informed that it is capable of raising a number of pounds through a certain space in a certain time. Messrs. Watt and Boulton suppose a horse capable of raising 32,000 pounds avoirdupois, 1 foot high in a minute, while Dr. Desaguliers makes it 27,500 pounds, and Mr. Smeaton only 22,916. If we divide, therefore, the number of pounds which any steam-engine can raise 1 foot high in a minute, by these three numbers, each quotient will represent the number of horses to which the engine is equivalent. Thus, in the present example = 37, horses, according to Watt and Boulton; 243 horses, according to Desaguliers; and 1194336 32000 22918 =52 horses, according to Smeaton. In this calculation it is supposed that the engine works only eight hours a day; so that if it wrought during the whole 24 hours, it would be equivalent to thrice the number of horses found by the preceding rule. Before concluding this article, we shall state the performance of some of these engines, as determined by experiment. An engine whose cylinder is 31 inches in diameter, and which makes 17 double strokes per minute, is equivalent to 40 horses, working day and night, and burns 11,000 pounds of Staffordshire coal per day. When the cylinder is 19 inches and the engine makes 25 strokes of 4 feet each per minute, its power is equal to that of 12 horses working constantly, and burns 3,700 pounds of coals per day. And a cylinder of 24 inches which makes 22 strokes of 5 feet each, performs the work of 20 horses, working constantly, and burns 5,500 pounds of coals. Mr. Boulton has estimated their performance in a different manner. He states that I bushel of Newcastle coals, containing 84 pounds, will raise 30 million pounds 1 foot high; that it will grind and dress 11 bushels of wheat; that it will slit and draw into nails 5 cwt. of iron; that it will drive 1000 cotton spindles, with all the preparation machinery, with the proper velocity; and that these effects are equivalent to the work of 10 horses. (Brewster's Ferguson.) The largest steam-engine which we believe has been ever erected was set up in 1811, by Mr. Mayle, at Chauwater mine in Cornwall. It is equal in power to 1010 horses; and is employed in keeping dry by pumps a mine of 100 fathoms deep. It is much to be regretted that in the country where all the great and essential improvements in steam-engines have been made, and where so noble a species of mechanism was invented, there is no separate treatise on their construction and history. What is here given is a mere collection, correct, it is hoped, bu very limited. They who wish to go farther into this interesting enquiry may turn to the article STEAM-engine in the Encyclo pædia Britannica, the Pantologia, and Brewster's Ferguson's Lectures; to the successive volumes of the Repertory of Arts and Manufactures, to the 2d volume of Prony, Architecture Hydraulique, and to Hachette, Traité des Machines. Mr. Robertson Buchanan's treatises on the "Economy of Fuel, and on Locomotive Machinery," will, we doubt not, go far towards supplying an important desideratum: but something else will still be wanting, we apprehend, in reference to this point. STEAM-boats. Several attempts have been made to apply the force of steam to the purpose of propelling boats. One of the earliest projects of this kind was in 1736, when a patent was taken out for a boat to be moved by steam. The next was that of Mr. Symington. In his boat, by placing the cylinder nearly in a horizontal position, the introduction of a beam is avoided. The piston is supported in its position by friction wheels, and communicates, by means of a joint,with a crank, connected with a wheel, which gives the water-wheel, by means of its teeth, a motion somewhat slower than its own; the water-wheel serving also as a fly. This water-wheel is situated in a cavity near the stern, and in the middle of the breadth of the boat, so that it becomes necessary to have two rudders, one on each side, connected together by rods, which are moved by a winch near the head of the boat, so that the person who attends the engine may also steer. Mr. Symington has likewise placed an arrangement of stampers at the head of the boat, for the purpose of breaking the ice on canals, an operation often attended with great labour and expense. These stampers are raised in succession by levers, the ends of which are depressed by the pins of wheels turned by an axis communicating with the water-wheel. A dreawing of this steam-boat is given by Dr. Young in the 1st vol. of his Natural Philosophy. Steam-boats now work on the passage between London and Gravesend; and several are employed on different canals in Scotland. The following account of the steam-boats on the Clyde, by Mr. Robertson Buchanan, of Glasgow, was published in No. 203 of Tilloch's Philosophical Magazine. "So early as the year 1801, a vessel propelled by steam was tried on the Forth and Clyde inland navigation, but was laid aside, among other reasons, on account of the injury it threatened the banks of the canal by the agitation of the water: and as far as I can learn, the same objection still subsists to the use of steam-boats on artificial canals so narrow as those usual in Great Britain. That objection, however, I should think, does not apply to some of those of Holland and other countries on the continent. "The first attempt on any scale worthy of notice, to navigate by steam on the river Clyde, was in the year 1812*. A passage boat of about 40 feet keel and 10 feet beam, having a steamengine of only three horses' power, began to ply on the river. Since that period the number of boats has gradually increased. "Besides three vessels which have left the Clyde, there are six at present plying on the river, two of which carry goods as well as passengers. They have on the whole been gradually increased in tonnage as well as in the power of their engines; and still larger boats and more powerful engines are now con structing: among others one of about 100 feet keel and 17 feet beam with an engine of 24 horses' power; and one of equal burthen, having an engine of 30 horses' power. These boats are all neatly fitted up, and some of them even elegantly decorated. "On board all the passage steam-boats are newspapers, pamphlets, books, &c. for the amusement of the passengers, and such refreshments as are desirable on so short a voyage, a distance of about 26 miles by water, and 24 by land. "The voyage betwixt Glasgow and Greenock, including stoppages at intermediate places, is commonly accomplished in from three to four hours, the vessels taking advantage of the tide as far as circumstances will permit: but as they start at different hours from the same place, they are sometimes obliged to go part or nearly the whole of their voyage against the tide. The voyage has been accomplished in 24 hours; the tide being favourable, but against a moderate breeze of contrary wind +. "At first, owing to the novelty and apparent danger of the conveyance, the number of passengers was so very small that the only steam-boat then on the river could hardly clear her expenses: but the degree of success which attended that attempt soon commanded public confidence. The number of passengers which now go in those boats may seem incredible to those who have not witnessed it. Travelling by land has not only been nearly superseded, but the communication very greatly increased, owing to the cheapness and facility of the conveyance. Many days, in fine weather, from 500 to 600 have gone from Glasgow to Port-Glasgow and Greenock, and returned in the same day. One of the boats alone has been known to carry 247 *The first steam-boat in America was launched at New-York on the 3d of October, 1807, and began to ply on the river between that city and Albany, a distance of about 120 miles. The time which was allowed to the mail-coach to go between those towns was 34 hours, but owing to extraordinary exertion some of the coaches now run that distance in about 24 hours. at one time. The increase of travelling in consequence of navigation by steam, may be estimated by the number that went in the common passage boats before the introduction of this agent: at that time, the highest estimate even for summer did not much exceed 50 up and 50 down, and those generally of the lower class of the people. The number that then went by coaches may be thus estimated: four coaches up and four down, which might average six passengers each. "In the summer, the pleasure of the voyage and the beauty of the scenery attract multitudes; and the bathing-places below Greenock have, in consequence of the easy passage, been crowded beyond former example." "General Description.-A variety of modes of propelling steam-boats by the power of steam-engines have been projected, and many of them tried: but those on the Clyde have their machinery all constructed on one general plan; namely, that of paddle-wheels similar to under-shot water-mill wheels on each side of the vessel, which are put in motion by the steamengine. "Plate XXX. fig. 4. An elevation; a side view showing one of the paddle wheels. fig. 5. A plan, showing the extent of cabin floor. A. The fore or second cabin. BB. Space for the machinery. c. The iron chimney, serving also as a mast. EE. The steam-engine. s. Covering of paddle-wheels." STEEL-YARD, an instrument used for weighing goods, &c.; the theory of which was concisely stated in art. 138 of our first volume, and succeeded by a few remarks on its conveniences and inconveniences. In addition to what was there observed we may now state, that steel-yards, in the common purposes of commerce, have two advantages over balances. 1. That their axis of suspension is not loaded with any other weight than that of the merchandise, the constant weight of the apparatus itself excepted; while the axis of the balance, besides the weight of the instrument, sustains a weight double to that of the merchandise. 2. The use of the balance requires a considerable assortment of weights, which cause a proportional increase in the price of the apparatus, independently of the chances of error which it multiplies, and of the time employed in producing an equilibrium. These motives induced C. Paul, inspector of weights at Geneva, to employ his thoughts on the means of so far improving steel-yards, that, either in delicate operations of the arts, or in those of the same kind which are often so necessary in the practice of the physical sciences, these instruments might be substituted with advantage for common balances. In order that we may better explain in what the improvement of these steel-yards consist, it will be proper to point out what were the faults of the common ones. 1. There were none of them, in which the points of suspension were exactly in the prolongation of the line of the divisions of the beam; a circumstance which necessarily changed the relation between the arms of the lever, the power, and the resistance, according as the direction of the beam was changed from a horizontal position. We have seen steel-yards, in which a degree only of difference in the inclination of the beam produced the difference of more than a pound in the result. 2. When the shell, the beam, and weight, are made at hazard, a person who possesses a steel-yard cannot know when the instrument is deranged; and even an artist cannot repair it, but by repeated trials, and with a great loss of time. 3. The construction of the common steel-yards, which have a small and a large side, renders it necessary to invert them frequently; a laborious operation when these instruments are heavy, and which exposes the axes to the danger of damage by the effect of the shocks which that turning occasions. As these double sides render it necessary to have a beam very straight, in order that it may be less faulty, it readily bends, which is a new source of error; and, the face which bears the numbers being narrow in proportion, it is difficult to form on it numbers sufficiently visible. These inconveniences are all avoided by the construction of C. Paul, which presents, besides, several other advantages not possessed by the old steel-yards. 1. The centres of the movement of suspension, or the two constant centres, are placed on the exact line of the divisions of |