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spontaneous conviction of the existence and nature of external objects involves many judgments besides this one of causation. I see the apple before me. My present impression is the steps of my past experience being unanalyzed that I see it to be round, to be red, to be three inches in diameter and at a distance of three feet. How does this impression agree with what Sir William Hamilton says is the real object of perception? " Through the eye we perceive nothing but the rays of light in relation to, and in contact with the retina." "Who ever perceived them, or came to so much as a knowledge of them, without diligent scientific inquiry? Light, as the fruit of much research, is found to be a form of motion, and this motion to affect the retina; but no man ever knows the existence of the retina, or of the undulations of light thereon, save through an inquiry into eyes other than his own, and a careful investigation of the physical world. What is here asserted to be the sole object of perception, the mind never perceives, but only employs it as a submerged, unknown cause through which it arrives at its own knowledge, to wit: a red apple of a given size and position. In this final product of perception, there are contained innumerable judgments, and it should certainly be no surprise to find among them this one of outside existence. That the spaces of the world are inferentially given, is entirely in keeping with the fact that those of a painting are, by the previous habit and impulse of the mind, supplied under suitable suggestions of light and shade.

The crude material granted to the mind seems to be a subjective impression of redness, of angular extension and various shades. From these, by the aid of muscular and tactual experience, and the help afforded by the color and relations of surrounding objects, it constructs an apple and assigns it independent existence in a definite locality. This