With the introduction of his double-acting engine of 1782, Watt may be said to have perfected the vacuum engine, which a long line of inventors had been striving to produce. Despite, however, the immense superiority of Watt's low-pressure engine over that of Newcomen, the steam engine was as yet only in its infancy. On the expiration of Watt's patent in 1800 the steam engine entered upon a new career. The era of high-pressure steam and of steam locomotion commences from this date, and in connection with both these applications the name of Richard Trevithick occupies the foremost place. In 1800 Trevithick built a highly ingenious double-acting high-pressure engine, with a crank, for Cook's Kitchen mine, and this economical type of engine, known as a ‘puffer’ to distinguish it from the noiseless condensing engine, was soon in demand in Cornwall and South Wales for raising the ore and refuse from the mines.
As early as 1796 Trevithick had made models of steam locomotives, which were exhibited to friends at Camborne, and made to run on the table. The boiler and engine were in one piece; hot water was put into the boiler and a redhot iron was inserted into a tube beneath, thus causing steam to be raised and the engine set in motion. A model by Trevithick of a similar order, probably made in 1798, is now in the South Kensington Museum. The working of the crank in one of the mining or ‘whim’ engines of the Cook's Kitchen type suggested to Trevithick an improvement upon his toy model, and during 1800 and 1801 he was, at intervals, busy in modelling and designing a genuine steam carriage. Such a vehicle was completed by him on Christmas Eve, 1801, when it conveyed for a short experimental trip the first load of passengers ever moved by the force of steam. It was known locally as the ‘puffing devil’ or ‘Captain Dick's puffer,’ but apart from the difficulty experienced in keeping up the steam for any reasonable length of time, the roads about Redruth were execrably bad, and the engine met with several mishaps. Nevertheless, in January 1802, the inventor went up to London with his cousin Andrew Vivian, was interviewed by Count Rumford and Davy as to the possible utility of the new machine, and with some difficulty obtained a patent (dated 24 March 1802), the specification having been drawn up with the aid of Peter Nicholson [q. v.]
The introduction of the high-pressure principle as indicated in this patent gave increased power to steam, and Stuart would date the era of the locomotive from this discovery of Trevithick. The principle of moving a piston by the elasticity of the steam against the pressure only of the atmosphere had been described, it is true, by Leupold, and mentioned by Watt in one of his patents; but there is equally no doubt that Trevithick, by his rejection of Watt's fears as to the use of steam at high temperature, no less than by his ingenuity in the selection and arrangement of forms, gave the high-pressure engine for the first time a practical application. His only competitor in the construction of a practical high-pressure engine was another great mechanical genius, Oliver Evans of Philadelphia, who in 1804 built a steam wagon, the pioneer of the extended use of steam in America (cf. Stuart, Anecdotes of Steam Engines, ii. 461).
About 1759 John Robison [q. v.], when at Glasgow, had suggested to James Watt the use of steam for the moving of a wheel carriage, but the idea had been dropped. In 1770 Nicolas Joseph Cugnot, a native of Lorraine, constructed upon three wheels a ‘fardier mû par l'effet de la vapeur d'eau produite par le feu,’ a species of locomotive, which ran a mile in a quarter of an hour; but its tractive force was practically nil, and it was promptly voted a public nuisance (it is now to be seen in the Conservatoire des Arts et Métiers at Paris). A somewhat similar fate overtook a low-pressure locomotive built by Watt's ingenious assistant, William Murdock, in 1786. Murdock would have liked to pursue the experiment further, but it was strongly discountenanced by Watt as chimerical.
From where it was thus left Trevithick carried the locomotive a greater distance than any single man. In the early months of 1803 a second steam carriage of his design, built at Camborne, was exhibited in London, and made several successful trips in the suburbs. It had a cylinder 5½ inches in diameter, with a stroke of 2½ feet, and with thirty pounds of steam it worked fifty strokes a minute. The trials were brought to an end by the frame getting a twist, whereupon the engine was detached from the coach and applied to driving a mill for rolling hoop-iron. Trevithick's partners, Vivian and West, were disappointed by the lack of practical success, and experiments in steam road-carriages were postponed for many years.
Trevithick himself seems to have been in no wise depressed, for during the latter months of 1803, while employed in a general capacity as engineer at Pen-y-darran ironworks, near Merthyr Tydvil, he was engaged upon the first steam locomotive ever tried
