Page:On the Similarities between Radiation and Mechanical Strains.djvu/11

184 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 distorting force.

7. Sub-normal stimulus often produces a reverse effect. Too long-continued disturbance produces, or tends to produce, a reversal.

8. Under peculiar moleculiarmolecular [sic] modification, the response is of opposite sign to the normal. Continued stimulation converts abnormal to normal. The response curve may thus exhibit, at the beginning, a negative twitch followed by the normal positive.

A few curves are selected from experiments already described, and given below, in order to illustrate graphically the remarkable similarities of response to different kinds of stimulus. (See fig. 15.)

They show how essentially similar are the molecular effects produced, though the modes of stimulation and the methods used for the detection of effects produced are so different.

10. Effect of Light Vibration balanced by Mechanical Vibration.

I have hitherto spoken of the similarities of the radiation and mechanical strains, but have not yet said anything about their mutual relation.

It is known that in cases where electric radiation produces an increase of conductivity, mechanical vibration produces an opposite effect, i.e., an increase of resistance. It thus appeared that we have here an exhibition of two opposite molecular effects. No definite conclusion could be drawn from this, however, as the increase of resistance may have been due to the mechanical separation of the conducting particles.

I then thought of trying the effects of light and mechanical vibration in producing electromotive variation in a strain cell. For this purpose I took a tin cell, and subjected one of the wires to the action of light and mechanical vibration alternately. The upper curve of fig. 16