LANGLEY, SAMUEL PIERPONT

born Aug. 22, 1834, Roxbury, Mass., U.S. died Feb. 27, 1906, Aiken, S.C. American astronomer, physicist, and aeronautics pioneer who contributed to the knowledge of solar phenomena as related to meteorology and built the first heavier-than-air flying machine to achieve sustained flight. After practicing civil engineering and architecture in Chicago, Ill., and St. Louis, Mo., Langley returned to Boston, received an assistantship at the Harvard Observatory, and later taught mathematics at the U.S. Naval Academy, Annapolis, Md. In 1867 he accepted the directorship of the Allegheny Observatory and became professor of physics and astronomy at the University of Pittsburgh. His chief interest was solar activity and its effect on the weather. In 1878 he invented the bolometer, a radiant-heat detector that is sensitive to differences in temperature of one hundred-thousandth of a degree. This device enabled him to study the solar spectrum (light rays from the Sun) far into its infrared (heat-ray) region and to measure the intensity of solar radiation at various wavelengths. While at Allegheny, Langley made important experiments on the lift and drag of an aircraft moving through the air at a measured speed. Backed by these experiments, he was the first to offer a clear explanation of the way birds soar and glide without appreciable wing movement. In 1896 he became the first to build heavier-than-air machines capable of sustained (although uncontrolled) flight. Both of his unmanned crafts had two sets of 14-foot (4.3-metre) wings, weighed 26 pounds (11.8 kg), and were powered by steam engines. His first manned aircraft, powered by a five-cylinder air-cooled gasoline engine designed by Langley's assistant Charles M. Manly and piloted by Manly, snagged upon launching from a catapult, and it crashed into the Potomac River for the second and last time on Dec. 8, 1903, just nine days before the successful flights of the Wright brothers near Kitty Hawk, N.C. It had a wingspan of 48 feet (14.6 m) and a total weight (with pilot) of 850 pounds (386 kg). Some authorities believe that if his catapult had not failed, Langley would have been the first to achieve sustained flight in a manned heavier-than-air machine.