s a machine so called from its inventor, who asserted it to be a perpetual motion. This machine, according to the account given of it by s'Gravesande, in his Œuvres Philosophiques, consisted externally of a large circular wheel, or rather drum, twelve feet in diameter, and fourteen inches deep, being very light, as it was formed of an assemblage of deals, having the intervals between them covered with waxed cloth, to conceal the interior parts of it. The two extremities of an iron axis, on which it turned, rested on two supports. On giving a slight impulse to the wheel in either direction, its motion was gradually accelerated; so that after two or three revolutions it acquired so great a velocity as to make twenty-five or twenty-six turns in a minute. This rapid motion it actually preserved during the space of two months, in a chamber of the landgrave of Hesse, the door of which was kept locked, and sealed with the landgrave's own seal. At the end of that time, however, it was stopped, to prevent the wear of the materials. The professor, who had been an eye-witness of these circumstances, examined all the external parts of it, and was convinced that there could not be any communication between it and any neighbouring room. Orffyreus, however, was so incensed, or pretended to be so, that he broke the machine in pieces, and wrote upon the wall that it was the impertinent curiosity of Professor s'Gravesande which made him take this step.