If you multiply two feet by two feet, the result represents a plain surface, or figure of two dimensions. If you multiply two feet by two feet by two feet, you have a solid, or figure of three dimensions--such as the world in which we live and move. But now, suppose you multiply two feet by two feet by two feet by two feet, what does that represent? For ages the minds of mathematicians and philosophers have been tempted by this fascinating problem of the "fourth dimension." They have worked out by analogy what such a world would be like. If you went into this "fourth dimension," you could turn yourself inside out, and come back to our present world in that condition, and no one of your three-dimension friends would be able to imagine how you had managed it, or to put you back again the way you belonged. And in this, it seems to me, we have the perfect analogy of metaphysical thinking. It is the "fourth dimension" of the mind, and plays as much havoc with sound thinking as a physical "fourth dimension" would play with--say, the prison system. A man who takes up an absolute--God, immortality, the origin of being, a first cause, free will, absolute right or wrong, infinite time or space, final truth, original substance, the "thing in itself"--that man disappears into a fourth dimension, and turns himself inside out or upside down or hindside foremost, and comes back and exhibits himself in triumph; then, when he is ready, he effects another disappearance, and another change, and is back on earth an ordinary human being. The world is full of schools of thought, theologians and metaphysicians and professors of academic philosophy, transcendentalists and theosophists and Christian Scientists, who perform such mental monkey-shines continuously before our eyes. They prove what they please, and the fact that no two of them prove the same thing makes clear to us in the end that none of them has proved anything. The Christian Scientist asserts that there is no such thing as matter, but that pain is merely a delusion of mortal mind; he continues serene in this faith until he runs into an automobile and sustains a compound fracture of the femur--whereupon he does exactly what any of the rest of us do, goes to a competent surgeon and has the bone set. On the other hand, some devoted young Socialists of my acquaintance have read Haeckel and Dietzgen, and adopted the dogma that matter is the first cause, and that all things have grown out of it and return to it; they have seen that the brain decays after death, they declare that the soul is a function of the brain--and because of such theories they deliberately reject the most powerful modes of appeal whereby men can be swayed to faith in human solidarity.