In 1836 Captain John Ericsson, a Swede, then residing in London, and Mr. T. P. Smith, of the same place, almost simultaneously had each small boats built for the purpose of testing the screw. Ericsson’s boat, named the _Francis B. Ogden_, was 45 feet long and 8 feet beam, and was fitted with two screw-propellers attached to the same shaft. The first experiment made on the Thames was successful beyond all expectation, for he towed the Admiralty barge, with a number of their Lordships on board, from Somerset House to Blackwall and back, at the rate of ten miles an hour. Smith’s boat was equally successful, the immediate result being the formation of a joint stock company, called the Screwship Propeller Company, who bought out Mr. Smith’s patent and proceeded to build the _Archimedes_, a vessel of 237 tons, and 80 horse-power. Smith’s original propeller was a genuine screw, with two whole turns of the thread, made to revolve rapidly under water in the dead-wood of the vessel’s run. In the meantime, about 1838, Mr. James Lowe obtained a patent for an important modification of the elongated screw-propeller. This consisted in making use of curved blades, each a portion of a curve, which, if continued, would form a complete screw. The “pitch of the screw ” being the whole length along the spindle shaft of one complete turn of the screw, if fully developed, it was found that by reducing the pitch to a segment of the screw and increasing the diameter, the propeller could be reduced to more convenient dimensions. The success of the _Archimedes_ at length induced the Admiralty to make trial of the screw in the Royal Navy. The first _Rattler_ was built in 1841, and fitted with a screw-propeller. In 1842 the United States Government made a similar experiment with the _Princeton_, and in the following year the French Government built the screw war-ship, _Pomone_.[12] In each case the verdict was favourable to the introduction of the screw in preference to the paddle-wheel. The second _Rattler_, of 880 tons and 496 horse-power, was built and fitted with a screw-propeller, and attained a speed of 9¼ knots on her trial trip, September 5th, 1851. That settled the question in so far as the Royal Navy was concerned. In the mercantile marine the _Great Britain_ was the first ship of large dimensions in which the screw was adopted. For many years there continued to be a strong prejudice against it, though it was destined eventually to entirely supersede the paddle on the ocean. In order to prevent the screw “racing,” which often occurs in heavy weather, to the discomfort of passengers and the annoyance of engineers, a system of raising and lowering the propeller has been tried somewhat extensively in the navy and also in the mercantile service, but it has been practically abandoned since the twin screws have come into general use, by which the difficulty alluded to has been largely overcome. [Illustration: A MYTHICAL WIND-BOAT, FROM AN OLD ENGRAVING (1805).]