Watt, soon after perfecting his model, formed a partnership with Dr. Roebuck, then of the Carron iron-works, for theconstruction of engines on a Scale adapted, to practical uses; and a model was erected at Kinneil, near Borrowstounness, where Dr. Roebuck then lived. But Roebuck got into difficulties; and nothing further was done until, in 1773, Watt entered into a partnership with Matthew Boulton of Soho, near Birmingham, when, Roebuck's interest having been repurchased, the manufacture of the new engine was commenced at the Soho iron-works. A patent for his invention had been taken by Watt in 1769. He got from parliament a prolongation of his patent for 25 years in 1775.
The advantages of the new engine were in no long time found out by the proprietors of mines; and it soon superseded Neweomen's machine as a pumping-engine. Watt afterward made numerous improvements in its construction (for the most important of which see STEAM-ENGINE); and in conduction with his partner Boulton, lie immensely improved the quality of the workmanship employed in building engines and other machines. In the years 1781, 1782, 1784, 1785, he obtained patents fora series of inven tions—among them the sun-and-planet motion, the expansive principle, the double engine, the parallel motion, and the smokeless furnace, of most of ?which the chief pur pose was to make steam-pressu•e available for turnipg machinery in mills. The accom plishment of this—extending the application of the .new power to the arts—was of scarcely inferior importance to the invention of the steam-engine itself. The first con trivance invented by Watt for this purpose was lost to him through the treachery of a mechanic, who had been employed in making the model, who sold it to a manufacturer named Prickards, who got a patent for it for himself. The application to the steam
engine of the governor (see STEAM-ENGINE) was Watt's crowning improvement. He made numerous inventions unconnected with the steam-engine, several of which he patented, but they are all of minor importance.
He retired from business in the year 1800, giving up to his two sons his interest in the extensive and prosperous business which Boulton had created at Soho. He died at Heathfield in Staffordshire, on 'Aim 25, 1819, in his 84th year. Watt was twice mar ried: first in 1763, to his cousin, Miss Miller; and a second time shortly after his removal to Birmingham, to a Miss M'Gregor of Glasgow. He had a most extensive and accurate knowledge of the physical sciences—to several of which he made important contributions—and an almost unsurpassed fund of general information. (His claims to be considered the discoverer of the composition of water are considered in the article WATER.) He was elected a fellow of the Royal society of Edinburgh in 1784; a fellow of the Royal society of London in 1785; a corresponding member of the Batavian society in 1787; and in 1808, a corresponding member, and afterward a foreign member, of the institute of France. The university of Glasgow conferred on him the degree of LL.D. in 1806. His statue, the funds for which had been raised by a public, and almost a national subscription, was erected in Birmingham in 1824:- and his statue is now to be seen in the streets of many of our larger towns. The honor paid to his memory and to himself in his later years appear to have been deserved by his personal qualities, no less than by the immeasurable benefits which his inventive talents have conferred upon the human race.