Such were some of Watt's by-products. His recreation, if found at all, was found in change of occupation. We read of no idle days, no pleasure trips, no vacations, only change of work. Rumors of new inventions of engines far excelling his continued to disturb Watt, and much of his time was given to investigation. He thought of a caloric air engine as possibly one of the new ideas; then of the practicability of producing mechanical power by the absorption and condensation of gas on the one hand and by its disengagement and expansion on the other. His mind seemed to range over the entire field of possibilities. The Hornblower engine had been heralded as sure to displace the Watt. When it was described, it proved to be as Watt said, "no less than our double-cylinder engine, worked upon our principle of expansion. It is fourteen years since I mentioned it to Mr. Smeaton." Watt had explained to Dr. Small his method of working steam expansively as early as May, 1769, and had adopted it in the Soho engine and also in the Shadwell engine erected in that year. We have seen before that Watt had to retrace his steps and abandon for a time in later engines what he had before ventured upon. The application of steam for propelling boats upon the water was, at this time (1788), attracting much attention. Boulton and Watt were urged to undertake experiments. This they declined to entertain, having their facilities fully employed in their own field, but finally Fulton, on August 6, 1803, ordered an engine from them from his own drawings, intended for this purpose, repeating the order in person in 1804. It was shipped to America early in 1805, and in 1807 placed upon the Clermont, which ran upon the Hudson River as a passenger boat, attaining a speed of about five miles an hour. This was the first steamboat that was ever used for passengers, and altho Fulton neither invented the boat nor the engine, nor the combination of the two, still he is entitled to great credit for overcoming innumerable difficulties sufficient to discourage most men. Fulton, who was the son of a Scotsman from Dumfrieshire, visited Syminton's steamboat, the _Charlotte Dundas_, in Scotland, in 1801, and had seen it successfully towing canal boats upon the Forth and Clyde Canal. This was the first boat ever propelled by steam successfully for commercial purposes. It was subsequently discarded, not because it did not tow the canal boats, but because the revolving paddle-wheels caused waves that threatened to wash away the canal banks.