All these regard the material atom as a mere centre of force, or a hypothetical cause of sensations. Matter is therefore a manifestation of force, as to the old materialism force was a property of matter. But if matter, mind and God are nothing but sensations, then the body itself is nothing but sensations. There is no _body_ to have the sensations, and no _spirit_, either human or divine, to produce them. John Stuart Mill, in his Examination of Sir William Hamilton, 1:234-253, makes sensations the only original sources of knowledge. He defines matter as “a permanent possibility of sensation,” and mind as “a series of feelings aware of itself.” So Huxley calls matter “only a name for the unknown cause of the states of consciousness”; although he also declares: “If I am compelled to choose between the materialism of a man like Büchner and the idealism of Berkeley, I would have to agree with Berkeley.” He would hold to the priority of matter, and yet regard matter as wholly ideal. Since John Stuart Mill, of all the materialistic idealists, gives the most precise definitions of matter and of mind, we attempt to show the inadequacy of his treatment. The most complete refutation of subjective idealism is that of Sir William Hamilton, in his Metaphysics, 348-372, and Theories of Sense-perception—the reply to Brown. See condensed statement of Hamilton’s view, with estimate and criticism, in Porter, Human Intellect, 236-240, and on Idealism, 129, 132. Porter holds that original perception gives us simply affections of our own sensorium; as cause of these, we gain knowledge of extended externality. So Sir William Hamilton: “Sensation proper has no object but a subject-object.” But both Porter and Hamilton hold that through these sensations we know that which exists independently of our sensations. Hamilton’s natural realism, however, was an exaggeration of the truth. Bowne, Introd. to Psych. Theory, 257, 258—“In Sir William Hamilton’s desire to have no go-betweens in perception, he was forced to maintain that every sensation is felt where it seems to be, and hence that the mind fills out the entire body. Likewise he had to affirm that the object in vision is not the thing, but the rays of light, and even the object itself had, at last, to be brought into consciousness. Thus he reached the absurdity that the true object in perception is something of which we are totally unconscious.” Surely we cannot be immediately conscious of what is outside of consciousness. James, Psychology, 1:11—“The terminal organs are telephones, and brain-cells are the receivers at which the mind listens.” Berkeley’s view is to be found in his Principles of Human Knowledge, § 18 _sq._ See also Presb. Rev., Apl. 1885:301-315; Journ. Spec. Philos., 1884:246-260, 383-399; Tulloch, Mod.