The physiologist will step in and speak to you of the structure of the eye--the susceptibility of its retina for special impressions; there he says you may find colour. Put both accounts together, and they appear as part-causes, each a factor helping to make up a result; which result physicist and physiologist would agree to call colour. Yet again: Suppose the human and animal world were deprived of all consciousness, all which in the widest meaning we call mind--their eyes remaining like mirrors, telescopes, microscopes; perfect instruments, only every kind of intelligence, instinctive or rational, gone. Where would colour then be? The sun might play upon cloud or rain, the light of a rainbow be reflected in the eye. Were there but perceiving mind, the impression would exist. But we are supposing the impressible to be wanting; there is no sensation, no percipient; colour must remain unknown, for there is nothing capable of observing it. Now this shows you, first, how important it is to emphasize the word _observed_ added to phenomenon. It shows you, secondly, _where_ the ultimate seat of every observation really lies; each observed phenomenon, each positive fact, is at last neither more nor less than a mental state. The evidence for each fact is the condition of your own mind, your consciousness as it is called. You may sift the thing witnessed, verify, examine, and cross-examine; but after all, your own consciousness is the first real evidence you have got. It would seem, then, that the most positive of all sciences would be the science of mind; and the next most positive the sciences which enable us to draw conclusions from our positively existing mental states; the statements, we may call them, which our minds make to us. Yet, strange to say, the very first thing Positivism does is to dispense with a science of mind, as mind, altogether. Mr. Mill makes it a severe reproach against Comte, that he ignores both psychology and logic; recognizes no power in the mind, even of self-observation; accepts no theory even of the inductive process. Mr. Mill characterises Comte's want of mental science as "a grave aberration."[12] It is indeed so. This appears plainly enough in the example just adduced from our commonest sensation, the every-day phenomenon of colour. It was made up, you saw, of three factors, a physical antecedent, a condition of the sensitive apparatus, and a mind which received into its consciousness the impression instrumentally conveyed to it. This last, you will remember, was the _first_ fact to us. It is _the_ fact: the revelation of an outward world, its changes and its continuing presence, its rest and its constant motion. Without this fact of inward consciousness, nature would have possessed no more significance than pictures seen in the eyes of the newly dead.