The third classes of devices above mentioned assume atmospheric pressure, and a piston driven by atmospheric pressure. This is easily attained, but in order for atmospheric pressure to drive a piston it must only be on one side of the piston, and when the piston has been driven what force and energy will be required to put it in a position again such that there will be atmosphere on only one side, and a vacuum into which it can retire, on the other side? It is easily answered. The same work must be done, and the same work exactly, to put the piston again in the position with the vacuum with equal dimensions into which it can be driven by atmospheric pressure, that first drove it to occupy the vacuum--exactly the same work, and no less and no more, except that the amount lost by friction must be supplied in addition. CHAPTER V MAGNETIC DEVICES A Magnetic Pendulum Here we present a device for Perpetual Motion by magnetism, but we are unable to give the inventor's name or his nativity. It seems to have been brought forth in the early part of the nineteenth century, prior to 1828. The description is as follows: Let A A, in the prefixed engraving, represent two magnets revolving on axes. Let B represent a larger magnet, hanging on an axis, pendulum fashion, between the two former. As the poles of the two smaller magnets lie in the same direction, the effect will be to draw the larger magnet towards that on the left hand, while it is at the same time repelled by that on the right; but while this is going on, the upper end of the large magnet raises by means of a guide wire, the tumbler D, which, just before the magnets come in contact, passes the perpendicular and falls over, carrying with it the lever connected with the two wheels C C, and causing them to perform a quarter revolution; these wheels are connected by lines with two small wheels fixed on the axles of the two magnets A A. While the former make a quarter revolution, the latter turn half round; consequently, the position of the magnets is reversed, and the same motions are then performed by the pendulum magnet being attracted and repelled in the opposite direction; and just before the magnets touch each other the arrangement is again instantly reversed. [Illustration] Magnetic-Driven Wheel Another plan for Perpetual Motion by magnetism appeared in the public journals of England in 1828. The inventor states in effect that he desires to get before the readers an "Attempt at Perpetual Motion by Means of Magnetism, Applied in a New Way." His attempt as published is as follows: The object of the present communication is to lay before your readers an attempt at perpetual motion by means of magnetism applied somewhat differently to any that has yet been published in your Magazine. [Illustration]