born Aug. 22, 1834, Roxbury, Mass., U.S.
died Feb. 27, 1906, Aiken, S.C.
U.S. astronomer and aeronautics pioneer.
He taught for many years at the future University of Pittsburgh. He studied the effect of solar activity on weather and invented the bolometer (1878), a radiant-heat detector sensitive to extremely small temperature differences. He began conducting experiments on lift and drag of wings by building flying machines, and in 1896 one of his heavier-than-air machines became the first to achieve sustained unmanned flight, flying 3,000 ft (900 m) along the Potomac River.