Page:Collected Physical Papers.djvu/224

204 I found that whereas the acted wire became cuproid with an amplitude of vibration of 4°, the same wire when vibrated through 45° became zincoid. Thus in a Pb cell (50,000 ohms in circuit):

The opposite effect under sub-minimal stimulus was too frequent to be accidental, but it did not occur invariably. On the occasions when it occurred, this negative effect disappeared after continued vibration. Thus on taking a record of effect of continued vibration, there is produced a negative twitch, which is converted later into a positive deflection, just as in the curves of effect of light (see below fig. 48).

Reversal produced by Continued Stimulation.—After the maximum effect the attainment of the further continuation of vibration tends to produce a reversal. This is specially the case with nickel in which the curve of response becomes completely reversed.

I have described the various molecular effects produced by mechanical stimulus under varying conditions, and shown how very similar they are even in details to the effects produced by electric radiation and light. How striking these similarities are will be seen from the following tabular statement and comparison of different curves.

1. The molecular effect produced may be detected either by conductivity or electromotive variation methods.