Gravitation and Thermodynamics

Abstract

As pointed out by Sir Oliver Lodge in NATURE of April 5, the case I cited of a disc pivoted about its centre of mass and started in motion does not lead to perpetual motion in the ordinary sense. But, as it seems to me, there will be long-sustained, oscillatory, motion. On rotating the disc by a small angle, the descending half will gain, and the ascending half will lose, heat. A turning-moment will arise, and will increase until the angle turned is Ï/2. It will then decrease until, when the angle turned is Ï, the moment is nil. This position gives the condition, quoted by Sir Oliver Lodge, of thermal symmetry about the vertical diameter of the disc. As the disc continues to rotate, due to its momentum, a moment in a reverse sense will be set up, so that when the whole rotation is nearly 2Ï, the rotation will be reversed. We shall thus obtain an oscillatory motion, long sustained if small friction is involved. In the final position the disc will have rotated from its initial position by angle Ï. Such a result would be phenomenal, since the mere act of rotating the disc by an infinitesimal angle would, in effect, convert a condition of neutral, into one of unstable, equilibrium.