In the first place, let us describe the machine. Fig. 1: A is a sectional view of the interior of the wheel, which is formed in two halves upon one shaft; each half or section is furnished with a projecting ledge and an opening is left between the two ledges sufficiently wide to admit of a magnet being introduced between them, by which arrangement the magnet may be brought as near to the ball as may be necessary (see Fig. 2). B is a magnet whose line of attraction acts at right angles with the line of gravity. C is an iron ball under the action of two forces. The magnet continually drawing the ball up the inclined plane within the wheel, and gravity continually drawing it to the bottom, by their united action it was supposed the wheel would revolve forever, or till it was worn out; upon the same principle that a wheel revolves by the animal force or muscular action of a mouse or squirrel, which carries it up the inclined plane, whilst it is continually drawn to the bottom by the action of gravity, thereby causing the wheel to revolve by the weight of its body. The model was taken from the earth's motion round the sun; and the following process of reasoning seemed to justify the assumption that the wheel would move on till it was worn out: "The earth is carried round the sun by the action of two forces, one of which is momentum, which is not, in reality, a force or cause of motion, but an effect derived from an original impulse; and that impulse or the momentum derived from it is not destroyed, because there is no resistance to the moving body--that is, there is no friction. Well, I cannot make this machine without having resistance to the motion--that is, friction; but to compensate for this I have two real forces, two causes of motion, each of them capable of imparting momentum to a body: they are both constant forces; and from one of them, the magnet, I can obtain any power that may be required within certain limits." [Illustration] This reasoning appeared conclusive, and the wheel was made; but when the magnet was applied instead of the ball rolling up the inclined plane, the wheel moved backwards upon its center. It occurred to me that by placing a small ratchet upon the wheel, as shown at D, this backward motion of the wheel on its center might be prevented, in which case the ball must roll up the inclined plane, and that a perpetual motion might then ensue; but this ratchet I never tried, having about that time begun to perceive that the idea of a perpetual mechanical motion, either on the earth or in the heavens, involves an absurdity; and that, therefore, the motions of the planets must necessarily carry them continually nearer and nearer to the center of attraction. The above described device by Mr. Mackintosh brought forth the following comment from R. Munro, which was published in 1836: