Page:Collected Physical Papers.djvu/183



Though the theory of coherence gives a simple explanation of many cases of diminution of resistance in a mass of metallic particles subjected to electric radiation, yet there are other cases which cannot be explained by that theory. If coherence be due to electric welding, it would follow that all sensitive particles would exhibit a permanent diminution of resistance; in other words, the action should be non-discriminative and there should be no self-recovery. I have shown, however, in a previous paper, that the effect of radiation is by no means non-discriminative. On the contrary, while its effect on the positive class of substances, e.g., Mg, Fe, Ni, is a diminution of resistance, its reaction on the negative class, e.g., K, Ag, Br, I, is precisely the opposite, namely an increase of resistance. Further, the conductivity change is not always permanent, since several substances are known which quickly recover and attain their original conductivity on the cessation of radiation, as if a force of restitution were called forth to restore them to their original condition.

I was thus led to suppose that the effect of radiation is to produce a state of molecular strain. Evidences will presently be adduced which will furnish proofs in support of this view.

If a substance is molecularly distorted by the action of an external agent, we may naturally expect that there would be produced changes in the physico-chemical