boiler; but in this boiler a very ingenious mode is used, by which the necessity of the cocks his dispensed with. There are two cocks ii, which are placed the one considerably above, and the other as much below, the assumed level of the water; these cocks communicate with a vertical tube of glass j, of sufficient strength to endure the force of the steam. On the cocks ii, being opened, water enters into the lower cock, and steam into the upper one, and the pressure being the same in the boiler, the water stands at the same level, and thereby indicates at all times whether it be too high or too low, in the boiler.

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 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 forked end of the beams ee, 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 k k. These cranks are fixed to the main shaft, which rests upon the bearances 1 l, upon the arches m, which are bolted to the cross beam, as at î. The shafts are shewn 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 bends, represented by the lighter parts of the shading, 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 laying 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 2 s

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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 uu (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 condenser, 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.

In 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 steam-tight by a lid g screwed to it. On the upper side of the steam chest is a stuffing box, through which passes a turned rod for working the sliding valve h, which is represented in section.

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, as 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 present 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 b, and the open part of the valve, and so into the condenser; but suppose that the valve 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 used in the