with the number of parts, which were exposed to injury, prevented their successful adoption. Another method, upon a somewhat similar principle, is represented in the accompanying figure. The cranks a a are moved by the engine,

and turn with them the horizontal bar, to which are fixed the vertical paddles. By this method all the paddles are immersed in the water in a vertical position, and raised out of it in the like manner; but although the back-water is avoided by this method, yet it is obvious that another difficulty is encountered, of a more formidable nature; which is, that the motion of the paddles, in entering, is exceedingly slow, and probably slower than the speed at which the vessel passes through the water; so that, unless the speed be too great when the paddles move at their greatest velocity, namely, when the cranks are vertical, they must, at entering and leaving the water, considerably impede the motion of the boat. A method of keeping the paddles vertical, during the revolution, is described by Mr. Robertson Buchanan, in his "Treatise on propelling Vessels by Steam," which he thus explains :

"If two equal rings or circular lines in the same plane, or in planes parallel to each other, be conceived to revolve each upon its respective centre in its own plane, with one and the same uniform velocity, and in the same direction with regard to parts of the rings, or lines alike situated, and any point be taken in one of the lines or rings, and a right line to be drawn from that point, parallel to a line supposed to join the centres, until it meets the other ring or circle, then the right line so drawn will be equal to the line of distance between the centres, and will continue equal and parallel to that line of distance during the whole of every revolution so made."

y

9

The dotted circle and the black circle in the accompanying figure, denote the rings or circles mentioned in the theorem, and y and x denote their centres; the lines 1 a, parallel to, and equal to the line of distance of the centres will continue equal and parallel to that line of distance, in the position of 2 c, and 3 e, and 4 g, and all other positions into which the point 1 can be brought, during the uniform, equal, and similarly directed revolutions of the two circles. It will be evident on a little inspection, that this paddle wheel of Mr. Buchanan's is, (as he observed himself) liable to the objections stated to exist against

the last described apparatus, namely, that of impeding the speed of the boat, by its comparatively slow motion on entering and leaving the water. This fault, together with that of great complexity, and consequent liability to breakage, will probably preclude its successful adoption; although there have been many recent attempts to introduce it.

In the early constructed steam-boats only one steam cylinder was employed, but now it is the invariable custom to use two steam cylinders; each of which is made to work a crank upon the axle of the paddle wheels. The cranks are at right angles to each other, so that when one is passing the dead point, the other is exerting its utmost force. In America the engines are usually on the high-pressure plan, and the boilers as well as the principal part of the machinery upon deck. In British steam-vessels the engines are principally constructed on the low-pressure condensing principle, and the machinery all below deck. The latter circumstance renders it indispensable to diminish the height of the engines, and to transfer the working beams from above the cylinders to beneath them. To reduce the height also, the cylinders are made of greater diameter, in proportion to their length, than in land engines. A tolerably correct idea of the general arrangement of the machinery, as well as the various accommodations in a steam passage boat, will be afforded by the figures on the opposite page.

The upper figure represents a longitudinal and vertical section, from stem to stern, of a steam-vessel; and the lower figure a plan of the same, with the deck removed; similar letters in each figure refer to the corresponding parts.

a a are two boilers; b the chimney, leading from the flues of both the fires; e is the steam-pipe, only partly brought into view in the section, but its course is better seen in the plan, where it is shown to proceed from both the boilers into a single tube, which conveys it into another cross tube, that connects it to the two cylinders d d, by the intervention of the valve boxes ff. The air-pumps e e, are worked by the main beam, and the eccentric, for giving motion to the valves, is shown at g. The paddle-wheels h h, are usually attached to the main crank by a coupling-box, or toothed wheels, which enables the engineer to throw off either of the propelling wheels at pleasure; i, one of the paddle-boxes, seen only in the section. j is the fore-cabin, k the after-cabin, oo are staircases; il the framing of timber which supports a platform or deck (commonly called the gangway,) which nearly surrounds the hull of the vessel.

The American steamers are for the most part fitted up with more extensive and splendid accommodations than our own. The dining-room of The North America is described as being 150 feet in length, and to be capable of dining from 700 to 1000 passengers! The floors are covered with the finest carpets; the curtains of damask silk, and the ornamental work elaborately carved, and richly gilt. The walls are hung with the works of celebrated artists, &c. The fare from New York to Albany, including three meals, is only four dollars. It is usually performed (144 miles,) within twelve hours, including stoppages in the voyage at ten or twelve different places. There being no machinery below, the whole extent of the hull of the vessel is left open for those various commodious arrangements, which in reality constitute an American steamer into a grand floating hotel. The British steamers being, on the contrary, built to sustain the waves of the ocean, are differently constructed. A good example of the construction of steamers in this country is afforded by The United Kingdom packet, from London to Leith, which is usually performed in from 40 to 50 hours. She measures 148 feet in the keel, and the breadth of her beam is 45 feet. The accommodations for passengers are of the most elegant and convenient description. She is propelled by two engines of 100 horse power each, (constructed by Mr. Napier, of Glasgow,) which are considered as specimens of very superior workmanship. As these sorts of engines very nearly resemble each other, we have selected those of this vessel as illustrations of the mode in which steam-boat engines are usually constructed. The boilers to this engine we have already described under that head, pages 214, 215, Vol I.; we shall therefore confine our notice here to the engines only.

In the subjoined engraving, Fig. 1 represents an end view of the two engines, and Fig. 2, a side view of one of them. The letters refer to the same parts in

VOL. II.

5 c

each. The cylinders a a are of cast iron, and fixed to a framing, which is bolted to the bottom of the boat. The piston-rods b b, are keyed at the upper ends, to the cross heads cc; to the exterior ends of which are attached the connecting-rods d d. The lower ends of these connecting-rods are inserted in the fork end of the beams e e, which vibrate upon a shaft f, the bearances of which rest upon the top of the condenser g. In the same forks are inserted the ends of other connecting-rods h h, which are keyed at their upper ends to cross heads ii. In the centre of these cross-heads are bushes large enough to receive the rods jj, which extend to the crank pins of the cranks kk. These cranks are fixed to the main shaft, which rests upon the bearances 11, upon the arches m, which are bolted to the cross beam, as at n. The shafts are shown as broken off at the outer ends, but they extend to the outside of the paddle wheel.

The side beams e e, are not straight, but have two bands, represented by the lighter parts of the stading, the ends near the cylinder being therefore much farther apart than the opposite ends, so that they may take up as little room as possible, by lying close to the respective parts of the machinery. They are also forked at the end nearest the air-pump o, so as to admit the insertion of the pump-rods p, which are connected at their upper ends to the cross-head q, in a bush, in the centre of which is keyed the air-pump rod r. Connecting-rods s, are attached at t, to the side beams e, and at their upper ends to cross-heads, which are connected as at u u, (Fig. 1,) to two rods, which work the plungers of two feed-pumps v, for supplying the boiler. j is the apparatus for blowing through, previous to starting the engine. It consists of a cock, which opens or closes a communication between the steam-chest and condensers, by turning the handle. The rod and lever x, are for the purpose of regulating the quantity of injection water which enters into the condenser, by a pipe from the outside of the vessel, and can be increased and lessened in quantity, by turning a cock to which the rod x is attached. y is the hot-well, into which the condensing water is discharged from the air-pump. The feed-pumps are supplied with water from this hot-well, through the medium of a pipe, the overplus being discharged through the side of the vessel, by another pipe which is not seen. the steam chest 1, is contained the sliding-valve. For the purpose of explaining its principle, we shall here introduce a separate diagram, which may be taken as a representation of the best form in which it is constructed, though it varies somewhat in its relative position from that of the engine we now describe. The cylinder a, in the following figure, has two apertures b c, at top and bottom, to which are bolted and cemented the upright pipe d, having near its centre, or in any other convenient part, a broad face represented at e, in which are three oblong holes, the upper one running into the cylinder through b, and the lower one into the cylinder through c. The middle one communicates with a separate recess h, to which is attached a pipe, which forms a communication with the condenser. The steam chest f, is a rectangular box of cast iron, and has a pipe attached to it from the boiler; this chest is covered over and made steamtight by a lid g screwed to it. On the upper side of the steam chest is a stuffingbox, through which passes a turned rod for working the slide-valve h, which is represented in section.

In

This valve has a flat face, neatly ground to the surface e, sufficient to cover two of the holes of e, and twice the breadth of any one of the surfaces intervening between any of the holes in e. The valve is raised into a box from its open interior part, being of sufficient dimensions to cover, in its present situation, two of the passages e, and leave open a third, the bottom one in the present instance being open.

If steam were admitted into the steam chest whilst the valve was in its highest position, it could only enter into the cylinder through c, and consequently would cause the piston to ascend, whilst the air above it would be discharged through 6, and the open part of the valve, and so into the condenser. But suppose the valve to be depressed so as to cover the middle and lowest holes, then the steam from the boiler would have free communication with the upper side of the piston through b, which it would consequently force downwards, whilst the steam