July, 1781, Watt had finished his studies, went to Penryn, and swore he had "invented certain new methods of applying the vibrating or reciprocating motion of steam or fire engines to produce a continued rotation or circular motion round an axis or centre, and thereby to give motion to the wheels of mills or other machines." Watt proceeded to work out the plan of the rotary engine, stimulated by numerous inquiries for steam engines for driving all kinds of mills. He found that "the people in London, Manchester and Birmingham are steam-mill mad." During many long years of trial with their financial troubles, inferior and drunken workmen, disappointing engines, Cornish mine-owners to annoy him, it is highly probable that Watt only found relief in retiring to his garret to gratify his passion for solving difficult mechanical problems. We may even imagine that from his serious mission--the development of the engine--which was ever present, he sometimes flew to the numerous less exhausting inventions for recreation, as the weary student flies to fiction. His mind at this period seems never to have been at rest. His voluminous correspondence constantly reveals one invention after another upon which he was engaged. A new micrometer, a dividing screw, a new surveying-quadrant, problems for clearing the observed distance of the moon from a star of the effects of refraction and parallax, a drawing-machine, a copying-machine for sculpture--anything and everything he used or saw seems immediately to have been subjected to the question: "Cannot this be improved?" usually with a response in the affirmative.