On board of some modern war-ships where speed is essential, and where the engines are driven at a very great number of revolutions per minute, as in the case of torpedo-boat catchers, the vibration throughout the whole of the vessel becomes extremely trying, not only for the nerves of the crew, but for the security of the structure itself. The cause of this vibration and consequent strain and loss of power is not far to seek. The cylinders of marine engines are always of a large diameter, 6 feet, 8 feet, or even more sometimes, and the pistons and piston-rods are necessarily of great strength and corresponding weight. Now, at every half revolution of the engines, this heavy mass of piston and piston-rod, though moving at an exceedingly high speed in the middle of the stroke, has to be brought to a standstill, and an equal velocity in the opposite direction imparted to it. A large portion of the power is therefore uselessly expended in stopping a great moving mass, and reversing its motion. All the force required to do this reacts on the vessel’s frame. Many attempts have been made to construct rotatory steam-engines, and some hundreds of patents taken out for such inventions, which in general have a piston revolving about a shaft; but the great friction, and consequent liability to wear out, have prevented their practical use. Lately, a method of using steam on the principle embodied in the water turbine has been developed, and within the last six or seven years has found successful application in propelling electro-dynamos at very high speeds. In the steam turbine there are no pistons, piston-rods, or other reciprocating parts, the effect depending on the same kind of reaction that is taken advantage of in the water turbine (which has a high efficiency in giving out a large proportion of energy), and the power is applied with smoothness and an entire absence of the oscillations that would shake to pieces any vessel that an ordinary steam-engine could propel at the same rate.