The engine used in steam-carriages is the high pres sure one of Trevithick, already described and repre sented iu Plate DIX. Fig. 4; but as this subject has now become one of national importance, we have given in Plate DXI. Fig. 5, a drawing of one of the most approved steam-carriages with its engine after Mr. T red gold.
Fig. 5 is a side elevation, and Fig. 6, a vertical section of this carriage, the same letters indicating the same parts in each. From the cylindrical boiler A, surrounded with the fire and flues, the steam passes into two large cylindrical reservoirs of steam II, II', of the same diameter. In these reservoirs are placed the engine cylinders G, G'. The parts II, are a re servoir of water not exposed to the pressure of the steam, but warmed by the flues and chimney so as to be heated previous to its being pumped into the boiler. For distributing the heat of the fuel over a large sur face there are two fire places with fire doors at B, B', which are fed with coals by hoppers from the boxes D, D', the doors being used only to clear the bars. The flues meet at the middle, the one from the fire B rising at F, Fig. 6, passing along the upper surface of the cylinder A round H at M, then round the end of the boiler, and returning on the opposite side to ascend the chimney in the division E'. The other flue pro ceeds in a similar manner but in an opposite course, and ascends at E; there are two apertures beneath each ash-pit C, C', for admitting air, and both of them should be provided with registers, so that those may be open, which either face a strong wind, or the di rection of the motion of the carriage when there is not sufficient wind. For the same reason the top of the chimney should have two mouths to assist the draught. The engine and boiler rest upon a frame supported by the axis; but in order to prevent the carriage from resting on three wheels, four spiral springs may be fixed on the boxes LL, and the cross heads must be connected to the piston rods, and all the bearings must be formed so as to accommodate the parts to the sink ing of one of the wheels. The pipe K carries the waste steam to the chimney, and there should be two safety valves, one locked in a box at J, and the other at J' for the use of the engine man.
In the year 1824, our late ingenious countryman Mr. David Gordon, to whom the arts are indebted for the invention of the portable gas lamp, took out a pa tent for improvements in the construction of steam carriages. His improvements relate to the machinery by which the power of the engine is to be applied to the ground, and the principal part of the contrivance consists of rods or propellers jointed to cranks situ ated at different angles upon the same axis, so that the extremities or feet of the propellers will act upon the ground in succession at a time when they are moving with the greatest velocity, or nearly so. The under surfaces of the feet of the propellers are curved, being described by a circle of about the same radius as the radius of the cranks which put them in motion, in order that the feet may accommodate themselves to the ground, particularly in the act of turning. Bristles, whalebone, or other pliable materials are fixed on the under surfaces of the curved feet of the propellers, as a substance to come into contact with the ground and take sufficient hold of it. During winter, when the ground is frozen, it is proposed to furnish the under surfaces of the feet with steel points projecting sufficiently to seize the ground. Notwith standing the ingenuity of these views, it is obvious that nothing can be gained by substituting feet for wheels, and that much power must be lost by the very action of the mechanism employed.
Great difficulties have yet to be overcome before steam-carriages can be used on common roads. On level and well formed lines there is no difficulty what ever, and the present steam carriages are perfectly ca pable of performing useful work under such cir cumstances; but unless some great invention is made by which we can increase the power of steam engines, without greatly increasing their weight, we can see no prospect of their being advantageously employed in any other way than upon rail-roads.
For farther information on this subject, see the works referred to in the two preceding articles.