Thus, even though the facts of electrolysis give us no information at all as to how much of a charge one electron represents, they do tell us very exactly that if we should take as many times as there are molecules in a gram molecule we should get exactly 9,650 absolute electromagnetic units of electricity. This is the amount of electricity conveyed by a current of 1 ampere in 10 seconds. Until quite recently we have been able to make nothing better than rough guesses as to the number of molecules in a gram molecule, but with the aid of these guesses, obtained from the Kinetic Theory, we have, of course, been enabled by (1) to make equally good guesses about . Those guesses, based for the most part on quite uncertain computations as to the average radius of a molecule of air, placed anywhere [Pg 32] between and . It was in this way that G. Johnstone Stoney in 1874 estimated at . In O. E. Meyer’s Kinetische Theorie der Gase (p. 335; 1899), , the number of molecules in a cubic centimeter, is given as . This would correspond to . In all this is the charge carried by a univalent ion in solution and or is a pure number, which is a characteristic gas constant, it is true, but the analysis has nothing whatever to do with gas conduction. III. THE NATURE OF GASEOUS CONDUCTION The question whether gases conduct at all, and if so, whether their conduction is electrolytic or metallic or neither, was scarcely attacked until about 1895. Coulomb in 1785 had concluded that after allowing for the leakage of the supports of an electrically charged conductor, some leakage must be attributed to the air itself, and he explained this leakage by assuming that the air molecules became charged by contact and were then repelled—a wholly untenable conclusion, since, were it true, no conductor in air could hold a charge long even at low potentials, nor could a very highly charged conductor lose its charge very rapidly when charged above a certain potential and then when the potential fell below a certain critical value cease almost entirely to lose it. This is what actually occurs. Despite the erroneousness of this idea, it persisted in textbooks written as late as 1900. Warburg in 1872 experimented anew on air leakage and was inclined to attribute it all to dust particles. The real explanation of gas conduction was not found until after the discovery of X-rays in 1895. [Pg 33] The convincing experiments were made by J. J. Thomson, or at his instigation in the Cavendish Laboratory at Cambridge, England. The new work grew obviously and simply out of the fact that X-rays, and a year or two later radium rays, were found to discharge an electroscope, i.e., to produce conductivity in a gas. Theretofore no agencies had been known by which the electrical conductivity of a gas could be controlled at will.