35.] The importance which Maxwell attached to the study of the phenomena attending the passage of electricity through gases, as well as the fact that there is no summary in English text books of the very extensive literature on this subject, lead me to think that a short account of recent researches on this kind of electric discharge may not be out of place in this volume.

Can the Molecule of a Gas be charged with Electricity?

36.] The fundamental question as to whether a body if charged to a low potential and surrounded by dust-free air at a low temperature will lose any of its charge, and the very closely connected one as to whether it is possible to communicate a charge of electricity to air in this condition, have occasioned considerable divergence of opinion among physicists.

Coulomb (Mémoïres de l'Académie des Sciences, 1785, p. 612), who investigated the loss of electricity from a charged body suspended by insulating strings, thought that after allowing for the leakage along the supports there was a balance over, which he accounted for by a convective discharge through the air; he supposed that the particles of air when they came in contact with a charged body received a charge of electricity of the same sign as that on the body, and that they were then repelled by it. On this view the molecules of air, just like small pieces of metal, can be charged with electricity.