LANGLEY, SAMUEL PIERPONT Ameri can physicist and astronomer who first demonstrated the prac ticability of mechanical flight (May 6, 1896), was born at Rox bury, Mass., Aug. 22, 1834. He was educated in the Boston Latin School and in Europe. After a few years of practising architecture and civil engineering and holding assistant professorships in Har vard College Observatory and the U.S. Naval Academy, he be came director of the Allegheny Observatory and professor of physics and astronomy in what was then known as the Western university of Pennsylvania (1867). He held this position until his election in 1887 as secretary of the Smithsonian Institution at Washington.
Langley's name became especially associated with two main branches of investigation—aeronautics and the exploration of the infra-red portions of the solar spectrum. When he took up the study of the distribution of energy in the solar spectrum he found the most delicate existing instrument, the thermopile, far too sluggish for his needs and invented the bolometer, which depends on the fact that the electrical conductivity of a metallic conductor is decreased by heat. This instrument has no superior to-day. In its most refined form it is believed to be capable of detecting a change of temperature amounting to less than one-hundred millionth of a degree. By its aid Prof. Langley pushed his investi gations of the solar spectrum into previously unexplored regions in the infra-red radiations, discovering unsuspected extensions of the invisible infra-red rays which he called the "new spectrum." He began his work in aeronautics by a preliminary inquiry into the principles upon which flight depends, as he doubted the sound ness of the prevailing theories as to how birds fly. After he had satisfied himself, by experiment with a huge "whirling table," that "it was possible to construct machines that would give such velocity to inclined surfaces that bodies definitely heavier than air could be sustained upon it and moved through it with great velocity," and after studying the irregularities of the winds, he began the construction of several model flying-machines.
He succeeded (May 6, 1896) in launching his "aerodrome," weighing 26 lb. and about 16 ft. in length, with wings measuring
between 12 and r3 ft. from tip to tip. It twice sustained itself in the air for about 1 minutes (the full time for which it was supplied with fuel and water) and traversed on each occasion a distance of over half a mile, falling gently into the water of the Potomac over which it had been launched, when the engines stopped. Later in the same year (Nov. 28) a similar aerodrome New about three-quarters of a mile, attaining a speed of 3o m. an hour. Never in the history of the world, previous to these at tempts, had any such mechanism, however actuated, sustained it self in the air for more than a few seconds. He thus paved the way for others who have achieved success with man-carrying machines.
Although Langley announced soon after these experiments that he had brought to a close the portion of the work which seemed to be especially his, "the demonstration of the practicability of mechanical flight," he experimented, in 1903, with the aerodrome capable of carrying a man. This attempt was accompanied by re peated failures and a chorus of ridicule and attack from an un sympathetic press, so that the further Government financial sup port which was necessary was not given. This was a severe blow to Langley, then 7o years old, but he never wavered in his con fidence that ultimately success would be certain to result from his work, and it is true that the principles which he discovered have gained steadily in importance. Years later a test of his man-carrying machine made at the Curtiss shops demon strated its inherent stability and remarkable ease of control.
Langley died on Feb. 27, 1906. His published works, covering a wide range of topics, include nearly 200 titles.
A complete bibliography of his work may be found in the Biog. Memoirs of the Nat. Acad. of Sciences, vol. vii. See this source for complete biography. Also Aircraft, vol. vii., pp. 5-6 (New York, 1916) ; Proceedings of the Royal Society of Edinburgh, vol. 26, pp. (1907) ; C. P. Adler in Bulletin of the Philosophical Society of Wash ington, vol. 15, pp. 1-26 ; Henry Feffman "A Tribute to Samuel P. Langley," Annual Report of the Smithsonian Institution, 1917-18, pp. 157-167.