of ethereal wave-lengths? Not at all. That may be presupposed, but it will not do the work by itself. Blue is a peculiar "effect"; effect, I mean, in the artistic sense of the word; and wave-lengths, received say on a photographic plate, are not the peculiar effect which we call blue, even if as a physical cause they were to produce it qua physical effect. How do the elements of the effect hold together? What makes the blue reinforce or modify the blue? There is no push or pull between them. They work on each other through their identity and difference; or, to avoid disputes, here irrelevant, through their likeness and unlikeness. What sort of medium does such a unity involve? Surely, that of consciousness and no other. Blue, then, while it retains the characters of blue, must have in it the life of mind. I do not call it "mental," for I am not sure what that means. But I will call it logical. This argument, I am convinced, might be much better stated, but it at least makes an attempt to express a central consideration which I have uneasily
