Like the other Cornish engineers, young Trevithick took an active part from the first in opposing the Birmingham patent, and he is said to have constructed several engines, with the assistance of William Bull (formerly an erector of Watt's machines), with the object of evading it. These engines are said to have been highly creditable to their makers, working to the entire satisfaction of the mine-owners. The issue of the Watt trial, however, which declared all such engines to be piracies, brought to an end for a time a business which would otherwise have proved a very profitable one, and Trevithick's partnership with Bull then came to an end. 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."