Langley, Samuel (Pierpoint)(1834–1906) inventor, aeronautical pioneer; born in Roxbury, Mass. Although he had no formal higher education, he served for twenty years as director of the Allegheny Observatory (1867–87). While director, he created a system of regulating railroad time that became standard. In 1878 he invented a bolometer, an electrical thermometer, which he used to conduct experiments on solar and lunar radiation. From 1887 to 1906 he served as secretary of the Smithsonian Institution. He built several models of heavier-than-air mechanically propelled flying machines, and in 1896 he achieved the first free flights. His subsequent attempt to build and fly a man-carrying machine failed.
Born Aug. 22, 1834, in Roxbury, Mass.; died Feb. 27, 1906, in Aiken, S.C. American astrophysicist.
Langley was appointed director of the Allegheny Observatory in 1867. Beginning in 1887 he was at the Smithsonian Institution in Washington. Langley studied the distribution of energy in the solar spectrum and reestablished the solar constant. He invented the bolometer in 1880–81 and used it to measure the intensity of solar radiation. On the basis of these measurements, Langley compiled an atlas in 1901 of the infrared part of the solar spectrum.