led to investigate[1] the consequences of his original hypothesis[2] 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 proportional 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 electricity. "Let the end of a poker," wrote Canton,[3] "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[4];
- ↑ J.J. Thomson, The Corpuscular Theory of Matter; London, 1907.
- ↑ Cf. p. 457.
- ↑ Phil. Trans. lii (1762), p. 457.
- ↑ Cf. E. Becquerel, Annules de Chimie xxxix (1853), p. 355; Guthrie, Phil. Mag. xlvi (1873), p. 264; also various memoirs by Elster and Geitel in the Annalen 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 heated 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 heat.
