to place
these stripes in a cycloid; but
no advantage results from
the arrangement, although
the dignified name of the
cycloidal paddle-wheel has
been applied to it. Again,
it has been proposed to place
the paddle-boards at all sorts
of angles with the axis of the
wheel, both horizontally and
vertically, but as yet without
advantage.

A very simple expedient tends to remove all con-
siderable irregularity or concussion from the common
paddle-wheel. It is to allow the extremity of the paddle-
board nearest the side of the boat, to descend from six
to twelve inches deeper in the water than the outer ex-
tremity. This plan was carried into effect by the writer
on a steam-vessel in 1836. The desired object was at-

In the three following figures we have represented
the single oblique paddle-wheel. Fig. 44 shows the de-
velopment or stretch-out of a part of the circumfer-
ence of the wheel, to exhibit more clearly the arrange-
ment of the paddle-boards.

In figs. 45, 46, the double oblique paddle-wheel is re-
presented; and in figure 47 the development of a portion
of its circumference is given.

The Reefing Paddle.—One of the greatest improve-
ments on paddle-wheels, and one of especial impor-
tance to steam navigation, still remains to be invented

We mean such a mechanism as shall enable the steam commander to set out on a long voyage deeply laden, with a small diameter of paddle-wheel; that is, with the paddle-boards near to the axis, and to increase the (effective) diameter of the paddle, that is, to remove the paddle-boards farther from the axis, as the vessel proceeds on her voyage and is lightened by the consumption of coal. The invention of a durable, economical, and safe apparatus still remains to be made. In the infancy of steam-navigation, Mr Buchanan of Glasgow published an account and drawing of a reefing paddle;

Messrs Bolton and Watt are also in possession of a very Steam Na- old method of reefing paddles; the Society of Arts in Navigation. Scotland offered a prize several years ago for the invention, without obtaining, out of many plans, one to be recommended for practice; and, finally, the indefatigable inventor, Mr Hall of Basford, has patented a very elegant mechanism for the same purpose. It still, however, remains to introduce and establish a perfect reefing apparatus, and the author of such a system will render the common paddle-wheel a perfect propeller.

The following Table exhibits a comparative view of the Size and Power of six of the largest of the recently constructed Vessels for Transatlantic navigation.

* The three other North American Royal mail steam-ships Britannia, Caledonia, and Columbus, are of the same dimensions as the Acadia.

DESCRIPTION OF THE PLATES ON STEAM-ENGINE AND STEAM NAVIGATION.

Plate CCCCXLVIII. Figs. 1 and 2. These figures exhibit a front and side elevation of one of the simplest forms of the non-condensing steam-engine. Its principal parts are the cylinder A, the piston-rod P p, and connecting rod p K, acting directly upon the crank K X, and fly-wheel W W. Besides these there are only an eccentric and valve-rod x x x, and governor w w. Two columns and an entablature support one extremity of the crank axle, and give attachment to minor appendages. The other extremity of the axle rests on the wall of the building. To the columns is attached g g, a guide for the top of the piston-rod. The feed-pump f f f, is worked by an eccentric on the crank-shaft.

Figs. 3 and 4. The form of engine here exhibited, is of still greater mathematical simplicity than the last, although its mechanical arrangements are probably more intricate. In this engine no member intervenes between the piston-rod and the crank. A cross-head carried by the piston-rod, open in the centre, permits the crank-pin, in its circle of rotation, to oscillate freely on alternate sides of the piston; and being itself powerfully confined to motion in the vertical direction only, by the slides on the columns of the framing, the vertical motion of the piston-rod is precluded from the production of any other dynamical effect than the most direct of all possible conversions of rectilinear into rotatory motion. The cross-head is marked H H in the figure, the columns being marked m m. The other letters refer to the same parts as in the last figure.

Figs. 5 and 6. In these figures the high-pressure engine is represented in its most improved form for stationary purposes. It is analogous, in the arrangement of its principal parts, to the usual construction of Bolton and Watt's condensing-engine. A cast-iron base supporting six columns and an entablature, forms a framing upon which the parts of the engine are distributed, so as to form what is called a Portable Engine, being entirely independent of the building in which it may happen to be placed. At one extremity of the base is placed the cylinder A A, and at the other the crank-

axle X, and fly-wheel W W. The motion is transferred from the piston P p, through the great lever L L L, and connecting rod or crank-rod L K. The feed-pump f f is in this instance worked from the point m of the parallel motion, in the way generally adopted in condensing engines for working the air-pump, whose place in fact it here occupies. The valve is a short D-slide, worked by eccentric gear, x x x x. S is the steam-pipe. The education pipes E are seen descending on both sides of the valve-casing; they unite in a common chamber beneath the cylinder, whence a pipe conveys the educted steam to the chimney, or to serve some other purpose, as the case may be. The governor acts as in the previous case. This drawing is taken from the form of engine manufactured by Messrs Caird and Company.

Figs. 7 and 8 is a form of the upright condensing engine manufactured by Messrs Carmichael of Dundee, and successfully applied by them to various purposes. It is compact and has been found to work well.

The cylinder A A is placed upon the floor, and on either side of it stands a cast-iron column. These columns are hollow and are used as steam-pipes, S S S S, to convey the steam to the jacket of the cylinder, from which it finds its way into the valve-chest D. On the top of the columns is a cross-beam sustaining the crank axle, and the columns support guides m m m m, on which, by means of wheels g g, and a cross-head g p g, the piston-rod P p is maintained in its vertical position, so that the connecting rod p K is directly attached to the crank-pin K. The air-pump G is worked from the crank-shaft by means of a second crank or bend, and an eccentric x x works directly the slide valve; f f is the feed-pump for the boiler, worked directly from the air-pump cross-head; w w w w is the governor, with its appendages; G is the condenser; N the cold well.

Plate CCCCXLIX. In fig. 1. of this plate we have given a sectional elevation of a land-engine of twenty-five inch cylinder and five feet stroke. In fig. 2. we have given its horizontal section at the level of the base of the cylinder, and in the remaining figures the details of its

Steam Na-vigation. different parts. In figs. 1 and 2 AA is the cylinder, P the piston, Pp the piston rod, Bb the parallel motion, LLL the great lever. The pillow blocks L, in which the centre of the great lever works, rest on the spring beam UU, whose ends are secured to the walls of the building in the manner shown on the next plate. The centre of the spring beam is sustained by the columns VV and their entablature u, which crosses the building and has its ends secured to the walls like those of the spring beams. At the other end of the great lever are the connecting rod LK, the crank KX, and fly-wheel WW. Returning to the cylinder we have, DD the slide-valves and their casing; dd the packing ports. The valve-casing terminates below in EE the eduction-pipe leading into the condenser C. G is the air-pump, F the place of the foot-valve, h the air-pump piston-rod. The condenser and air-pump with their appendages are placed in the cold well N. M is the hot well into which the contents of the air-pump are discharged, and from which the hot water pump m draws its supply by the pipe m'. The pipe oo leads from the hot water pump for the supply of the boiler. The cold well is supplied from the cold water pump n by the pipe n n'. The rods for working the hot and cold water pumps hang from a stud at either side of the lever at m. The governor ww is supported on a bracket u, which bridges across the main shaft. The influence of the governor is conveyed to the throttle-valve by the levers and connecting rods wwww. The valves are worked by the eccentric xxx. ff is the eccentric shaft which carries the gab-lever f' on which the eccentric rod acts; it also carries the levers for working the side rods of the valves, the levers which carry the counterbalance weight, and the socket for the starting lever. The small pillars TT, which surround the cylinder, are surmounted by an entablature which serves as a support for a gangway round the cylinder.

The remaining figures on the plate represent in detail the different parts of the engine which we have just described, separated from each other, in order more clearly to exhibit their construction. Figs. A A' a a' show the details of the cylinder. In A A' is shown the upper and lower ports of the cylinder at 1 and 2, and the steam port at 3. In A', 4 is the cylinder cover, and 5 the stuffing box. a is a horizontal section of the cylinder, and a' a plan of the cylinder cover.

Figs. DD' dd' show the slide-valve casing; D a front view, D' a side view. 1 and 1 are the packing ports, 2 and 2 the packing-port covers, 3 the eduction-pipe, d the cover of the slide-valve casing, 4 its stuffing-box, d' a section of the casing. Figs. C, G, F, show a side elevation of the condenser, foot-valve, and air-pump; C, G, F, a section of these; and c, g, f, a plan of them. 1 is the cover of the foot-valve, 2 and 3 a section and front view of the valve. Fig. L shows a side view of the great lever, L 1 a top view, and L 2 a transverse section through the centre of it. Figs. KK' show a front view and section of the crank. Figs. XX' show a side view, an end view, and a plan, of the crank shaft pillow block. Figs. l, l1, l2, show a side view, an end view, and a plan of the pillow block for the main centre of the great lever. Figs. mm' show a vertical and horizontal section of the hot water pump, and figs. nn' of the cold water pump. Figs. B 1, 2, 3 are the details of the main links of the parallel motion; b 4, 5, 6, 7, 8 details of its air-pump links; 9, 10, 11, 12 side and top views of its radius and parallel bars. 13, 14 is the clutch for the top of piston-rod; 15, 16, gudgeon and clutch for the top of air-pump rod; 17, 18, top and side views of the ring gudgeon to which the parallel rods are attached; P piston-rod, H air-pump piston-rod, h air-pump rod, gg cold water pump-rod and piston-rod, and g' g' hot water pump-rod and piston-rod;

x the eccentric, WW, 1, 2, 3, 4 details of the fly wheel, Steam. O main centre or gudgeon for the great lever. PP 1 vign. plan and section of the piston, w w' 1, 2, 3, 4, 5 details of the governor, w the spindle, w' the slide, 1 1 the radius arms to which the balls 5 5 are attached, 2 2 the radius arms which cause the balls to act on the sliding collar w', 3 and 4 the stay for confining the motion of the balls. t 1 2 is the slide-valve rod and side rods, t 3 is the slide-valve cross-head, R R' a side and front view of the connecting rod.

Plate CCCCLXX exhibits a Sectional Elevation of a Condensing Engine. This description of house engine is the design of Mr McNaught of Glasgow, and has been extensively applied by him to cotton, silk, and saw-mills. The principal peculiarity in its structure is the arrangement by which no further masonry is required for its foundation than the building in which it stands, the usual cold well being dispensed with, and the whole structure connected by cast-iron beams with the walls of the house. The cylinder AA is attached immediately to TT, the cast-iron beams of the floor, which are deeply bedded in the wall at T and T, and rests directly upon the large vessel C, which forms the condenser, and is supported likewise by beams YY, which are bedded in the walls. The condensation is effected by injection alone, without the usual accompaniment of a cold well around the condenser, an appendage that may safely be regarded as by no means indispensable to the practical perfection of the vacuum—when the vessel itself is formed with few joints. The transverse beams of the buildings are supported by two pillars directly under the centre of the great lever LLL, so as to support the main centre L; and the crank-axle X and the axis Z of the fly-wheel W, are supported on UU, another beam of cast iron.

The steam enters the house through the pipe SS, passes round the cylinder to SS, around the long slide-valve DD, being confined to the middle of it by the valve packing hh, and after performing its duty in the cylinder, passes out at EEE into the condenser C, where it is finally condensed into water. Hence it is drawn off at the foot-valve F by the piston H of the air-pump G, and delivered by the discharge-valve M into N, the hot well. The slide-valve DD is worked by the eccentric gear xxx and the rod dd through a moveable stuffing-box dx.

Plates CCCCLXXI, CCCCLXXII. These plates represent the high-pressure engines which are employed to work the inclined plane at the Liverpool station on the Liverpool and Manchester Railway. They are beautiful and in many respects highly judicious; they are the work of Messrs Mather, Dixon & Co., Liverpool.

WWW, Plate CCCCLXXII, is the great wheel which works the rope that draws the railway train up the inclined plane; the rope is contained in a groove in the edge of the wheel. A clutch kk connects or disconnects the crank-axle XXX with the wheel WW; the cranks KX, KX, KX are placed at right angles, so that when one is on the centre the other is at the furthest distance from it. Kk, the connecting rod, hangs down from LL, the ends of the levers. The centre of the side levers, IV., rests on a truss at no greater height than three feet above the floor of the engine-room. Lp is a side rod by which the levers are united to the cross-head rpr. The steam in this instance comes about a quarter of a mile from the boilers to the cylinders AA by the steam-pipe SSS. Fig. 2 is a section of the steam-valves and cylinder. The valves DD are short D-slides, surrounded by steam, and by the underside of the valves the escape takes place through the space E; dd is the valve-rod moved by the usual valve-gear xxx. The eccentric xxx, Plate CCCCLXXI, is placed on a long shaft from the

Na. crank-axle at X, which shaft is also employed to work the governor-balls ww. The whole foundations are solid red sandstone rock, in which excavations are made for the shafts and ropes.

Plates cccclxxiii, cccclxxiv, cccclxxv. This very beautiful pair of engines was constructed by Mr Fairbairn of Manchester; and they are the property of Messrs Bailey and Co. of Staley Bridge, near Manchester. They are employed to drive a cotton-mill, and possess many excellent adaptations to this purpose.

These engines are of a similar form to those employed in large steam-vessels, and will serve very well to conduct the student from the common to the marine engine. The working beam or great lever LLL is, as it were, split in two, one of the halves being placed on each side of the engine, but united at the middle by a large gudgeon or main-centre, LL, and at the one end by a cross-head, LpL, and side rods, RL and RL, and at the other end by a cross-tail of similar form, and the connecting rod KL, which turns the crank KX. The moving mass is thus placed lower, and the whole rendered more compact, than the common horse-engine.

This double marine engine is reckoned preferable in the manufacture of cotton to an engine of the common kind. The double engine gives a considerable degree of uniformity to the velocity produced; and the approximation to uniformity is rendered still more perfect by the short stroke, in which the variations of force recur at shorter intervals than with a long stroke. A striking peculiarity in this pair of engines is the large fly-wheel, WWW, formed of toothed segments, which receives the moving force of both engines, and gives it out directly, and with a high velocity, to the mill-shafts, YY. Not only is the requisite speed of revolution attained very readily and quickly by this means, but the momentum of the wheel is immediately conveyed to the shaft, instead of passing through a series of wheel and axle work. The durability and excellence of this arrangement are unquestionable.

The section, fig. 1, plate cccclxxiv, shows the details of many of the parts. The steam-pipe SSS from the boiler conducts the steam into a space SS, forming a jacket round the cylinder AA. The piston P has metallic rings on its periphery as packing; U and V, the upper and lower steam-ports, are wholly formed in the cover and bottom plate of the cylinder, and are closed and opened alternately by two short D-slides in two separate valve-chests above and below. The steam enters the upper chest from the jacket at S, where the throttle valve is inserted, and passes through the valve. The packing on the back of the valve is screwed down from above by a vertical spindle, and the eduction takes place through E by a hollow vertical column on one side of the valve-chest, while the steam passes down to the lower port through another column. The condenser C is a single casting, placed immediately below the valve-chest, and is entered by the injection pipe cc at c, of which the aperture is regulated by a slide-valve and vertical spindle ending in a screw. F is the foot-valve, governing the communication between the condenser and air-pump G; H is the air-pump piston, with common clack-valves; and M is the delivery-valve, opening outwards into the hot well. The waste-pipe is immediately below M; and the feed-pump and pipe f are in the masonry below the lever, so as to draw the feed-water from the waste-pipe.

The valves DD receive motion by an apparatus somewhat peculiar. A stud in the crank-pin K carries round a small radius rod xx on an axis, concentric with the crank; a smaller crank on this axis or shaft has a length equal to half the throw of the valve, or equal to that which would be given to the usual eccentric, and by a bar xx similar to the eccentric rod, the valve is moved by

this lesser crank, just as by an eccentric. This gearing has the advantage of lightness and precision. m m m are the usual links of the parallel motion; d is a counterpoise to the weight of the valve, w w are the weights of the governor.

Plate cccclxxvi. This is one of that class called the rotatory steam-engine; a class comprehending many varieties, of which we hear much and see but little. The engine is here given as an illustration of this very unsuccessful class of engines, by one of its least exceptionable examples. It has actually been in use for some years, being frequently employed to turn the machinery of a large establishment. We have seen it working smoothly and well. Yet we have not been able to recognize in it any reason for giving it an equality, much less a preference, in comparison with the common engine. It can be reversed in the same way as a common engine. It was invented by Mr Yule of Glasgow, by whom it was patented, and is still in the works of Thomas Edington, Esq., at Glasgow.

SSS is a double steam-pipe, either branch of which may be employed according as the engine is to go forward or backward. AA is the cylinder firmly fixed on a stone foundation, and in its centre is an axis XX, upon one side of which and eccentric to the cylinder is an inner cylinder or barrel turned quite true, and fixed to revolve with the axis X, and so to form the piston P, which is to receive and give out the force of the steam. RR furnishes the point d'appui, the surface of reaction, which resists the force of the steam and forms a fixed obstacle. It is a flat slide or sluice, (see fig. 5,) resting on the barrel piston P, and maintained by guides always in a vertical position. It passes into the cylinder through a rectangular stuffing box, and is raised and depressed by a small eccentric pin xx, so as to remain always upon the surface of the piston drum. All the working surfaces are rendered steam-tight by metallic packings. EEE is the eduction passage into the condenser or the open air, DD are slide-valves to be reversed when the engine is to go backwards. On the revolving axis of the piston X are toothed wheels, gg, working other two, gg, which have a common axis zz, carrying a fly-wheel, and driving the machinery to be worked by the engine. Fig. 6, shows the ports at DD. Fig. 7 shows the guides of the slide RR.

Plates cccclxxvii, cccclxxviii, cccclxxix exhibit views of a pair of beautiful marine engines, constructed by Mr Napier, for the four British and North American royal mail steam-ships Britannia, Acadia, Caledonia, and Columbia, plying between Liverpool, Halifax, (Nova Scotia) and Boston, (U. S.) The following are the general dimensions of the vessel and engines.

The power of the engines is about 240 horse power. The paddle shafts make 16 revolutions per minute. The tonnage of the vessel by the old law is about 1200 tons.

Plate cccclxxvii is a side elevation of one of the engines.

Plate cccclxxviii is the elevation of the crank end of the engines, and Plate cccclxxix the elevation of the cylinder end. By an inspection of these engravings it will be seen, that the parts of the engines are sus-

Steam Navigation. Stained by an elegant and rigid Gothic framing, rendering them, notwithstanding the ponderosity of their different parts, entirely independent of the vessel on which they are placed. AA are the cylinders, B the slide-valve casing, C the condenser, D the hot well and air-vessel placed on the top of the condenser, E the air-pump, FF the feed-pumps. The moving parts of the engine are as follow:—K the cylinder piston-rod, I the cross-head, H the cylinder side rods descending to the great side levers GGG. Connected with the parts last described are the radius rods of the parallel motion L, the motion side rod L', and the parallel motion shaft l, V the valve or weigh-shaft on which is fixed the valve lever W, whose other end is inserted into a clutch on the slide-valve link c. On either side of the centre of the great lever depends a side rod ff, to work the bilge and brine pumps, and to its extremity are attached the links of the cross-tail of the connecting rods, P the links, Q the cross-tail, R the connecting rod. To the upper end of the connecting rod is attached the crank S; T is the intermediate or crank-shaft, TT' the paddle-wheel shafts. On the crank-shaft is placed the eccentric U; and uu is the eccentric rod working the eccentric gab-lever v on the valve or weigh-shaft t t'. Y yy the expansion valve apparatus, h h escape valves at top and bottom of cylinders, X paddle wheels, k lever for starting the engines, 1 1 steam-pipes, 2 2 waste water pipes from hot well, 3 double force-pump for filling boilers, extinguishing fires, and washing decks, 4 4 engine beams, 5 5 5 5 midship section of vessel, 6 6 thick planks checked in upon and bolted through the timbers thus:—

Plate cccclxxx. Side and end elevation of one of the engines of her Majesty's mail packet, Urgent, and also of the Actæon, built by Messrs Caird and Company of Greenock. The Urgent plies between Liverpool and Dublin; the Actæon between Liverpool and Glasgow. Both vessels have been very successful: they are swift boats, and consume a small amount of fuel. Their general dimensions are here noted.

The power of each of the engines is 140 horse power. The paddle-shaft makes about twenty revolutions per minute. The tonnage of the Urgent, by the old law, is 5625$\backslash frac\{1\}\{2\}$—of the Actæon 551$\backslash frac\{1\}\{2\}$. AA is the cylinder, C the condenser, E the air-pump, H the cylinder side rods, I the cylinder cross-head, B the valve-casing, W the valve lever, W' the back balance, GGG the side levers, P the cross-tail links, Q the cross-tail, R the connecting rod, S the crank, U the eccentric, N the air-pump side rods, M the air-pump cross-head.

Plates cccclxxx, cccclxxxii, cccclxxxiii, represent the engines of the Achilles, also built by Messrs Caird and Company, to ply between Liverpool and Glasgow. Plates cccclxxx, cccclxxxii, show the two side elevations of one of the engines; and plate cccclxxxiii a

section of the vessel to a lesser scale, with the engines, Stair paddle-wheels, &c., in situ. The arrangement of the framing of these engines is highly beautiful. The entablature supported by the columns, uniting both engines in one design, gives massiness of appearance, as well as great strength to the structure. In plate cccclxxxii is seen the apparatus for working the engines expansively. On the crank-axle T is placed a series of cams, t t t, which act upon the roller of the expansion-valve tumbler. Y y y are the expansion-valve connecting rods and levers. Z is the valve-chest, and the valve is of the kind called equilibrium valves, or crown valves. The other parts are A the cylinder, B the valve-chest, C the condenser, D the hot well, E the air-pump, F the feed and bilge pumps, GG the great lever, G its main gudgeon, H the cylinder side rods, I the cross-head, K the piston-rod, L L the parallel motion, M the air-pump cross-head, N the air-pump side rods, O the air-pump piston-rod, P the connecting rod cross-tail links, Q the cross-tail, R the connecting rod, S the crank, U the eccentric pulley or cam, u u u the eccentric rod, V the valve-shaft, W W the valve-lever and counter balance lever.

Plates cccclxxxiv, cccclxxxv, cccclxxxvi. The engines exhibited in these plates are a pair of 110 horse power each, constructed by Messrs Fawcett, Preston & Co. of Liverpool.

Plate cccclxxxiv shows the side elevation of one of these engines. Plate cccclxxxv shows the elevation of the crank end of both engines; and plate cccclxxxvi the cylinder end of the engines, drawn to a somewhat smaller scale. The letters refer to the same parts as in the engines already described, and it is unnecessary here to repeat the description.

Plate cccclxxxvii. In this plate is given a representation of a single marine engine of 65 horse power, with a stroke of four feet. Fig. 1 is a side elevation; fig. 2 a plan or bird's-eye view; fig. 3 an elevation of the cylinder end; and fig. 4 an elevation of the crank end. The same letters indicate the same parts as in the former figures.

Plate cccclxxxviii, fig. 1. is an end view, and fig. 2 a side view, of a double towing-engine of forty-five horse power and three feet six inches' stroke. The most striking peculiarity of this engine is, that the paddle-wheel shaft is separate from the crank-shaft, and driven by it through the intervention of toothed wheels. T is the cranks haft, with its spur wheel driving the spur wheel of the paddle-shaft T'. The other letters refer to the same parts as before.

Plate cccclxxxix. In this plate are represented two engines of direct connexion, constructed by Messrs Tod and McGregor, Glasgow.

In figs. 1 and 2 of this plate, the crank S of the engine is placed directly above the cylinder A; the piston-rod K carries a cross-head I, which is guided to move in the vertical direction by two cross guides gg, one at each extremity, whose ends slide upon the vertical pillars pp, which sustain the framing for the support of the crank-axle. From each end of the piston cross-head depends a side rod HH, whose lower extremity, together with the ends of the side rods PP, which depend from the cross-tail Q of the connecting rod R, are attached to the end of a side lever GG. To the opposite end of the side levers are attached the side rods N of the air-pump, and on either side of its centre the side rods of the feed and bilge pumps F. The parts not already described are aa the slide-valve, C the condenser, E the air-pump, S the crank, U the eccentric, and uu the eccentric rod and valve-gear.

In the engine represented in figs. 3 and 4, the pis-

Na. ton-rod K terminates in a triangular frame III, from the apex of which the connecting rod R descends to the crank S; and to the extremities of its base are attached the piston-rods OO of the air-pumps EE, which are in this case two in number, and situated one on each side of the cylinder. The triangular frame III is confined to move in a vertical direction, by its cross-head gg being guided in the slide pp. The remaining parts are, A the cylinder, CC the condensers, aa the valve-chest, F the feed-pumps, worked by an eccentric ff, Uu the eccentric and valve-gear, and eee e the framing of the engine.

Plate ccccxc. Fig. 1 of this plate is a side-elevation, and fig. 2 an elevation of the cylinder end, of a pair

of marine engines constructed by Messrs Seaward of the Steam Navigation. Canal Ironworks, Limehouse, for H. M. steam-frigates Gorgon, Cyclops, Prometheus, and Elector. These engines are of a peculiar construction; the crank, as in the engines of the last plate, being directly above the cylinder, the connecting rod only intervening between it and the piston-rod. They are of the class of the vibrating pillar-engines, the pillar which supports the beam turning upon a centre at its lower end. A is the cylinder, B the valve-chest, C the condenser, E the air-pump, K the piston-rod, R the connecting rod, S the crank, GGG the beam, g the vibrating pillar, L the radius-rod, N the air-pump side rod, M the air-pump cross-head.

STEEL.—As good iron is the basis of good steel, all that has been said under the articles IRON and SMELTING in reference to the sources and means of procuring that metal in a state of purity, may be advantageously referred to as a preliminary to the present.

Steel is a carburet of iron, with probably a slight mixture of other substances which are more or less essential to its perfection, and certainly in most cases with some alloy which is not essential, but which, on the contrary, is to some extent injurious. This description would equally apply to cast-iron, which differs from steel as to its ingredients principally in the quantity of carbon, cast-iron having sometimes one-fifteenth part, and good steel seldom more than one two-hundredth part of that substance. The difference between the proportions of the carbon does little, however, to explain the difference between cast-iron and steel; for, while the condition of cast-iron is retained, it is found that diminishing the quantity of carbon renders it still less like good steel. It appears, in short, that the good qualities of steel—and they are very various—depend upon circumstances partly chemical and partly mechanical, which have hitherto defied analysis. It is not even precisely known whether the union of the iron and carbon is a chemical or mechanical union: perhaps it may be partly one and partly the other, for reasons which will presently be given.

In consequence of this ignorance as to what constitutes the essential qualities of good steel, the processes by which favourable results have been obtained have in nearly all cases been empirical, and in many instances have been real or pretended secrets. The processes are of a nature to forbid any very nice calculations, and they are liable to great and unappreciable modifications in the execution. For example, steel being, as before stated, a carburet of iron, and having generally a slight admixture of oxide of iron, must be subject to many incalculable changes during its successive exposures to violent heat in contact with carbonaceous fuel and atmospheric air. Moreover, the hammering, on which many of its good properties depend, is obviously an operation which cannot be meted out with very scrupulous nicety, and is besides liable to be very much influenced by the temperature of the metal and by the direction of the blows in reference to the mechanical structure of the mass.

A good practical essay on steel, it is therefore evident, would consist in an exceedingly minute detail of the actual operations applied to a certain description of ore, or to a known specimen of manufactured iron, which, with certain sorts of fuel, had been found uniformly to produce steel peculiarly adapted to certain purposes. Such an essay would form a volume, and it would still

convey imperfectly what it professed to teach, because in all the processes there are certain stages of the conversion whose advent is judged of by the experienced eye and hand of the skilful workman, from symptoms which can be explained only to the sight and touch. Here we only propose to describe, in very general terms, some of the principal processes, so as to convey a knowledge of the theory of steel-making without professing to give the actual practice. We must pre-mise, that the destination of the steel is of great importance in estimating even the theory of those processes, as may be well supposed when it is recollected that a lancet will fracture almost like glass, while a bricklayer's trowel is required to cut the most refractory lump of semi-vitrified clay in the shape of a brick. These two instruments are perhaps at the extremities of the scale, the perfect hardness and brittleness of the lancet contrasting with the extraordinary toughness and tenacity of the trowel.

It was at one time, indeed, thought so difficult to combine these last-mentioned qualities with sufficient hardness to sever a good stock-brick, that trowels were made of a plate of iron to supply the toughness, and an edge of steel to give the hardness. Even at the present time it is supposed that the peculiar qualities of certain sword-blades result from their being combinations of hard steel with soft tenacious iron fibre; and that the variegated or damasked surface of such blades is owing to the different appearances presented by the iron and steel. By some this effect has been supposed to result from chemical changes acting partially upon the original carburet, depositing the carbon more profusely in some parts of the iron than in others. It may arise, as already hinted, from some portions of the carburet being in a chemical, and others only in a mechanical state of union. According to other authorities, the structure in question has been manufactured expressly by binding up portions of soft iron wire with ingots of steel, and hammering the whole into a mass at a high temperature. Such a process will, it is known, produce very similar appearances. Whatever be the truth in regard to the sword-blades, certain combinations of iron and steel in parallel laminae are advantageously employed for some purposes. The carpenter's plane-iron, for example, consists of a very thin hard steel face on an iron back; because this instrument requires to unite a cutting edge nearly equal to that of the lancet with a tenacity which shall encounter uninjured the hardest knots; a trial almost as severe as that applied to the trowel.

One great cause of the uncertainty and obscurity attending the practice of steel-making, is the importance of the hammering or other mechanical parts of the operation. If

the distinction between good and bad steel were principally chemical, the production of the former would long since have been rendered easy and determinate. How little this is the case may be inferred from the fact, that the elaborate series of experiments conducted a few years since by Dr Faraday and Mr Stodart have scarcely added a new fact to the science of steel-making; while, on the other hand, the immense value of mechanical action is shown, among numerous instances, by the increased strength of dracon iron wire as compared with rolled iron of equal size, a difference amounting sometimes to sixty or seventy per cent.

The remarkable qualities of the trowels for which a Mr. Walby was celebrated about forty years since, resulted in a great measure, if not entirely, from good and rapid hammering at a moderate temperature. The object of hammering being to condense the steel, it is evident that when at a white heat, in a state approaching to fusion, the mass is so plastic, it yields so freely, that hammering is perfectly inoperative, except to change the external form; while, on the other hand, if the mass be cold, it is so unsusceptible of what may be called intestinal movement among its particles that the most violent hammering can do little more than dislocate portions of the surface, which will accordingly crack or scale off. Between these extremes a medium may be found, and was, we believe, found by Mr Walby. His hammering was principally performed at a low cherry-red heat; and, by means of a peculiar and ingeniously mounted hammer of considerable weight, he was enabled to do all that was required before the temperature was sensibly lowered. But, as we are informed, he did more than this. It is quite certain that in hammering any mass, and especially in a thin plate, the central cannot be under the same circumstances as the exterior portions. Not only will the centre retain its heat somewhat longer, but, what is of more consequence, the tendency of the central portions to spread laterally under the hammer, is resisted by the marginal parts; while these latter not being so protected by a belt, spread freely, and perhaps separate into detached pieces. If, for example, a circular disc of steel at a low temperature were violently beaten under a flat hammer, it would be very much condensed in the middle, while the circumference would gradually separate, showing radial splits or cracks. The most perfect way to condense a circular disc of metal would obviously be to confine it in a very strongly defended cavity, whose walls should prevent all lateral spreading, and thus the full effect of each blow would be felt in condensation. Such a process is, however, inapplicable to trowel making, and perhaps to all other purposes except the striking of medals, where we see it employed; but Mr Walby obtained nearly all the effect of such an arrangement by forging each trowel considerably larger than it was ultimately intended to be, and cutting off about an inch of superfluous metal after the hammering was completed; cutting off, that is to say, the wall which had acted to restrain the spreading of the central portion of the blade, and which had probably become loose and spongy itself for want of such restraint, thus leaving only the close compact metal in the finished trowel.

Having thus endeavoured to direct the reader's attention to some of the qualities demanded in steel, and to the causes which affect their production, we shall briefly describe some of the operations.

Steel is most frequently made from rolled bars of good, by which we mean pure iron. To communicate to these bars the desired quantity of carbon, they are formed into bundles, and are placed in a large stove or furnace alternating with layers of carbon, (hard-wood charcoal is preferred,) and a high temperature being maintained

for a week or ten days, the iron gradually absorbs the required quantity of carbon, and becomes converted into steel. The completeness of this conversion is judged of from time to time by the examination of certain of the bars, which are so disposed as to be accessible for this purpose. If the carbon has not penetrated to the centre of the metal, this will be evident on breaking the bar transversely, as the section will exhibit a colour in the centre different from that near the surface: it will show what the workmen call a pith. Towards the end of the process, the watching requires to be skilful and constant, because, if the absorption of carbon becomes very excessive, the metal may be rendered so fusible as suddenly to melt; and though this would be of little consequence in a sound crucible, it would be attended with great loss in a large stove or hearth. The surface of the bars becomes so nearly in this condition that it is always blistered by the escape or rarefaction of air or gas from the interior of the metal; and hence bars so prepared have acquired the name of blister or blistered steel. The process itself is called cementation.

The bars thus prepared do not differ very greatly from cast-iron, except in the smaller quantity of carbon which they contain, and in their freedom from impurities. They have somewhat more malleability and tenacity than cast-iron, but not so much as is imparted to that substance during its conversion to bar-iron, and which must now, except for very coarse purposes, be communicated to these bars of cementation—without, however, depriving them of their carbon. With this view the bars so prepared are broken up into short lengths, are made into bundles, heated almost to a white heat, hammered, welded together, re-broken and re-hammered till they are reduced as nearly as possible to a compact homogeneous mass of greater specific gravity than in their former state. In all these weldings, care is required to preserve the surfaces clean and unoxidized, as upon this depends the perfect union of the two surfaces.

This care is dispensed with in the processes for making cast-steel, the nature of which has been already indicated in describing that of cementation. The pure iron and a certain proportion of carbon are fused together in a crucible, and being cast into ingots, these are treated somewhat like the bundles of the cemented bars. They are hammered at a high temperature till they are rendered malleable and dense, and till a certain portion of the carbon is displaced, that substance being generally in excess. Various modes of applying the carbon have been proposed; but it is very difficult to determine in the abstract which of these is the best. One mode of application is, by the introduction of a stream of gas. Cast-steel is free from the defects which are liable to attend the imperfect welding of the bars, and is likely to supersede all others for the finer purposes of cutlery. It requires, however, the most skilful manipulation as the point of sufficient fusion is reached, and this must be performed under the most severe exposure to heat; so severe as to demand that the workmen should be protected, by clothing of wetted sackcloth, from the joint effects of the opened furnace and the glowing crucible. This combination of skill and severe labour secures high wages, and enhances the price of the article.

The experiments of Faraday and Stodart, before alluded to, were undertaken not so much to improve the mode of manufacture as to determine the effect of various alloys; it having been inferred, partly from the condensation which frequently accompanies chemical unions, and partly from the examination of certain specimens of steel which were known to possess good qualities, that a small portion of foreign matter might be beneficially introduced. With this view, alloys