In the case of steam carriages used upon rail-roads, the structure of one is so dependent upon the other, that the former may be regarded as the moving, and the latter the stationary part, of the same machine. Whether the distinction thus attempted to be drawn is not in some degree applicable to both classes of locomotives, might be disputed; but there are other marked differences between them, which have induced us to treat them separately. The common road locomotives require to perfect them a higher degree of mechanical still than those on the rail; because they have not, like the latter, a level and unyielding surface to roll upon, but one that is full of asperities, and easily penetrable, hence increasing in a great degree the difficulties of construction. The former, likewise, now belong to a history of the past; while the latter form the glories of the present day. We therefore refer the reader to the Article Railway, for all locomotives that are designed for that species of way.
The merit of the first suggestion of steam carriages has been attributed to various individuals; but the probability is, that the idea of applying the steam engine for the purpose of locomotion is coeval almost with its first invention. Thus Savery from having considered its possibility, and Dr. Robison for having suggested it to Watt, have by some been regarded as the inventors. Mr. Watt, however, never built a steam engine; and it is said that he retained up to the period of his death, the most rooted prejudices against the use of high steam. Indeed, he says himself, " I soon relinquished the idea of constructing an engine on this principle, from being sensible it would be liable to some of the objections against Savery's engines, viz. the danger of bursting the boiler, and that a great part of the power of the steam would be lost, because no vacuum was formed to assist the descent of the piston." It was, however, the sagacity of two Cornish engineers, Trevithick and Vivian, which enabled them to perceive in the excessive force exerted by high steam, (and which alarmed Watt,) that very power which was indispensable to the propulsion of locomotive carriages; as it dispensed with the use of a condenser, and all its cumbrous appendages.
Previous to the year 1802, animal power was the only one known or in use for the moving of carriages; at that period, the above mentioned engineers obtained a patent for an improved steam engine, which was the first of the high pressure kind, and is thus characterized by the eloquent Mickleham. "It exhibits in construction the most beautiful simplicity of parts, the most sagacious selection of appropriate forms, their most convenient and effective arrangement and connexion; uniting strength with elegance; the necessary solidity with the greatest portability; possessing unlimited power with a wonderful pliancy to accommodate it to a varying resistance: it may indeed be called "The Steam Engine." The specification of the patent, after describing this engine, proceeds to show its application, "to give motion to wheel carriages of every description," by suitable drawings and explanations. From a copy of that document we derive the following account of the first steam carriage which was constructed.
Thevithick And Vivian's Steam Carriage
Fig. 1, is a vertical section, and Fig. 2, a plan, showing the principal arrangements of the first steam carriage. "At b b, is the case, having therein the boiler, with its fire place and flues. At p q, is the piston rod, forked to admit the end of the crank r; the said rod drives a cross piece at q backward and forward between guides; and this cross-piece, by means of the bar o. R, gives motion to the crank with its fly f, and to two wheels t t upon the crank axis, which lock into two correspondent wheels u upon the naves of the large wheels of the carriage itself. The wheels t are fixed upon round sockets, and receive their motion from a striking box or bar s x, which acts upon a pin in each wheel; s y are two handles, by means of which either of the striking boxes s x can be thrown out of gear, and the correspondent wheel w by that means diaconnected with the first mover, for the purpose of turning short, or admitting a backward motion of that wheel when required; but either of the wheels w, in case of turning, can be allowed considerably to overrun the other without throwing six out of gear, because the pin can go very nearly round in the forward motion before it will meet with any obstruction.
The wheels u are most commonly fixed upon the naves of the carriage-wheels w, by which means a revolution of the axis itself becomes unnecessary, and the outer ends of the said axis may consequently be set to any obliquity, and the other part fixed or bended, as the objects of taste or utility may demand. The fore-wheels are applied to direct the carriage by means of a lever h; and there is a check lever which can be applied to the fly, in order to moderate the velocity of progression when going down hill. In the vertical section is shown a springing lever, having a tendency to fly forward. Two levers of this kind are duly and similarly placed near the middle of the carriage, and each of them is alternately thrown back by a short bearing lever upon the crank axis, which sends it home into a catch at the end, and afterwards releases it when the bearing lever comes to press upon v, in which case the springing lever flies back. A cross bar, or double handle is fixed upon the upright axis of the cock, from each end of which said cross bar proceeds a rod p q, which is attached to a stud q, that forms part of the spring lever.