[Illustration: ENTRANCE TO COSGARNE HOUSE.]
[Illustration: THE ‘WAGGON AND HORSES,’ HANDSWORTH.]
WATT AGAIN VISITS CORNWALL--INVENTION OF THE ROTARY MOTION--THE PATENT RIGHT AGAIN ASSAILED.
Watt’s presence being much wanted in Cornwall, he again proceeded thither, accompanied by his wife and family, and arrived at Cosgarne towards the end of June, 1781. He found that many things had gone wrong for want of the master’s eye, and it was some time before he succeeded in putting affairs in order. The men had been neglecting their work, “going a-drinking.” Cartwright had “contracted a fever in his working arm, and been swallowing ale for a cure,” until he heard Watt had come, when the fever left him. Mrs. Watt also found occasion to complain of sundry little grievances, and favoured Boulton with a long catalogue of them. Gregory and Jessy had caught cold on the journey, and workmen were hammering about the house making repairs. There was, however, one gleam of brightness in her letter: “James’s spirits were surprisingly mended since his arrival.”
Watt was a most voluminous correspondent. He wrote Boulton several times a week great folio sheets, written close, in small hand. The letters must have occupied much of his time to write, and of Boulton’s to read. The latter, seeing his partner’s tendency to indulge in “worrit” about petty troubles, advised him in a kindly spirit not to vex himself so much about such matters, but to call philosophy to his aid. Why should he not occupy some of his spare time in writing out a history of all his steam-engine contrivances, to be dedicated to Sir Joseph Banks, and published in the ‘Transactions of the Royal Society’? But Watt was extremely averse to writing anything for publication, and the suggestion was not acted on. Then, knowing Watt’s greatest pleasure to be in inventing, Boulton in a subsequent letter advised him to take up afresh, and complete a plan which they had often discussed, of producing rotary motion, by which the engine might be applied to work mills and drive machinery.
Watt had from the first regarded the employment of the steam-engine in producing continuous rotary motion as one of its most useful applications, and with this object he invented his original wheel-engine. No steps were taken to introduce the invention to practical use; but it occurred to Watt that the same object might be better effected by employing the ordinary engine for the purpose, with certain modifications.[202] The subject had partially occupied his attention during his first visit to Cornwall; for we find him writing Boulton from Chacewater, in 1779, “As to the circular motion, I will apply it as soon as I can, but foresee that I shall be very busy shortly, and much out of doors.” On his subsequent return to Birmingham, after frequent conferences with his partner on the subject, he proceeded to prepare a model, in which he made use of a crank connected with the working beam of the engine to produce the rotary motion. There was no originality in the employment of the crank, which was an expedient that Watt had long before made use of.[203] The crank was, indeed, one of the most common of mechanical appliances. It was in daily use in every spinning-wheel, in every grindstone turned by hand, in every turner’s and knife-grinder’s foot-lathe, and in every potter’s wheel. It was one of the commonest, as it must have been one of the oldest, of mechanical expedients. “The true inventor of the crank rotative motion,” said Watt, “was the man who first contrived the common foot-lathe: applying it to the engine was like taking a knife to cut cheese which had been made to cut bread.”