Page:Collected Physical Papers.djvu/313

Rh in A and B wires to a succession of uniform stimuli. Hot water was now substituted for the cold water (too high a temperature temporarily reduces the response); the cell was then allowed to cool to its old temperature. Records show how the process of annealing had greatly enhanced the amplitude of response.

Effect of Previous Vibration.—The increased sensitiveness conferred by previous vibration has already been referred to before. I give below a record (fig. 77) obtained with platinum; this and similar results obtained

with other metals clearly show the enhancement of response after preliminary stimulation.

Sometimes the wire gets into a very sluggish condition, when the response almost disappears; in other words, owing to some molecular modification, responsiveness is reduced from the normal positive value (by positive is meant that the acted wire becomes zinc-like or is zincoid) to zero. In these cases annealing or preliminary vibration are usually effective in transforming the sensitiveness from zero to the normal positive value.