Mr Watt applied for letters patent in 1768, for "methods of lessening the consumption of steam, and consequently of fuel in the steam engine," which passed the seals in January, 1769. Besides the improvements, or rather inventions, already alluded to, this patent contained in its specification methods to employ the steam expansively upon the piston, and, where water was not plentiful, to work the engine by this force of steam only, by discharging the steam into the open air after it has done its office; and also methods of forming a rotatory steam engine. Thus was completed Watt's single reciprocating engine,
and while the patent was passing through the different stages an engagement was entered into between the inventor and Dr Roebuck of the Carron iron works, a man equally eminent for kindness of heart, ability, and enterprise. The terms of this agreement were, that Dr Roebuck, in consideration of his risk of capital, should receive two-thirds of tiie clear profits of the sale of the engines which they manufactured. Dr Roebuck at this time rented the large coal mines at Kinneil, near Borrowstownness, and under the superintendence of
Mr Watt an engine was erected at Kinneil house, the cylinder of which was made of block tin, being eighteen inches diameter. The action of this engine far surpassed even the sanguine expectations of the proprietors. Preparations
\vt-e accordingly made for the manufacture of the new steam engine; but the pecuniary difficulties in which Dr Roebuck became at this time involved, threw a check on the proceedings. From this period till the end of 1773, during which time, as we have seen, Mr Watt was employed in surveys, &c., little was done with the patent right obtained in 1769. About the end of the year 1773, while Mr Watt was engaged in his survey of the Caledonian canal, he received intimation from Glasgow of the death of his wife, who left him a son and a daughter.
His fame as an engineer had now become generally known, and about the commencement of 1774, he received an invitation from Mr Matthew Boulton, of the Soho foundery, near Birmingham, to enter into copartnership, for the manufacture of the steam engine. Mr Watt prevailed upon Dr Roebuck to sell his share of the patent right to Mr Boulton, and immediately proceeded to Birmingham, and entered on business with his new partner. This new alliance was not only exceedingly fortunate for the parties themselves, but forms an important era in the history of the manufactures of Great Britain. Few men were so well qualified as Boulton to appreciate the merits of Watt's inventions, or possessed of so much enterprise and capital to put them into operation. He had already established the foundery at Soho on a scale of magnificence and extent, not at that time elsewhere to be found; and the introduction of Watt made an incalculable addition to the extent and regularity of its operation.
The length of time and great outlay necessary for bringing the manufacture of steam engines to such a state as would yield a remuneration, was now apparent to Mr Watt, and he clearly saw that the few years of his patent which had yet to run, would not be by any means sufficient to yield an adequate return. Early, therefore, in 1774, he applied for an extension of his patent right, and by the zealous assistance of Drs Roebuck and Robiaon, he obtained this four years afterwards, the extension being granted for twenty-five years. The year following the first application for the extension of the patent, the manufacture of steam engines was commenced at Soho, under the firm Boulton, Watt, and Co. Many engines were made at this foundery, and licenses granted to miners in various parts of the country to use their engines, on condition that the patentees should receive a third part of the saving of coals of the new engine, compared with one of the same power on Newcomen's construction, AH idea
