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See also:FOUCAULT, See also:JEAN See also:BERNARD See also:LEON (1819—1868) , See also:French physicist, was the son of a publisher at See also:Paris, where he was See also:born on the 18th of See also:September 1819. After an See also:education received chiefly at See also:home, he studied See also:medicine, which, however, he speedily abandoned for See also:physical See also:science, the improvement of L. J. M. See also:Daguerre's photographic processes being the See also:object to which he first directed his See also:attention. During three years he was experimental assistant to See also:Alfred See also:Donne (1801—1878) in his course of lectures on microscopic See also:anatomy. With A. H. L. See also:Fizeau he carried on a See also:series of investigations on the intensity of the See also:light of the See also:sun, as compared with that of See also:carbon in the electric arc, and of See also:lime in the See also:flame of the oxyhydrogen See also:blowpipe; on the interference of See also:heat rays, and of light rays differing greatly in lengths of path; and on the See also:chromatic polarization of light. In 1849 he contributed to the Comptes Rendus a description of an electromagnetic regulator for the electric arc See also:lamp, and, in See also:conjunction with H. V. See also:Regnault, a See also:paper on See also:binocular See also:vision. By the use of a revolving See also:mirror similar to that used by See also:Sir See also:Charles See also:Wheatstone for measuring the rapidity of electric currents, he was enabled in 185o to demonstrate the greater velocity of light in See also:air than in See also:water, and to establish that the velocity of light in different See also:media is inversely as the refractive indices of the media. For his demonstration in 1851 of the diurnal See also:motion of the See also:earth by the rotation of the See also:plane of oscillation of a freely suspended, See also:long and heavy pendulum exhibited by him at the See also:Pantheon in Paris, and again in the following See also:year by means of his invention the gyroscope, he received the See also:Copley See also:medal of the Royal Society in 1855, and in the same year he was made physical assistant in the imperial See also:observatory at Paris. In September of that year he discovered that the force required for the rotation of a See also:copper disk becomes greater whenit is made to rotate with its rim between the poles of a magnet, the disk at the same See also:- TIME (0. Eng. Lima, cf. Icel. timi, Swed. timme, hour, Dan. time; from the root also seen in " tide," properly the time of between the flow and ebb of the sea, cf. O. Eng. getidan, to happen, " even-tide," &c.; it is not directly related to Lat. tempus)
- TIME, MEASUREMENT OF
- TIME, STANDARD
time becoming heated by the eddy or " Foucault currents " induced in its See also:- METAL
- METAL (through Fr. from Lat. metallum, mine, quarry, adapted from Gr. µATaXAov, in the same sense, probably connected with ,ueraAAdv, to search after, explore, µeTa, after, aAAos, other)
metal. Foucault invented in 1857 the polarizer which bears his name, and in the succeeding year devised a method of giving to the See also:speculum of reflecting telescopes the See also:form of a See also:spheroid or a paraboloid of revolution. With Wheatstone's revolving mirror he in 1862 determined the See also:absolute velocity of light to be 298,000 kilometres (about 185,000 m.) a second, or ro,000 kilom. less than that obtained by previous experimenters. He was created in that year a member of the See also:Bureau See also:des Longitudes and an officer of the See also:Legion of See also:Honour, in 1864 a See also:foreign member of the Royal Society of See also:London, and next year a member of the See also:mechanical See also:section of the See also:Institute. In 1865 appeared his papers on a modification of See also:Watt's See also:governor, upon which he had for some time been experimenting with a view to making its See also:period of revolution See also:constant, and on a new apparatus for regulating the electric light; and in the following year (See also:Comet. Rend. lxiii.) he showed how, by the deposition of a transparently thin film of See also:silver on the See also:outer See also:side of the object See also:glass of a See also:telescope, the sun could be viewed without injuring the See also:eye by excess of light. Foucault died of See also:paralysis on the 11th of See also:February 1868 at Paris. From the year 1845 he edited the scientific portion of the See also:Journal des Debts. His See also:chief scientific papers are to be found in the Comptes Rendus, 1847—1869.
See Revue See also:tours scient. vi. (1869), pp. 484-489; Prot. See also:Roy. See also:Soc. xvii. (1869), pp. lxxxiii.-lxxxiv.; Lissajous, See also:Notice historique sur la See also:vie et See also:les travaux de Leon Foucault (Paris, 1875).
End of Article: FOUCAULT, JEAN BERNARD LEON (1819—1868)
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