of his paddle-boat on the Thames. Returning to Marburg, of which university he was professor, he thought over what he had seen, and it occurred to him to combine the two contrivances in one, and to apply Savery's motive power in the pump to drive Savery's paddle-wheels. But it took him fifteen years to fit up a boat that worked to his satisfaction. "It is important," he wrote to Liebnitz on 7 July, 1707, "that my new construction of vessel should be put to the proof in a seaport like London, where there is depth enough to apply the new invention, which, by means of fire, will render one or two men capable of producing more effect than some hundreds of rowers." Papin's boat that he intended to send to London was destroyed by some watermen, who feared the new invention might interfere with their trade.
Savery proposed to apply his engine to various purposes. One was to pump water into a reservoir for the production of an artificial waterfall for driving mills or any other ordinary machinery; that is to say, by means of steam he would lift a body of water which by flowing back might drive an overshot wheel, from the rotation of which the motive power for any other mechanical operations would be derived. This, however, was never done, and Savery's engine continued to be employed only in the drainage of Cornish mines. But it had this disadvantage, that it could not heave water but to about eighty feet, and as the depth of mines was from fifty to a hundred yards, the only way to exhaust the water was by erecting several engines in successive stages, one above the other. But the expense of fuel and attendants and the constant danger of explosions rendered it clear that the use of his engine for deep mines was altogether impracticable. Such was the state of affairs when Thomas Newcomen,
