Page:Collected Physical Papers.djvu/243

 XVII

ON THE CHANGE OF CONDUCTIVITY OF METALLIC PARTICLES UNDER CYCLIC ELECTROMOTIVE VARIATION

A mass of conducting particles has its conductivity changed when subjected to rapid electric vibration, as for instance, when acted on by electric waves. I have, in previous papers, adduced reasons leading to the conclusion that electric radiation produces a molecular change, and that conductivity variation is the expression of the induced change. We know that the physical properties of a given substance depend on its molecular condition. Any molecular change that may be induced may therefore be expected to be attended by changes in the physical properties of the substance, electric conductivity being one of these. The wide difference in electric conductivity of the same substance under different molecular conditions is seen in the case of carbon, in its two allotropic forms of graphite and diamond. The effectiveness of radiation in producing allotropic changes is seen in the conversion of the yellow into the red variety of phosphorus under the action of light.

That the variation of conductivity induced by electric radiation is due to some atomic or molecular action is seen from the fact that it is dependent on the chemical nature and the molecular condition of the substance. Thus, under electric radiation, the positive class of substances, e.g., Fe, Mg, etc., exhibit an increase of conductivity, whereas the negative class of (223)