that the non-conducting character of that material would have diminished condensation; but he found that such cylinders could not resist the continued action of the steam. This 1769 patent covered, as has been said, several heads of invention. The fifth head was for a rotary engine, of which the description was of the very haziest, and, as there were not any drawings attached to the specification of this patent, it would have been impossible from the information afforded by it for any workman to have constructed such a machine; and even could he have made it, it would not have worked, as Watt found out after repeated trials. Another head of invention was to lower the pressure of the steam by cooling it to a point not sufficient to cause condensation, and then to reheat it. Neither of these inventions ever came into practical use, and it is certainly a matter of surprise that, in the actions which ensued upon this patent, objection was not taken to the absolute absence of explanation as regards the fifth head of invention, the rotary engine. With Roebuck's assistance an engine with the separate condenser and air-pump was actually erected at Kinneil. The cylinder was eighteen inches diameter. This engine was tried on several occasions, but with no thoroughly definite result.
Dr. Roebuck having got into financial difficulties, the progress of the engine was impeded until, fortunately for Watt and for the world, Roebuck and Dr. Small in 1767 brought about the connection between Watt and Boulton. Subsequently Roebuck surrendered, on a proper payment, his interest in Watt's invention. It was then agreed, as so many of the fourteen years' life of the patent had expired without any remunerative result whatever, to apply to parliament to obtain an extension. In 1775 this act, which extended the patent until 1800, was passed, and in the same year the partnership with Boulton was effected. The experimental engine was removed from Kinneil to Soho, and was there put to work in such a manner as to demonstrate the merit of Watt's invention.
Inquiries from owners of Cornish mines began to be made as to the provision of the new engines. A very considerable business developed gradually in Cornwall, involving Watt's living in that county for lengthened periods extending over several years. This appears to have been a time of great distress to Watt. He disliked the roughness of the people; he was averse from all bargaining; he was in his usual bad health; and was away from all the scientific society he loved. In the result a large number of the improved pumping engines were put up, and were paid for on the fuel-saving terms already stated; but, whatever may have been the hoped-for eventual profits, the immediate result was the locking up of a large amount of capital, and it demanded all Boulton's indomitable energy and the exercise of his admirable business talents to carry the partnership through the time of trial. This Boulton, however, successfully accomplished, and, what is more, he encouraged his partner Watt, faint-hearted in all commercial matters, to hold up against their troubles. On 16 April 1781 he wrote to Watt in Birmingham: ‘I cannot help recommending it to you to pray morning and evening, after the manner of your countrymen (the Scotch prayer “The Lord grant us a gude conceit of ourselves”), for you want nothing but a good opinion and confidence in yourself and good health.’ It should have been stated that in the ‘Watt’ engine a cover was placed over the cylinder, the piston-rod working through a stuffing-box, and that the steam was at all times admitted to the upper side of the piston, its pressure replacing that of the atmosphere when the downward or working stroke of the piston was made, at which time the bottom of the cylinder was in connection with the condenser; that when the return stroke was to be made the condenser was shut off by an appropriate valve, and that another valve, called an ‘equilibrium valve,’ was opened, thereby establishing a connection between the upper and the under side of the piston, which, being then in equilibrium, could be drawn up by a counter-weight. Thus far the improved engine, like its predecessor (Newcomen's), was applied practically only for the raising of water; and where, as was so commonly the case, rotary motion was needed, recourse was had, if the work were beyond the power of horse gear, to the employment of a water-wheel to be driven by the water pumped by the engine. This was obviously an unsatisfactory operation, involving the cost of extra plant—plant demanding a considerable space—and involving also the diminished output of work due to the losses in the intermediate machine, the water-wheel. Watt therefore applied himself to obtain rotary motion from his reciprocating engine. The engine, being single-acting, did not lend itself well to the purpose; but it could be made to perform, to a considerable extent, as though it were double-acting by the expedient of largely increasing the counter-weight until it was equivalent to about one-half the total raising power of the piston. Watt applied himself to produce direct rotary motion from
