prior to the Introduction of the Potentials. 57 



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 7 

 discoveries of modern chemists and physicists, which have made 

 known to us various pairs of gases whose elasticity is destroyed 

 by their admixture in certain proportions an effect which could 

 not 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." J 



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 f 

 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 deter- 

 mination 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* he virtually establishes the result that the electric 



* Page 677. 



