The idea was next taken up by Murdock’s pupil, Richard Trevithick, who resolved on building a steam-carriage adapted for common roads as well as railways. He took out a patent to secure the right of his invention in 1802. Andrew Vivian, his cousin, joined with him in the patent—Vivian finding the money, and Trevithick the brains. The steam-carriage built on this patent presented the appearance of an ordinary stage-coach on four wheels. The engine had one horizontal cylinder, which, together with the boiler and the furnace-box, was placed in the rear of the hind axle. The motion of the piston was transmitted to a separate crank-axle, from which, through the medium of spur-gear, the axle of the driving-wheel (which was mounted with a fly-wheel) derived its motion. The steam-cocks and the force-pump, as also the bellows used for the purpose of quickening combustion in the furnace, were worked off the same crank-axle.
John Petherick, of Camborne, has related that he remembers this first English steam-coach passing along the principal street of his native town. Considerable difficulty was experienced in keeping up the pressure of steam; but when there was pressure enough, Trevithick would call upon the people to “jump up,” so as to create a load upon the engine. It was soon covered with men attracted by the novelty, nor did their number seem to make any difference in the speed of the engine so long as there was steam enough; but it was constantly running short, and the horizontal bellows failed to keep it up.
This road-locomotive of Trevithick’s was one of the first high-pressure working engines constructed on the principle of moving a piston by the elasticity of steam against the pressure only of the atmosphere. Such an engine had been described by Leopold, though in his apparatus it was proposed that the pressure should act only on one side of the piston. In Trevithick’s engine the piston was not only raised, but was also depressed by the action of the steam, being in this respect an entirely original invention, and of great merit. The steam was admitted from the boiler under the piston moving in a cylinder, impelling it upward. When the motion had reached its limit, the communication between the piston and the under side was shut off, and the steam allowed to escape into the atmosphere. A passage being then opened between the boiler and the upper side of the piston, which was pressed downwards, the steam was again allowed to escape as before. Thus the power of the engine was equal to the difference between the pressure of the atmosphere and the elasticity of the steam in the boiler.
This steam-carriage excited considerable interest in the remote district near the Land’s End where it had been erected. Being so far removed from the great movements and enterprise of the commercial world, Trevithick and Vivian determined upon exhibiting their machine in the metropolis. They accordingly set out with it to Plymouth, whence it was conveyed by sea to London.
The carriage safely reached the metropolis, and excited much public interest. It also attracted the notice of scientific men, amongst others of Mr. Davies Gilbert, President of the Royal Society, and Sir Humphry Davy, both Cornishmen like Trevithick, who went to see the private performances of the engine, and were greatly pleased with it. Writing to a Cornish friend shortly after its arrival in town, Sir Humphry said: “I shall soon hope to hear that the roads of England are the haunts of Captain Trevithick’s dragons—a characteristic name.” The machine was afterwards publicly exhibited in an enclosed piece of ground near Euston Square, where the London and North-Western Station now stands, and it dragged behind it a wheel-carriage full of passengers. On the second day of the performance, crowds flocked to see it; but Trevithick, in one of his odd freaks, shut up the place, and shortly after removed the engine. It is, however, probable that the inventor came to the conclusion that the state of the roads at that time was such as to preclude its coming into general use for purposes of ordinary traffic.
While the steam-carriage was being exhibited, a gentleman was laying heavy wagers as to the weight which could be hauled by a single horse on the Wandsworth and Croydon iron tramway; and the number and weight of waggons drawn by the horse were something surprising. Trevithick very probably put the two things together—the steam-horse and the iron-way—and kept the performance in mind when he proceeded to construct his second or railway locomotive. The idea was not, however, entirely new to him; for, although his first engine had been constructed with a view to its employment upon common roads, the specification of his patent distinctly alludes to the application of his engine to travelling on railroads. Having been employed at the iron-works of Pen-y-darran, in South Wales, to erect a forge engine for the Company, a convenient opportunity presented itself, on the completion of this work, for carrying out his design of a locomotive to haul the minerals along the Pen-y-darran tramway. Such an engine was erected by him in 1803, in the blacksmiths’ shop at the Company’s works, and it was finished and ready for trial before the end of the year.
The boiler of this second engine was cylindrical in form, flat at the ends, and made of wrought iron. The furnace and flue were inside the boiler, within which the single cylinder, eight inches in diameter and four feet six inches stroke, was placed horizontally. As in the first engine, the motion of the wheels was produced by spur gear, to which was also added a fly-wheel on one side, to secure a rotatory motion in the crank at the end of each stroke of the piston in the single cylinder. The waste steam was thrown into the chimney through a tube inserted into it at right angles; but it will be obvious that this arrangement was not calculated to produce any result in the way of a steam-blast in the chimney. In fact, the waste steam seems to have been turned into the chimney in order to get rid of the nuisance caused by throwing the jet directly into the air. Trevithick was here hovering on the verge of a great discovery; but that he was not aware of the action of the blast in contributing to increase the draught and thus quicken combustion, is clear from the fact that he employed bellows for this special purpose; and at a much later date (1815) he took out a patent which included a method of urging the fire by means of fanners. [70]
At the first trial of this engine it succeeded in dragging after it several waggons, containing ten tons of bar-iron, at the rate of about five miles an hour. Rees Jones, who worked at the fitting of the engine, and remembers its performances, says, “She was used for bringing down metal from the furnaces to the Old Forge. She worked very well; but frequently, from her weight, broke the tram-plates and the hooks between the trams. After working for some time in this way, she took a load of iron from Pen-y-darran down the Basin-road, upon which road she was intended to work. On the journey she broke a great many of the tram-plates, and before reaching the basin ran off the road, and had to be brought back to Pen-y-darran by horses. The engine was never after used as a locomotive.” [71]
It seems to have been felt that unless the road were entirely reconstructed so as to bear the heavy weight of the locomotive—so much greater than that of the tram-waggons, to carry which the original rails had been laid down—the regular employment of Trevithick’s high-pressure tram-engine was altogether impracticable; and as the owners of the works were not prepared to incur so serious a cost, it was determined to take the locomotive off the road, and employ it as an engine for other purposes. It was accordingly dismounted, and used for some time after as a pumping-engine, for which purpose it was found well adapted. Trevithick himself seems from this time to have taken no further steps to bring the locomotive into general use. We find him, shortly after, engaged upon schemes of a more promising character, abandoning the engine to other mechanical inventors, though little improvement was made in it for several years. An imaginary difficulty seems to have tended, amongst other obstacles, to prevent its adoption; viz., the