As Cornwall was, however, now becoming well supplied with pumping-engines, it became necessary to open up new branches of business to keep the Soho manufactory in full work. With this object, Boulton became more and more desirous of applying the engine to the various purposes of rotary motion. In one of his visits to Wales, in 1781, he had seen a powerful copper-rolling mill driven by water, and when told that its defect was that it was liable to be stopped in summer during drought, he immediately asked--“Why not use our engine? It goes night and day, summer and winter, and is altogether unaffected by drought.” Immediately on his return home, he made a model of a steam rolling-mill, with two cylinders and two beams, connecting the power by a horizontal axis; and by the end of the year he had a steam forge erected at Soho on this plan. “It answers very well,” he wrote to Matthews, “and astonishes all the ironmasters; for, although it is a small engine, it draws even more steel per day than a large rolling-mill in this neighbourhood draws by water.” Mr. Wilkinson was so much pleased with it that he ordered one to be made on a large scale for the Bradley ironworks; and another was shortly after ordered for Rotherham. But the number of iron mills was exceedingly limited, and Boulton did not anticipate any large extension of business in that quarter. If, however, he could once get the rotary engine introduced as the motive power for corn and flour mills, he perceived that the demand would be considerable. Writing to Watt on the subject, he said, “When Wheal Virgin is at work, and all the Cornish business is in good train, we must look out for orders, as all our treaties are seemingly at an end, having none now upon the tapis. There is no other Cornwall to be found, and the most likely line for increasing the consumption of our engines is the application of them to mills, which is certainly an extensive field.”