The result of Mr. Mackintosh's essay at perpetual motion might be attributed to the avoidable friction caused by the manner in which the iron ball is placed in the wheel. Curious to try the experiment, I proceeded, and, with the view of diminishing the friction, I placed two wheels on the axis of the ball, but the result was precisely that described by Mr. Mackintosh. I next applied the ratchet, as suggested, but with no better effect; the ball rolled towards the magnet, but did not give the required motion to the wheel. It is not unlikely, then, that the present ingenious attempt will not be realized. Spence's Device John Spence, of Linlithgow, Scotland, was a shoemaker, but possessed great mechanical ingenuity. He could not keep his mind from the subject of mechanics. He devoted a great deal of time to designing mechanical schemes for Perpetual Motion. An account of his efforts is taken from "Percy Anecdotes." The device was exhibited in Edinburgh and amazing to state it attracted the attention of one of the greatest and most original scientists that ever lived, Sir David Brewster. It is from a letter written by Brewster, in 1818, to the "Annales de Chimie," that we get a description of the Spence invention. The editor of "Annales de Chimie," was evidently reluctant to publish any article concerning Perpetual Motion, and only the great fame of Sir David induced him to give space to the contribution. The article was first published in France, but it has, with an introductory statement by the editor, been translated into English, as follows: The reader will readily conclude that in publishing this article we are influenced solely by the great reputation of the learned contributor. Sir David writes from Edinburgh: [Illustration] I am almost afraid to inform you that at this moment in Edinburgh may be seen a machine, made by a shoemaker at Linlithgow, which realizes the perpetual motion. This effect is produced by two magnets A and B, acting alternately upon a needle _m n_, of which the point of attachment _n_ corresponds exactly with the axis around which turns the movable lever C D. When the needle _m n_ has been attracted into the position _m´ n_ by the action of the magnet B, and C D is in consequence found in C´ D´, a _substance_ connected with m n is interposed by mechanism between _m´ n_ and B. This substance has the property of intercepting, or rather of modifying the action of the magnet B, and this permits the other magnet A to draw the needle into the position _m´´ n_; but no sooner has it reached this point than a second plate or layer of the same substance places itself before magnet, and immediately B attracts anew the needle. [Illustration]