464 The Theory of Aether and Electrons in the 



led to investigate* the consequences of his original hypothesis^ 

 regarding the motion of the electrons, which differs from the 

 one just described in much the same way as Grothuss' theory. of 

 electrolysis differs from Arrhenius'. Each electron was now 

 supposed to be free only for a very short time, from the moment 

 when it is liberated by the dissociation of an atom to the moment 

 when it collides with, and is absorbed by, a different atom. The 

 atoms were conceived to be paired in doublets, one pole of each 

 doublet being negatively, and the other positively, electrified. 

 Under the influence of an external electric field the doublets 

 orient themselves parallel to the electric force, and the electrons 

 which are ejected from their negative poles give rise to a current 

 predominantly in this direction. The electric conductivity of 

 the metal may thus be calculated. In order to comprise the 

 conduction of heat in his theory, Thomson assumed that the 

 kinetic energy with which an electron leaves an atom is pro- 

 portional to the absolute temperature ; so that if one part of the 

 metal is hotter than another, the temperature will be equalized 

 by the interchange of corpuscles. This theory, like the other, leads 

 to a rational explanation of the law of Wiedemann and Franz. 



The theory of electrons in metals has received support 

 from the study of another phenomenon. It was known to 

 the philosophers of the eighteenth century that the air near 

 an incandescent metal acquires the power of conducting elec- 

 tricity. "Let the end of a poker," wrote Canton,J "when 

 red-hot, be brought but for a moment within three or four 

 inches of a small electrified body, and its electrical power will 

 be almost, if not entirely, destroyed." 



The subject continued to attract attention at intervals ; 



* J. J. Thomson, The Corpuscular Theory of Matter ; London, 1907. 



f Cf. p. 457. \ Phil. Trans, lii (1762), p. 457. 



Cf. E. Becquerel, Annales de Chimie xxxix (1853), p. 355 ; Guthrie, Phil. 

 Mag. xlvi (1873), p. 254; also various memoirs by Elster and Geitel in the 

 A'nnaleri d. Phys. from 1882 onwards. The phenomenon is very noticeable, as 

 Edison showed (Engineering, December 12, 1884, p. 553), when a filament of 

 carbon is hearted to incandescence in a rarefied gas. In recent years it has been 

 found that ions are emitted when magnesia, or any of the oxides of the alkaline 

 earth metals, is heated to a dull red heal. ; , 



