Page:Collected Physical Papers.djvu/225

Rh 2. Substances when not overstrained exhibit recovery; the recovery is, however, delayed when there is overstrain.

3. Response is modified by previous history, and the influence of the surrounding conditions. Slight rise of temperature and annealing are generally favourable to increased sensitiveness and quick recovery.

4. Under the action of electric radiation, light, and mechanical vibration, two opposite effects are exhibited; by the conductivity variation method this is seen in the diminution or increase of resistance; a positive or negative variation is obtained by the method of electromotive variation.

5. In the curve of response, in all the above cases, the ascending portion is abrupt, whereas the fall during recovery is at first rapid, then comparatively slow, the curve of recovery being thus convex to the abscissa.

6. Under rapidly succeeding stimuli, there is a fusion of individual effects; the curve rises to a maximum, when the force of restitution is kept balanced by the force of molecular distortion.

7. Sub-minimal stimulus often produces a response of opposite sign to that of normal. Too long-continued stimulation produces, or tends to produce, a reversal.

8. Under certain molecular modifications, the response is of opposite sign to that of the normal. Continued stimulation converts the abnormal into normal. The response curve may thus exhibit, at the beginning, a negative twitch followed by the normal positive.

A number of curves selected from experiments already described, are given (see fig. 46) to illustrate graphically the remarkable similarities of response under diverse modes of stimulation.