Construction et usage d'une balance électrique, fondée sur la propriété qu'ont les fils de métal, d'avoir une force de réaction de torsion proportionnelle à l'angle de torsion

Abstract

In a memoir presented to the Academy, in 1784, I have determined from experiments the laws governing the torsional resistance of a filament of metal and I have found that this force is proportional to the angle of torsion, to the fourth power of the diameter of the suspended filament and inversely proportional to its length - all multiplied by a constant coefficient which depends on the nature of the metal and is easily determined by experiment. I have shown in the same Memoir that by means of this force of torsion, it was possible to precisely measure extremely small forces as, for example, one ten thousandths of a grain1. In the same Memoir I described a first application of this theory, seeking to evaluate the constant force attributed to adhesion in the formula for the surface friction of a solid body moving through a fluid. Today, I set before the eyes of the Academy, an electric balance constructed according to the same principles. It measures with the greatest precision the state and the electric force of a body, however weak the degree of electricity.