Plate I. Fig. 5, represents the arrangement of a double engine for a boat, with its cylinders in different positions. _a a a_, boilers; _b b_, tar-vessel; _c_, valve-box; _d_, cylinders in different positions; _e_, piston-rod; _f_, pitman; _h_, centre-piece; _i i_, shaft; _k_, valve; _l_, steam-pipe; _m_, escape-pipe; _n_, condensers; _t_, water-wheel; _v_, face of the valves; _x_, tar-fire. The frame, holding the cylinder (_d_) is, by its opposite sides, so hung as to revolve. To the end of the axis of one side, extended over the cylinder, is fixed the centre-piece (_h_) resembling a crank, from which the bar or pitman (_f_) communicates to the cross-piece of the piston-rod. On this same axis, but outside the frame, is placed two circular pieces, one of brass, the other of iron, (_k_) which we may call the valves. One is fixed on the axis, the other moves, and accompanies the frame and cylinder in its revolution; from it, at opposite sides, pipes lead the steam to each end of the cylinder. It has a smooth face, which applies, and is kept by springs close to that of its counterpart fixed on the said axis. Steam-pipes lead from the boilers through the counterpart into the moving valve. On the opposite side of the fixed piece the eduction-pipe (_o o_) leads to the condensers. The condensers (_p_) are upright vessels, two to each cylinder, connected at top by a sliding valve box, so that the steam enters them alternately. At bottom are two valves, kept closed by weights. A stream of water is injected into the condensers, which escapes by the bottom valves (_p p_) by which also the air is blown out, at every stroke, in the same manner the engine is cleared of air at first. There are also two cocks and cross-pipes seen, Plate III. Fig. 4, to change the steam from one side to the other of the valve, to give a reversed motion of the engine. The power is communicated to its object from the opposite side of the frame by the axis attached thereto, and supported on bearings. This axis (_i i_) may be of any length; may terminate in a crank or cog-wheel, or another cylinder (as here represented) may be attached thereto at right angles to the first, to co-operate and produce, at every moment, equal power. Plate II. Fig. 6. Profile of the above. _a a_, the boiler; _c_, valve; _d e g_, cylinder and frame; _f_, valve; _h h_, cog-wheels; _i_, cog-wheels to move the pumps; _k k_, condensers; _m m_, coverings in; _o o_, gas-fire flue. Fig. 1. _a_, steam-pipe; _b_, escape-pipe; _c_, fixed valve; _d_, moving valve; _e_, axis; _f_, a washer; _g_, section of frame; _h_, a washer; _i_, centre-piece; _l l_, steam-pipe; _k k_, springs to keep the valves together.