While Perpetual Motion seemed to have received considerable time and attention from him, and while his writings show that he examined a great many mechanical devices, he seems all the time to have entertained serious doubt of the possibility of a machine having self-motive power. However, in 1770, he devised a machine for the purpose of producing Perpetual Motion. It does not appear that he ever offered the machine to the public, or sought publicity for it. A description of it is to be found in his Common Place Book in the University Library, Edinburg. The description there furnished is as follows: The axle at A is placed horizontally, and the spokes B, C, D, etc., turn in a vertical position. They are jointed at _s_, _t_, _u_, etc., as a common sector is, and to each of them is fixed a frame as R, S, T, etc., in which the weights 7, 8, 9, 1, 2, etc., have liberty to move. When any spoke as D is in a horizontal position, the weight I in it falls down and pulls the part _b_ of the then vertical spoke B straight out, by means of a cord going over the pulleys K and k to the weight I. The spoke C _c_ was pulled straight out before, when it was vertical, by means of the weight 2, belonging to the spoke E _e_ which is in the horizontal position D _d_; and so of all the others on the right hand. But when these spokes come about to the left hand, their weights 4, 5, 6 fall back, and cease pulling the parts _f_, _g_, _h_, _i_; so that the spokes then bend at their joints X, _y, z_, and the balls at their ends come nearer the center A, all on the left side. Now, as the balls or weights at the right hand side are farther from the center A than they are on the left, it might be supposed that this machine would turn round perpetually. I have shown it to many who have declared it would; and yet for all that, whoever makes it, will find it to be only a mere balance. I leave them to find out the reason. B. Belidor's Device This device was incubated in the brain of an American. His name is unknown. We have denominated it "B. Belidor's Device," not because B. Belidor was the inventor, but because the account of the invention was furnished by him. This device seems to the author to have possessed originality, though, of course, it failed to work for reasons clearly apparent. [Illustration] An account of it was given in the Journal of Franklin's Institute, Philadelphia, in 1828. The article contributed by B. Belidor is as follows: Even the pursuit after perpetual motion, hopeless as it is, may not be considered entirely vain, in occasionally leading to useful modifications of machinery. As an instance of this, I here submit to you a plan suggested by an ingenious friend of mine, several years ago, as in the diagrams annexed, Fig. 1, a perpendicular, and Fig. 2 a horizontal view.