Page:A history of the theories of aether and electricity. Whittacker E.T. (1910).pdf/478

 Most of the later writers on metallic conduction have preferred to take the hypothesis of Arrhenius rather than that of Grothuss as a pattern; and have therefore supposed the interstices between the molecules of the metal to be at all times swarming with electric charges in rapid motion. 11: 1898 E. Riecke effected an important advance by examining the consequences of the assumption that the average velocity of this random motion of the charges is nearly proportional to the square root of the absolute temperature. P. Drude in 1900 replaced this by the more definite assumption that the kinetic energy of each moving charge is equal to the average kinetic energy of a molecule of a perfect gas at the same temperature, and may therefore be expressed in the form, where denotes a universal constant.

In the same year J. J. Thomson remarked that it would accord with the conclusions drawn from the study of ionization in gases to suppose that the vitreous and resinous charges play different parts in the process of conduction: the resinous charges may be conceived of as carried by simple negative corpuscles or electrons, such as constitute the cathode rays: they may be supposed to move about freely in the interstices between the atoms of the metal. The vitreous charges, on the other hand, may be regarded as more or less fixed in attachment to the metallic atoms. According to this view the transport of electricity is due almost entirely to the motion of the negative charges.

An experiment which was performed at this time by Riecke lent some support to Thomson's hypothesis. A cylinder of aluminium was inserted between two cylinders of copper in a circuit, and a current was passed for such a time that the amount of copper deposited in an electrolytic arrangement