The above is a wheel of light construction, moving on friction wheels _in vacuo_; the rim is furnished with slips of steel--pieces of watch-spring will do. N N are two magnets, which, attracting the rim of the wheel, will render one side lighter and the other heavier, causing it to revolve _ad infinitum_: or to render it more powerful, let the steel rims be magnetized and fixed on the wheel with their north poles towards its center. Let two more magnets be added, as shown by the dotted lines: let these two, S S, be placed with their south poles nearest the rim of the wheel; and the other two, N N, with their north poles in that position. Now, as similar poles repel and opposite poles attract, the wheel will be driven round by attraction and repulsion acting conjointly on four points of its circumference. B B are blocks of wood to keep off the attraction of the magnets from that part of the wheel which has passed them. Mackintosh's Experiment F. S. Mackintosh, of England, in 1823, sought to accomplish Perpetual Motion, and made the attempt here described. It was not made public until 1836, when it was published in "Mechanics' Magazine." In the meantime, the inventor had become convinced of the impossibility of perpetual motion, as his comments on his own alleged invention discloses. (The classification in this book of Mackintosh's invention is somewhat doubtful. The article as contributed in 1836 would as aptly be classified under arguments against Perpetual Motion, Chapter XII. But, in view of the fact that at the time of the invention the inventor was seriously working at a scheme for the accomplishment of Perpetual Motion, it has been decided to classify it under Magnetic Perpetual Motion Devices.) The published article was in the nature of a contribution from the inventor, and is as follows: I herewith forward you a description of a machine which was constructed by me in the year 1823, with a view to produce a perpetual motion. With this machine and the studies necessarily connected with it, first originated the suspicion that the planets could not continue in motion unless they gradually approached the center of the attraction.