conditions proposed of advancing the boat faster, the more rapid the stream; and when at anchor such wheels might have been applied to the other purposes.” Floating mills, worked by large water-wheels, may be seen on the Rhine to-day. Papin, the French philosopher, while in England, witnessed an experiment on the Thames, in which a boat, fitted with revolving oars or paddles, was worked from a kind of treadmill turned round by horses. “The velocity with which this horse-boat was impelled was so great, that it left the king’s barge, manned with sixteen rowers, far astern in the race of trial.” In 1682, a horse tow vessel was used at Chatham. It was “constructed with a wheel on each side of the vessel, connected by an axle going across the boat, and the paddles were made to revolve by horses moving a wheel turned by a trundle fixed on the axle. It drew but four and a half feet of water, and towed the greatest ships by the help of four, six, or eight horses.” In 1729, Dr. John Allen obtained a patent for his new invention, one which has been revived with some success in later days. It was to propel a vessel by forcing water through the stern, at a convenient distance under the surface of the water, into the sea, by suitable engines on board. “Amongst,” says the doctor, “the several and various engines I have invented for this purpose, is one of a very extraordinary nature, whose operation is owing to the explosion of _gunpowder_, I having found out a method of firing gunpowder in vacuo, or in a confined space, whereby I can apply the whole force of it, which is inconceivably great, so as to communicate motion to a great variety of engines, which may also be applied in working mines and other purposes.” And again, in 1760, a Swiss clergyman published a pamphlet in London, in which oars worked with springs were to be used, and the expansive power of gunpowder was to be used to bend the springs. He states, candidly enough, that since he arrived in England he had learned that thirty years before a Scotchman had proposed to make a ship proceed by means of gunpowder, but that thirty barrels had scarcely forwarded it ten miles. We may smile at these attempted uses of gunpowder, but they were doubtless suggested by the scientific studies of the day, which were particularly directed to the expansive power of vaporised water. In our own day, steam has been substituted for powder in discharging a cannon. Perkins’ “steam-gun” was long one of the curiosities of the Polytechnic Institution.