an uncircumscribed and modifying principle, but as circumscribed and modified; that we have to do with a luminous image; with images or circumscribed objects generally, whether light or dark: this was the purpose we had in view, and such is the problem to be solved.
362.
All that takes place in dioptrical cases,—especially those of the second class which are connected with the phenomena of refraction,—is now sufficiently familiar to us, and will serve as an introduction to what follows.
363.
Catoptrical appearances remind us of the physiological phenomena, but as we ascribe a more objective character to the former, we thought ourselves justified in classing them with the physical examples. It is of importance, however, to remember that here again it is not light, in an abstract sense,