Page:Collected Physical Papers.djvu/227

Rh curves similar, but of opposite sign, to those produced by light. Mechanical vibration thus produced a molecular effect opposite to that of light.

I next allowed both the stimuli to act simultaneously on one of the wires; the action of light was then found to be exactly balanced by the action of mechanical vibration, an increase or diminution of either at once upsetting the balance.

The molecular effect of mechanical vibration thus appears, at least in the case of tin, to be opposite to that produced by light. This may be the case in general; the exception might be when one of the two stimuli is normal and the other sub-minimal.