supposing that there are two electric fluids, the parts of the same fluid repelling each other according to the inverse square of the distance, and attracting the parts of the other fluid according to the same inverse square law." "The supposition of two fluids," he adds, "is moreover in accord with all those discoveries of modern chemists and physicists, which have made known to a various pairs of gases whose elasticity is destroyed by their admixture in certain proportions—an effect which could pot take place without something equivalent to a repulsion between the parts of the same gas, which is the cause of its elasticity, and an attraction between the parts of different gases, which accounts for the loss of elasticity on combination."
According, then, to the two-fluid theory, the "natural fluid" contained in all matter can be decomposed, under the influence of an electric field, into equal quantities of vitreous and resinous electricity, which, if the matter be conducting, can then fly to the surface of the body. The abeyance of the characteristic properties of the opposite electricities when in combination was sometimes further compared to the neutrality manifested by . the compound of an acid and an alkali.
The publication of Coulomb's views led to some controversy between the partisans of the one-fluid and two-fluid theories; the latter was soon generally adopted in France, but was stoutly opposed in Holland by Van Marum and in Italy by Volta. The chief difference between the rival hypotheses is that, in the two-fluid theory, both the electric fluids are movable within the substance of a solid conductor; while in the one-fluid theory the actual electric fluid is mobile, but the particles of the conductor are fixed. The dispute could therefore be settled only by a determination of the actual motion of electricity in discharges; and this was beyond the reach of experiment.
In his Fourth Memoir Coulomb showed that electricity in equilibrium is confined to the surface of conductors, and does not penetrate to their interior substance; and in the Sixth Memoir[1] he virtually establishes the result that the electric
- ↑ Page 677.
