Note 108 — Chapter VII

“I would here observe that a consideration of many such phenomena (the obliteration and revival of photographic drawings) has led me to regard it as not impossible that the retina itself may be photographically impressed by strong light, and that some at least of the phenomena of visual spectra and secondary colours may arise from the sensorial perception of actual changes in progress in the physical state of that organ itself subsequent to the cessation of the direct stimulant.”—On the action of the Rays of the Solar Spectrum on Vegetable Colours, &c.: by Sir J. F. W. Herschel, Bart.