for other purposes." * The steam-carriage built by Trevithick on this patent presented the appearance of an ordinary stage-coach on four wheels. It 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. It is also worthy of note, that 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.

This was the first successful high-pressure engine 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 the pressure acted only on one side of the piston. In Trevithick and Vivian'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 was then opened between the boiler and the upper side of the piston, which was pressed downwards, and the steam again allowed to escape into the atmosphere. 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 first steam-carriage adapted for actual use on common roads, was, on the whole, tolerably successful. It excited

* The number of the patent in the Record of Patents Office is 2599.

considerable interest in the remote district, near to the Land's End, where it had been constructed. 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, with a view, if possible, to its practical adoption for the purpose intended. In furtherance of this object, they set out with the locomotive to Plymouth, whence a sea-captain, named Vivian, was to convey it in his vessel to town. Coleridge relates, that whilst the vehicle was proceeding along the road towards the port, at the top of its speed, and had just carried away a portion of the rails of a gentleman's garden, Andrew Vivian descried ahead of them a closed toll-gate, and called out to Trevithick, who was behind, to slacken speed. He immediately shut off the steam; but the momentum was so great, that the carriage proceeded some distance, coming dead up, however, just on the right side of the gate, which was opened like lightning by the toll-keeper. "What have us got to pay here?" asked Vivian. The poor toll-man, trembling in every limb, his teeth chattering in his head, essayed a reply 99 "Na-na-na-na"What have us got to pay, I say? "No-noth-nothing to pay! My de-dear Mr. Devil, do drive on as fast as you can! nothing to pay!"

The carriage safely reached the metropolis, and was there 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 the machine; but Trevithick, in one of his odd freaks, shut up the place, and shortly after removed the engine. While in the metropolis, he secured the support of Lord Stanhope, Davies Gilbert, and other distinguished men. Sir Humphry Davy took much interest in the invention of his countryman, and, writing to his friend David Giddy, in

Cornwall, shortly after the machine had reached town, he said, "I shall hope soon to hear that the roads of England are the haunts of Captain Trevithick's dragons - a characteristic name." It was felt, however, that the badness of the English roads at the time rendered it next to impossible to bring the steam carriage into general use; so that, after having been successfully exhibited as a curiosity, it was abandoned by Trevithick as a practical failure.

In the year following the exhibition of the steam-carriage, 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 proceeded to construct his second or railway locomotive. The idea, however, was not entirely new to him; for although his first steam-carriage had been constructed with a view to its employment on common roads, the specification of his patent distinctly alludes to the application of his engine to travelling on railroads. In 1804 he proceeded to construct a locomotive after an improved plan for this special purpose; and in the course of the same year it was completed, and tried on the Merthyr Tydvil Railway in South Wales. On the occasion of its first trial, the engine succeeded in dragging after it several waggons containing ten tons of bar-iron, at the rate of about five miles an hour. The boiler of this engine was cylindrical, flat at the ends, and constructed of cast-iron. The furnace and flue were inside the boiler, within which the single cylinder, of eight inches in diameter, and four feet six inches stroke, was immersed upright. 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. 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 in (1815) he took out a patent which included a method of urging the fire by means of fanners.

Although the locomotive tried upon the Merthyr Tydvil Railway succeeded in drawing a considerable weight, and travelled at a fair speed, it nevertheless proved, like the first steam-carriage, a practical failure. It was never employed to do regular work, but was abandoned after a few experiments. Its jolting motion champed up the cast-iron road, which was little calculated to bear so heavy a weight, though it was very light as compared with modern engines,—and it was consequently dismounted from its wheels, and the engine was subsequently fixed and used to pump one of the largest pumps on the mine, for which work it was found well adapted.

Trevithick was satisfied with merely making a few experiments with his steam-carriage and engine; and being a volatile genius, fond of new projects, he seems to have thought no more of the locomotive, but left it to take care of itself. Yet his machine, although unfitted for actual work, was a highly meritorious production, and its invention may be said to constitute an important link in the history of the mechanism of the steam-engine.

Trevithick having abandoned the locomotive for more promising schemes, no further progress was made with it for

some years. An imaginary difficulty seems to have tended, amongst other obstacles, to prevent its adoption and improvement. This was the supposition that, if any heavy weight were placed behind the engine, the "grip" or "bite" of the smooth wheels of the locomotive upon the equally smooth iron rail, must necessarily be so slight that the wheels would slip round upon the rail, and, consequently, that the machine would not make any progress. Hence Trevithick, in his patent, recommended that the periphery of the driving-wheels should be made rough by the projection of bolts or crossgrooves, so that the adhesion of the wheels to the road might be secured. This plan was adopted in Trevithick's engine tried on the Merthyr Tydvil Railway, and its progress must therefore necessarily have been a succession of jolts, very trying to the cast-iron plates of the colliery tram-road.

Following up the presumed necessity for a more effectual adhesion between the wheels and the rails than that presented by their mere smooth contact, Mr. Blenkinsop, of Leeds, in 1811, took out a patent for a racked or tooth-rail laid along one side of the road, into which the toothedwheel of his locomotive worked as pinions work into a rack. The boiler of his engine was supported by a carriage with four wheels without teeth, and rested immediately upon the axles. These wheels were entirely independent of the working parts of the engine, and therefore merely supported its weight on the rails, the progress being effected by means of the cogged wheel working into the cogged-rail. The engine had two cylinders instead of one, as in Trevithick's engine. The invention of the double cylinder was due to Matthew Murray, of Leeds, one of the best mechanical engineers of his time, Mr. Blenkinsop, who was not himself a mechanic, having consulted him as to all the practical arrangements of his locomotive. The connecting-rods gave the motion to two pinions by cranks at right angles to each other; these pinions