The celebrated problem of a self-impelling power, though denied by Huygens and de la Hire, who have attempted to demonstrate its fallacy, has yet been supported by some of the most celebrated among the ancient as well as modern philosophers. Innumerable have been the machines to which the idea of _the perpetual motion_ has given birth; but the most celebrated among the moderns is the _Orffyrean wheel_. This machine, according to the description given of it by M. Grævesande, in his _Œuvres Philosophiques_, consisted of a large circular wheel or drum, twelve feet in diameter, and fourteen inches in depth. It was composed of a number of thin deals, the spaces between which were covered with wax cloth, in order to conceal the interior parts of it. On giving the wheel, which rested on the two extremities of an iron axis, a slight impulse in either direction, its motion was gradually accelerated; so that after two or three revolutions it is said to have acquired so great a velocity as to make twenty-five or more turns in a minute: and it appears to have preserved this rapid motion for the space of two months, during which time the Landgrave of Hesse, in whose chamber it was placed to prevent a possibility of collusion, kept his own seal on the outer door. At the end of that time it was stopped to prevent the wear of the materials. Grævesande, who had been an eye-witness to the performance of this machine, examined all the external parts of it, and was convinced that there could not be any communication between it and the adjacent rooms. Orffyreus, however, having been informed of the ill-timed curiosity of the professor, and incensed at the refusal of a premium of _twenty thousand pounds_, which he had made a _sine quâ non_ for disclosing the mechanism of its construction, broke the whole apparatus into atoms, and his life was soon after sacrificed to chagrin at his disappointment. The analogy between the Marquis's description and the Orffyrean wheel is sufficiently evident; and the experiment having been made in the Tower, more than fifty years prior to the attempt of the German mechanic, it is more than probable that the idea was derived from the noble author's work. No. LVII.