At a very early period, while experimenting at Kinneil, he had formed the idea of working steam expansively, and altered his model from time to time with that object. Boulton had taken up and continued the experiments at Soho, believing the principle to be sound and that great economy would attend its adoption. The early engines were accordingly made so that the steam might be cut off before the piston had made its full stroke, and expand within the cylinder, the heat outside it being maintained by the expedient of the steam-case. But it was shortly found that this method of working was beyond the capacity of the average engineman of that day, and it was consequently given up for a time. “We used to send out,” said Watt to Robert Hart, “a cylinder of double the size wanted, and cut off the steam at half stroke. This was a great saving of steam so long as the valves remained as at first; but when our men left her to the charge of the person who was to keep her, he began to make or try to make improvements, often by giving more steam. The engine did more work while the steam lasted, but the boiler could not keep up the demand. Then complaints came of want of steam, and we had to send a man down to see what was wrong. This was so expensive that we resolved to give up the expansion of the steam until we could get men that could work it, as a few tons of coal per year was less expensive than having the work stopped. In some of the mines a few hours’ stoppage was a serious matter, as it would cost the proprietor as much as 70_l._ per hour.”[156] The principle was not, however, abandoned. It was of great value and importance in an economical point of view, and was again taken up by Watt and embodied in a more complete form in a subsequent invention. Since his time, indeed, expansive working has been carried to a much farther extent than he probably ever dreamt of, and has more than realised the beneficial results which his sagacious insight so early anticipated. [156] Robert Hart’s ‘Reminiscences of James Watt,’ cited above. CHAPTER XIII. WATT IN CORNWALL--INTRODUCTION OF HIS PUMPING-ENGINES. The Cornish miners continued baffled by their attempts to get rid of the water which hindered the working of their mines. The Newcomen engines had been taxed to the utmost, but were unable to send them deeper into the ground, and they were accordingly ready to welcome any invention that promised to relieve them of their difficulty. Among the various new contrivances for pumping water, that of Watt seemed to offer the greatest advantages; and if what was alleged of it proved true--that it was of greater power than the Newcomen engine, while its consumption of fuel was much less,--then it could not fail to prove of the greatest advantage to Cornish industry.