3. On the Physiological Action of Light. No. II.

Extract

Since the date of the first communication, we have endeavoured to obtain quantitative results involving time as a variable element in the case of the action of light on the retina and optic nerve, We have therefore found it necessary to construct a true graphical representation of the variations of the electro-motive force occasioned by the impact and cessation of light. It is clear that to register minute galvanometrical alterations, the only plan that could be employed would be to photograph on a sensitive surface, covering a cylinder rapidly revolving on a horizontal axis, the alteration of position of the spot of light reflected from the mirror, just as continuous magnetic observations are registered.