your first thought probably is that the line should be carried on in the same direction—should be produced; but you see at once (the moment it is pointed out to you) that such a movement is not a movement of the line, but is still merely a movement of the point. You cannot move the line, then, by continuing it at one or at both ends. To move the line you must move it laterally. That alone is the movement of the line. The lengthening of the line is, as I said, merely the movement of the point. The movement of the line then generates a surface. Now, move the surface. Here, too, you must be on your guard against continuing your lateral motion, for that is merely a continuation of the motion of the line; and this is not what is required. You are required to move not the line, but the surface; you must therefore move the surface either up or down into the third dimension of space, namely, depth; and these three movements give you the scheme of solid. You have merely to suppose this scheme filled with visible and palpable matter, that is, with something which is an object for the particular faculty in man, to obtain a solid atom; and out of atoms you can construct the universe at your discretion.
19. It seems at first sight a marvellous piece of foolishness that a philosopher should ascribe to empty unsubstantial number a higher degree of reality than he allows to the bright and solid objects which constitute the universe of matter. The ap-
