The following table given by Captain Ross will convey an idea of the comparative lengths of voyages made in steam boats and sailing vessels.
Having thus given a general and brief sketch of the progress of steam navigation, we shall proceed to describe the construction of a steam ship, and of the engine by which it is propelled.
The external form of a steam boat is shown in Plate DX. Fig. 4 ; and Fig. 5 represents the section of the two engines in the Royal George steam ship, as executed by Mr. Gutzmer, civil engineer, Edinburgh. At the two extremities of the two horizontal axles, A P, A' P', passing across the steam boat, are fixed the paddle wheels, one of which is shown at W W. The cylinders of the engines are placed behind the steam chests F, F', and by the alternate ascent and descent of' the piston rods B B, attached to the cranks C C', a rotatory motion is communicated to the hori zontal axles A P, A' P', and consequently to the pad dles NV W, which are fixed to them. The cranks which work the steam valves are shown at K lc'. The air pump E is wrought by the crank D, which is driven by the inner branch H of each of the cranks. The boiler G G extends quite across the ship. The top frame iiii of the engine, and the machinery are supported by the pillars h, h, h, h. The sides of the ship are shown at 1, /, 1, 1, the deck at m, nr, m, and the funnel at k.
As the object of the preceding figure is principally to convey an idea of the manner in which the steam engines are arranged on board of a steam-boat, we must refer to Fig. 6 for a distinct view in isometrical perspective of one of the engines for a boat, as arranged by Boulton and Watt. This arrangement, however, was adopted by Boulton and Watt, in com mon with others, from the engines erected on board the Clyde steam-boats. A section of a steam boat engine, but not exactly the same as that shown in Fig. 5, is shown in Fig. 7, and as we have put the same letters of reference to both, we shall describe them together, so as to give a perfect idea of the con struction of the most approved steam-boat engines. The steam from the boiler is introduced into the top or bottom of the cylinder A by the steam pipe S S, after passing through the slide valve already described in p. 423. When it has acted upon the piston, it
passes from the slide valve to the condenser B, where it is condensed into water by a rose jet in constant play. The air pump shown at C receives the con densed water from B, and forces the air and water into the cistern D, from which it flows out by a pipe. The reciprocating motion of the piston is conveyed to the crank by means of the beams or levers, one of which is shown at E 1' moving round G as an axis. These beams are connected with the T-piece L I., or cross head of the piston, by the side rods m n o p, forming part of !he parallel motion, the guiding bars of which arc N, N'. The working end of the lever E is united with the crank i II i' by the con nccting rod II II. The air pump C is also wrought by side rods c c connected with the beams E F, and the hot water pump from the same T•piece or cross head, The slide valve is on Murdoch's plan, and is moved by a wheel on the shaft I of the crank, with a sliding frame P, and it may also be moved by hand by means of the lever T, the slide rod being moved by slings from the arm R. The steam passes into the condenser by the valve 0, when the engine is set to work, and the air and water are driven into the cis tern D at the discharge valve.
Two of these engines are generally placed on board every steam boat, a passage being left between them, and space being reserved for working the fires between the cylinder and the boiler. The coals are kept in iron tanks in the engine room.
The weight of an engine of this kind of 40 horse power, with suitable duplicate parts, water, &c. is about 100 tons.
The steam-engine of Mr. Gurney, as applied to steam-boats, is so very unlike those in common use, that we have given a representation of it in Fig. 7, from the engraving published by Captain Ross. The figure represents it as placed betWeen the two decks of a vessel. Its boilers are exactly similar to those already described. (See p. 422, and Plate DIX.