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. Footnote 48: J. J. Thomson, _Phil. Mag._ 47, p. 253, 1899; _Conduction of Electricity through Gases_, p. 73, 1903. Footnote 49: Rutherford, _Phil. Mag._ Jan. 1899. Footnote 50: Townsend, _Phil. Mag._ Feb. 1901. Footnote 51: Rutherford, _Phil. Mag._ Nov. 1897, p. 144, Jan. 1899. Footnote 52: Townsend, _Phil. Trans._ A, p. 157, 1899. Footnote 53: McClung, _Phil. Mag._ March, 1902. Footnote 54: Langevin, _Thèse présentée à la Faculté des Sciences_, p. 151, Paris, 1902. Footnote 55: Owens, _Phil. Mag._ Oct. 1899. Footnote 56: Rutherford, _Phil. Mag._ p. 429, Nov. 1897. Footnote 57: Zeleny, _Phil. Trans._ A, p. 193, 1901. Footnote 58: Langevin, _C. R._ 134, p. 646, 1902. Footnote 59: Zeleny, _Phil. Mag._ July, 1898. Footnote 60: Rutherford, _Phil. Mag._ Feb. 1899. Footnote 61: Zeleny, _Phil. Trans._ 195, p. 193, 1900. Footnote 62: Langevin, _C. R._ 134, p. 646, 1902, and Thesis, p. 191, 1902. Footnote 63: Rutherford, _Proc. Camb. Phil. Soc._ 9, p. 410, 1898. Footnote 64: Langevin, Thesis, p. 190, 1902. Footnote 65: Helmholtz and Richarz, _Annal. d. Phys._ 40, p. 161, 1890. Footnote 66: Wilson, _Phil. Trans._ p. 265, 1897; p. 403, 1899; p. 289, 1900. Footnote 67: Thomson, _Phil. Mag._ p. 528, Dec. 1898. Footnote 68: Wilson, _Phil. Trans._ A, 193, p. 289, 1899. Footnote 69: Thomson, _Phil. Mag._ p. 528, Dec. 1898, and March, 1903. _Conduction of Electricity through Gases_, Camb. Univ. Press, 1903, p. 121. Footnote 70: Wilson, _Phil. Mag._ April, 1903. Footnote 71: Townsend, _Phil. Trans._ A, p. 129, 1899. Footnote 72: Townsend, _loc. cit._ p. 139. Footnote 73: Some difference of opinion has been expressed as to the value of _V_ required to produce ions at each collision. Townsend considers it to be about 20 volts; Langevin 60 volts and Stark about 50 volts. Footnote 74: Rutherford, _Phil. Mag._ Jan. 1899. Footnote 75: Rutherford, _Phil. Mag._ Jan. 1899. Footnote 76: Strutt, _Phil. Trans._ A, p. 507, 1901 and _Proc. Roy. Soc._ p. 208, 1903. Footnote 77: McClung, _Phil. Mag._ Sept. 1904. Footnote 78: Eve, _Phil. Mag._ Dec. 1904. Footnote 79: Rutherford, _Phil. Mag._ p. 137, Jan. 1899. Footnote 80: Child, _Phys. Rev._ Vol. 12, 1901. Footnote 81: Rutherford, _Phil. Mag._ p. 210, August, 1901; _Phys. Rev._ Vol. 13, 1901. Footnote 82: Rutherford, _Phil. Mag._ Aug. 1901. Footnote 83: