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LANGLEY, SAMUEL PIERPONT (1834-1906)
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See also:LANGLEY, See also:SAMUEL PIERPONT (1834-1906) , See also:American physicist and astronomer, was See also:born at See also:Roxbury, See also:Boston, See also:Massachusetts, on the 22nd of See also:August 1834. After acting for a See also:short See also:time as assistant in Harvard See also:College See also:Observatory, he was appointed assistant See also:professor of See also:mathematics in the U.S. See also:Naval See also:Academy in 1866, and in the following See also:year became director of the See also:Allegheny Observatory at See also:Pittsburg, a position which he held until his selection in 1887 as secretary of the Smithsonian Institution at See also:Washington. His name is especially associated with two See also:main branches of investigation—See also:aeronautics, and the exploration of the infra-red portions of the See also:solar spectrum. The study of the latter he took up as a result of the publication in 1871 of an See also:energy-See also:curve of the spectrum by S. I. Lamansky. The imperfections of the thermopile, with which he began his See also:work, led him, about 188o, to the invention of the bolometer, an See also:instrument of extraordinary delicacy, which in its most refined See also:form is believed to be capable of detecting a See also:change of temperature amounting to less than one-See also:hundred-millionth of a degree Centigrade. Depending on the fact that the See also:electrical conductivity of a metallic conductor is decreased by See also:heat, it consists of two strips of See also:platinum, arranged to form the two arms of a See also:Wheatstone See also:bridge; one See also:strip being exposed to a source of See also:radiation from which the other is shielded, the heat causes a change in the resistance of one See also:arm, the See also:balance of the bridge is destroyed, and a deflection is marked on the See also:galvanometer. The platinum strips are exceedingly See also:minute, being in some cases only i o in. in width, and less than one-tenth of that amount in thickness. By the aid of this instrument, Langley, working on See also:Mount See also:Whitney, 12,000 ft. above See also:sea-level, discovered in 1881 an entirely unsuspected See also:extension of the invisible infra-red rays, which he called the " new spectrum." The importance of his achievement may be judged from the fact that, while the visible spectrum includes rays having See also:wave-lengths of from about 0•4 to o•76 µ, and no invisible heat-rays were known before 1881 having a wave-length greater than 1.8 he detected rays having a wave-length of 5•3 µ. In addition, taking See also:advantage of the accuracy with which the bolometer can determine the position of a source of heat by which it is affected, he mapped out in this infra-red spectrum over 700 dark lines or bands resembling the See also:Fraunhofer lines of the visible spectrum, with a probable accuracy equal to that of refined astronomical observations. In aeronautics he succeeded in demonstrating the practicability of See also:mechanical See also:flight. He first undertook a preliminary inquiry into the principles upon which flight depends, and established at Allegheny a huge " whirling table," the revolving arm of which could be driven by a See also:steam-See also:engine at any circumferential See also:speed up to 70 M. an See also:hour. The construction of a flying See also:machine was next attempted. The first difficulty was to make it sufficiently See also:light in relation to the See also:power its machinery could develop; and several See also:machines were built in which trials were made of steam, and of compressed 4air and carbonic See also:acid See also:gas as See also:motive agents. About 1893 a, satisfactory machine was ready, and a new See also:series of troubles had to be faced, for it had to be launched at a certain initial speed, and in the See also:face of any See also:wind that might be blowing. To enable these conditions to be fulfilled, as well as to ensure that the machine, when it See also:fell, should fall on See also:water, the experiments were carried out on the See also:Potomac See also:river, some 30 M. below Washing-ton. It was not till the autumn of 1894 that an efficient launching apparatus was devised, and then the wings were found not to be strong enough to See also:bear the pressures to which they were subjected. Various other delays and mishaps followed, but ultimately, on the 6th of May 1896, a successful flight was made. On that See also:day an aerodrome, weighing about 30 lb and about 16 ft. in length, with wings measuring between 12 and 13 ft. from tip to tip, twice sustained itself in the See also:air for 11 minutes (the full time for which it was supplied with See also:fuel and water), and traversed on each occasion a distance of over See also:half a mile, falling gently into the water when the engines stopped. Later in the same year, on the 28th of See also:November, a similar aerodrome flew about three-quarters of a mile, attaining a speed of 30 M. an hour. In 1903 he experimented with an aerodrome capable of carrying a See also:man, but repeated accidents prevented it from being launched, and finally through lack of funds the experiments had to be abandoned without the machine ever having been See also:free in the air (see a:so FLIGHT AND FLYING). Langley died on the 27th of See also:February 1906. Additional information and CommentsThere are no comments yet for this article.
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