The screw propeller employed by Colonel Stevens in 1804 was not a new invention with him, as popularly supposed, but had its origin early in the preceding century, being a mere development of the ancient wind wheel. In 1836 it was further developed by Francis P. Smith and by Capt. John Ericsson, then living in England. Ericsson took out British patent No. 7,149, of 1836, and United States patent No. 588, of Feb. 1, 1838, and built several screw steamers, and through Capt. Robert F. Stockton, of the United States Navy, succeeded in having a screw steamer, the “Robert F. Stockton,” built in accordance with the plans of his patent and sent to the United States. The arrangement of her machinery is seen in Fig. 109. She had two propellers on the same axis, but revolving in opposite directions, one being on the central shaft and the other on a concentric tube. The engines were coupled directly to the propeller shafts, which feature was one of Ericsson’s improvements, and has continued to be the approved form to this day. In the early history of steam navigation the side wheel steamer was the favorite, and was employed for ocean travel as well as for inland waters. In 1840 the “Brittania,” the first Cunarder, commenced the career of that celebrated line. This vessel had side wheels, as did also the “United States,” shown in Fig. 110, which was the first American steamer built expressly for the Atlantic trade. In 1852 the United States mail steamer “Arctic,” of the Collins line, was regarded as the greyhound of the Atlantic, her time being 9 days, 17 hours and 12 minutes. She also had side wheels. [Illustration: FIG. 110.--STEAMER “UNITED STATES,” 1847.] Side wheel steamers for inland waters, and screw propellers for sea service, however, in time established their fitness for their respective scenes of action. In side wheel steamers the most notable improvements have been in stiffening the hull by braces, and the adoption of feathering paddle wheels, whose function is to cause the paddles to enter and leave the water in vertical position without dragging dead water. Manley in 1862, and Morgan in 1875, patented practical forms of the feathering paddle wheel. In screw propellers, Woodcroft in 1832, and Griffiths at a later period, made valuable improvements. The surface condenser was used by Hall in 1838 on the steamship “Wilberforce,” and Sickels in 1841 invented the drop cut-off. [Illustration: {“GREAT EASTERN,” SCREW AND PADDLE WHEELS, 1858. LENGTH, FIG. 111.--{692 FEET, SPEED 12 KNOTS. {“OCEANIC,” TWIN SCREW, 1899. LENGTH, 704 FEET, SPEED, 20 {KNOTS.]