Page:Collected Physical Papers.djvu/203

Rh when the substance is kept immersed in a protecting medium such as naphtha, it would appear that the observed effect is primarily due to physical strain. By chemical action it is generally understood that the change is irreversible and in one direction. But in the cases of complete self-recovery exhibited by various substances, there is an automatic return to the original condition. It should, however, be borne in mind that, as a result of the strain, the chemical activity of the substance may undergo a change; a chemical action would occur if the strained substance be immersed in a medium for which it has a relatively stronger attraction.

In consequence of molecular strain produced by electric radiation a difference of potential would likely be induced between the acted and unacted portions of a substance. A voltaic cell could be made with two plates of similar substance; there would then be no P. D. between the two. But on exposing one of the two plates to the effect of radiation, a difference of potential might be established between the acted and unacted plates. The differential effect, if it exists, could then be detected by a galvanometer or an electrometer. There are, however, many difficulties in rendering this method practical. First of all, in making a voltaic combination, some kind of electrolyte is necessary, but unfortunately all electrolytes are opaque to electric radiation. This difficulty could, however, be obviated to some extent by taking an electrolyte which is almost a non-conductor (e.g., amylic alcohol) so as to be partially transparent to