While carrying on his business, Trevithick had frequent occasion to visit Mr. Harvey's iron foundery at Hayle, then a small work, but now one of the largest in the West of England, the Cornish pumping-engines turned out by Harvey and Co. being the very best of their kind. During these visits Trevithick became acquainted with the various members of Mr. Harvey's family, and in course of time he contracted an engagement with one of his daughters, Miss Jane Harvey, to whom he was married in November, 1797.
A few years later we find Trevithick engaged in partnership with his cousin, Andrew Vivian, also an engineer. They carried on their business of engine-making at Camborne, a mining town situated in the midst of the mining district, a few miles south of Redruth. Watt's patent-right expired in 1800, and from that time the Cornish engineers were free to make engines after their own methods. Trevithick was not content to follow in the beaten paths, but, being of a highly speculative turn, he occupied himself in contriving various new methods of employing steam with the object of economizing fuel and increasing the effective power of the engine.
From an early period he entertained the idea of making the expansive force of steam act directly on both sides of the piston on the high-pressure principle, and thus getting rid of the process of condensation as in Watt's engines. Although Cugnot had employed high-pressure steam in his road locomotive, and Murdock in his model, and although Watt had distinctly specified the action of steam at high-pressure as well as low in his patents of 1769, 1782, and 1784, the idea was not embodied in any practicable working engine until the subject was taken in hand by Trevithick. The results of his long and careful study were embodied in the patent which he took out in 1802, in his own and Vivian's name, for an improved steam-engine, and "the application thereof for driving carriages and for other purposes."
The arrangement of Trevithick's engine was exceedingly ingenious. It exhibited a beautiful simplicity of parts; the machinery was arranged in a highly effective form, uniting strength with solidity and portability, and enabling the power of steam to be employed with very great rapidity, economy, and force. Watt's principal objection to using high-pressure steam consisted in the danger to which the boiler was exposed of being burst by internal pressure. In Trevithick's engine, this was avoided by using a cylindrical wrought-iron boiler, being the form capable of presenting the greatest resistance to the expansive force of steam. Boilers of this kind were not, however, new. Oliver Evans, of Delaware, had made use of them in his high-pressure engines prior to the date of Trevithick's patent; and, as Evans did not claim the cylindrical boiler, it is probable that the invention was in use before his time. Nevertheless, Trevithick had the merit of introducing the round boilers into Cornwall, where they are still known as "Trevithick boilers." The saving in fuel effected by their use was such that in 1812 the Messrs. Williams, of Scorrier, made Trevithick a present of £300, in acknowledgment of the benefits arising to their mines from that source alone.
Trevithick's steam-carriage was the most compact and handsome vehicle of the kind that had yet been invented, and, indeed, as regards arrangement, it has scarcely to this day been surpassed. It consisted of a carriage capable of accommodating some half-dozen passengers, underneath which was the engine and machinery inclosed, about the size of an orchestra drum, the whole being supported on four wheels—two in front, by which it was guided, and two behind, by which it was driven. The engine had but one cylinder. The piston-rod outside the cylinder was double, and drove a cross-piece, working in guides, on the opposite side of the cranked axle to the cylinder, the crank of the axle revolving between the double parts of the piston-rod. Toothed wheels were attached to this axle, which worked into other toothed wheels fixed on the axle of the driving-wheels. The steam-cocks were opened and shut by a connection with the crank-axle; and the force-pump, with which the boiler was supplied with water, was also worked from it, as were the bellows to blow the fire and thereby keep up the combustion in the furnace.
The specification clearly alludes to the use of the engine on railroads as follows: "It is also to be noticed that we do occasionally, or in certain cases, make the external periphery of the wheels uneven by projecting heads of nails or bolts, or cross grooves or fittings to railroads where required, and that in cases of hard pull we cause a lever, belt, or claw to project through the rim of one or both of the said wheels, so as to take hold of the ground, but that, in general, the ordinary structure or figure of the external surface of those wheels will be found to answer the intended purpose."
The specification also shows the application of the high-pressure engine on the same principle to the driving of a sugar-mill, or for other purposes where a fixed power is required, dispensing with condenser, cistern, air-pump, and cold-water pump. In the year 1803, a small engine of this kind was erected after Trevithick's plan at Marazion, which worked by steam of at least 30 lbs. on the inch above atmospheric pressure, and gave much satisfaction.
The first experimental steam-carriage was constructed by Trevithick and Vivian in their workshops at Camborne in 1803, and was tried by them on the public road adjoining the town, as well as in the street of the town itself. John Petherick, a native of Camborne, who was alive in 1858, stated in a letter to Mr. Edward Williams that he well remembered seeing the engine, worked by Mr. Trevithick himself, come through the place, to the great wonder of the inhabitants. He says, "The experiment was satisfactory only as long as the steam pressure could be kept up. During that continuance Trevithick called upon the people to 'jump up,' so as to create a load on the engine; and it soon became covered with men, which did not seem to make any difference to the power or speed so long as the steam was kept up. This was sought to be done by the application of a cylindrical horizontal bellows worked by the engine itself; but the attempt to keep up the power of the steam for any considerable time proved a failure."
Trevithick, however, made several alterations in the engine which had the effect of improving it, and its success was such that he determined to take it to London and exhibit it there as the most recent novelty in steam mechanism. It was successfully run by road from Camborne to Plymouth, a distance of about ninety miles. At Plymouth it was shipped for London, where it shortly after arrived in safety, and excited considerable curiosity. It was run on the waste ground in the vicinity of the present Bethlehem Hospital, as well as on Lord's cricket-ground. There Sir Humphry Davy, Mr. Davies Gilbert, and other scientific gentlemen inspected the machine and rode upon it. Several of them took the steering of the carriage by turns, and they expressed their satisfaction with the mechanism by which it was directed. Sir Humphry, writing to a friend in Cornwall, said, "I shall soon hope to hear that the roads of England are the haunts of Captain Trevithick's dragons—a characteristic name." After the experiment at Lord's, the carriage was run along the New-road, and down Gray's-Inn Lane, to the premises of a carriage-builder in Long Acre. To show the adaptability of the engine for fixed uses, Trevithick had it taken from the carriage on the day after this trial and removed to the shop of a cutler, where he applied it with success to the driving of the machinery.
The steam-carriage shortly became the talk of the town, and the public curiosity being on the increase, Trevithick resolved on inclosing a piece of ground on the site of the present Euston station of the London and Northwestern Railway, and admitting persons to see the exhibition of his engine at so much a head. He had a tram-road laid down in an elliptical form within the inclosure, and the carriage was run round it on the rails in the sight of a great number of spectators. On the second day another crowd collected to see the exhibition, but, for what reason is not known, although it is said to have been through one of Trevithick's freaks of temper, the place was closed and the engine removed. It is, however, not improbable that the inventor had come 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.