[41]. Hofmann, Gonder and Wölfl, Annal. d. Phys. No. 13, p. 615, 1904.
[42]. Hofmann and Zerban, Ber. d. D. Chem. Ges. No. 12, p. 3093, 1903.
[43]. Baskerville and Zerban, Amer. Chem. Soc. 26, p. 1642, 1904.
[44]. J. J. Thomson and Rutherford, Phil. Mag. Nov. 1896.
[45]. The word ion has now been generally adopted in the literature of the subject. In using this word, it is not assumed that the ions in gases are the same as the corresponding ions in the electrolysis of solutions.
[46]. A minute current is observed between the plates even if no radio-active matter be present. This has been found to be due mainly to a slight natural radio-activity of the matter composing them. (See [chapter XIV.])
[47]. This nomenclature has arisen from the similarity of the shape of the current-voltage curves to the magnetization curves for iron. Since, on the ionization theory, the maximum current is a result of the removal of all the ions from the gas, before recombination occurs, the terms are not very suitable. They have however now come into general use and will be retained throughout this work.
[48]. J. J. Thomson, Phil. Mag. 47, p. 253, 1899; Conduction of Electricity through Gases, p. 73, 1903.
[49]. Rutherford, Phil. Mag. Jan. 1899.
[50]. Townsend, Phil. Mag. Feb. 1901.