We will proceed in due order to consider and examine these elements of the visible world, as well as the relation in which the organ itself stands to them, and for this purpose we take the simplest objects.
[1] The German distinction between subject and object is so generally understood and adopted, that it is hardly necessary to explain that the subject is the individual, in this case the beholder; the object, all that is without him.—T.
[II.]
EFFECTS OF BLACK AND WHITE OBJECTS ON THE EYE.
In the same manner as the retina generally is affected by brightness and darkness, so it is affected by single bright or dark objects. If light and dark produce different results on the whole retina, so black and white objects seen at the same time produce the same states together which light and dark occasioned in succession.
A dark object appears smaller than a bright one of the same size. Let a white disk be placed on a black ground, and a black disk on a white ground, both being exactly similar in size; let them be seen together at some distance, and we shall pronounce the last to be about a fifth part smaller than the other. If the black circle be made larger by so much, they will appear equal.[1]