The numerous MS. books left by Boulton show the care with which he made his experiments, and the scrupulousness with which he recorded the results. Copies of his observations and experiments on boilers were sent to Watt, to be entered by him in “the calculation book,” in which was recorded the tabulated experience of the firm. Boulton was also an excellent mechanical draughtsman, as appears from his tablets, which contain a number of beautifully executed drawings of engines and machinery, with very copious and minutely-written instructions for erecting them. Some of the drawings of sugar-mills are especially well executed, and delicately coloured. A rough sketch is given in one of the books, with a written explanation in Boulton’s hand, of a mode of applying power in taking canal-boats through tunnels. It consists of an engine-boat, with toothed claws attached to it for the purpose of catching metal racks fastened along the sides of the tunnel, such being his design for working boats upon canals. While in Cornwall, he occupied his evenings in drawing sections of various mines, showing the adits, and the method of applying the pumping machinery, to which were also added numerous elaborate calculations of the results of engine working. He also continued to devise improvements in the construction and working of the steam-engine, on which subject he exchanged his views with Watt at great length. In one of his letters he says: “I like your plan of making all the principal wearing parts of tempered steel, and the racks of best Swedish iron, with the teeth cut out. Query: Would it not be worth while to make _a machine_ for dividing and cutting the teeth in good form out of sectors? The iron would be less strained by that mode of cutting.” At other times, when the steam-engine subject seemed exhausted, he proceeded with the designing of road-carriages, in which he was an adept, filling a quarto drawing-book, entitled ‘Thoughts on Carriages,’ with sketches of different kinds of vehicles, some in pencil and Indian ink, and others in colours, beautifully finished. Such were the leisure employments of this indefatigably industrious man. [Illustration: ENTRANCE TO COSGARNE HOUSE.] [Illustration: THE ‘WAGGON AND HORSES,’ HANDSWORTH.] CHAPTER XV. WATT AGAIN VISITS CORNWALL--INVENTION OF THE ROTARY MOTION--THE PATENT RIGHT AGAIN ASSAILED.