Page:Collected Physical Papers.djvu/289

Rh apparent (fig. 67). Fatigue in metal is also removed by a period of rest.

I have in this investigation mainly used the mechanical form of stimulation as being the simplest and giving rise to fewest complications. Time does not allow of my entering here upon the subject of the response under electric stimulation. I may, however, say a few words on the effect of the stimulus of light.

If one of the sensitised wires in the cell already described be subjected to light it gives an electric response, and under certain circumstances an oscillatory after-effect is seen to occur on the cessation of light. This latter fact probably explains certain phenomena of visual recurrence to be noticed presently.

The molecular strain produced by stimulus can not only be detected by the phenomena of electromotive variation, but also by conductivity variation. Acting on this principle, I have been able to construct an artificial retina constructed of galena. The sensitive receiver is placed inside a hollow spherical case, provided with a circular opening in front, in which a glass lens