Page:Collected Physical Papers.djvu/234

214 (1) A short latent period, where there is apparently little or no action or even a transitory negative action. The curve given had to be contracted to put in all the different phases, and the peculiarities of the first part cannot therefore be very well shown.

I have previously remarked that in general the molecular strain curve is in the first part slightly convex, then straight, and in the last part concave; this is true not only under the action of stimulus of light, but also of mechanical vibration.

(2) In the second stage, the curve of response rises almost in a straight line, this being the phase of increasing action.

(3) The curve then reaches the maximum and becomes horizontal; after which it begins to fall thus exhibiting a reversal.

(4) During prolonged exposure the response-curve sometimes exhibits recurrent reversals.

The similarities of the molecular effects produced by light and by mechanical vibration have already been explained. The recurrent reversals are also occasionally obtained under mechanical vibration, as in the following