On the Connexion of the Physical Sciences

The law of electrical attraction and repulsion has been determined by suspending a needle of gum-lac horizontally by a silk fibre, the needle carrying at one end a piece of electrified gold leaf. A globe in the same or opposite electrical state when presented to the gold leaf will repel or attract it, and will therefore cause the needle to vibrate more or less rapidly according to the distance of the globe. A comparison of the number of oscillations performed in a given time at different distances will determine the law of the variation of the electrical intensity, in the same manner that the force of gravitation is measured by the oscillations of the pendulum. Coulomb invented an instrument which balances the forces in question by the force of the torsion of a thread, which consequently measures the intensity; and Sir William Snow Harris has constructed an instrument with which he has measured the intensity of the electrical force in terms of the weight requisite to balance it. By these methods it has been found that the intensity of electrical attraction and repulsion varies inversely as the square of the distance. However, the law of repulsive force is liable to great disturbances from inductive action, which Sir William Snow Harris has found to exist not only between a charged and neutral body, but also between bodies similarly charged; and that, in the latter case, the inductive process may be indefinitely modified by the various circumstances of the quantity and intensity of the electricity and the distance between the charged bodies.