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In the section of his Farbenlehre dealing with 'physiological colours', Goethe devotes by far the most space to the so-called 'afterimages' which appear in the eye as the result of stimulation by external light, and persist for some little time. To create such an afterimage in a simple way, one need only gaze at a brightly lit window and then at a faintly lit wall of the room.
The routine explanation of the appearance of movement was accordingly: that every picture of a particular position left in the eye an afterimage until the next picture with the slightly changed position of the jumping animal or of the marching men was in sight, and the afterimage of this again lasted until the third came.
We speak of this effect as a positive afterimage, because it is a real continuation of the first impression and stands in contrast to the so-called negative afterimage in which the aftereffect is opposite to the original stimulus. In the case of a negative afterimage the light impression leaves a dark spot, the dark impression gives a light afterimage.
If at dark we twirl a glowing joss stick in a circle, we do not see one point moving from place to place, but we see a continuous circular line. It is nowhere broken because, if the movement is quick, the positive afterimage of the light in its first position is still effective in our eye when the glowing point has passed through the whole circle and has reached the first position again.
Black becomes white and white becomes black; in the world of colors red leaves a green and green a red afterimage, yellow a blue and blue a yellow afterimage. If we look at the crimson sinking sun and then at a white wall, we do not see red light spots but green dark spots.
Headlights flashed an angry light at the severed trailer, the pretzel-shaped wheel, and the fallen gear strewn in disarray. Then the lights were gone, leaving behind a fiery-comet afterimage. I wondered why Atmananda had fed me the drug. Did he actually believe that he was helping me? If so, why didn't he recommend that I seek guidance outside his direct sphere of influence?
It is not necessary to go further into details in order to demonstrate that the apparent movement is in no way the mere result of an afterimage and that the impression of motion is surely more than the mere perception of successive phases of movement. The movement is in these cases not really seen from without, but is superadded, by the action of the mind, to motionless pictures.
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