These necessarily brief notices of some of the more remarkable paddle-boats of modern times, together with references in other chapters to paddle-steamers of still more recent years, are sufficient to show that the earlier form of propulsion has never been entirely superseded by the screw. Possibly the earliest definite attempt to apply the screw for propelling purposes was made by David Bushnell in his abortive submarine exploit, an account of which appears in Chapter XII. hereafter;[81] but the propeller seems to have been very primitive. The screw propeller was also proposed in 1752 by the mathematician Daniel Bernoulli. A patent was granted in 1794 to William Lyttleton for a screw propeller which was caused to revolve by an endless rope passing round a wheel at the end of the axle. It was a distinct attempt to solve the problem and nearly succeeded, but it failed because there was too much of it. Had he been contented to use one pair of blades he would have obtained better results than by using two pairs of wide blades and two odd blades, arranged with three blades on either side of the axle so that his propeller became really a long spiral wheel. He also failed from the lack of sufficient power to drive the wheel, as manual labour only was used. Still, a boat fitted with this screw was tried at the Greenwich Dock, London, and a speed of two miles an hour was stated to have been obtained. [81] See p. 376. In 1800 Mr. Shorter, master of the transport _Doncaster_, brought out two plans of propulsion. One was in the form of two duck-foot paddles with an alternate movement; the other was a two-bladed screw propeller. The latter was attached to an inclined shaft carried by a universal joint to the deck of the vessel. One of these methods was said to have moved the _Doncaster_ at a speed of about a mile and a half an hour, the contrivance being driven by eight men running round a capstan. It is difficult to believe from the picture which accompanies his plan, dated 1800, that a transport of the size depicted could have been moved at half that speed with the apparatus shown, although the fact that it was mechanically propelled is attested by credible witnesses.