Footnote 120: M. and Mme Curie, _C. R._ 130, p. 647, 1900. Footnote 121: The activity of the radium preparation was not stated in the paper. Footnote 122: Dorn, _Phys. Zeit._ 4, No. 18, p. 507, 1903. Footnote 123: Strutt, _Phil. Mag._ Nov. 1903. Footnote 124: Wien, _Phys. Zeit._ 4, No. 23, p. 624, 1903. Footnote 125: Dorn, _C. R._ 130, p. 1129, 1900. Footnote 126: Becquerel, _C. R._ 130, p. 809, 1900. Footnote 127: Kaufmann, _Phys. Zeit._ 4, No. 1 b, p. 54, 1902. Footnote 128: Abraham, _Phys. Zeit._ 4, No. 1 b, p. 57, 1902. Footnote 129: Kaufmann, _Nachrichten d. Ges. d. Wiss. zu Gött._, Nov. 8, 1901. Footnote 130: Simon, _Annal. d. Phys._ p. 589, 1899. Footnote 131: Kaufmann, _Phys. Zeit._ 4, No. 1 b, p. 54, 1902. Footnote 132: Paschen, _Annal. d. Phys._ 14, p. 389, 1904. Footnote 133: Meyer and Schweidler, _Phys. Zeit._ pp. 90, 113, 209, 1900. Footnote 134: Lenard, _Annal. d. Phys._ 56, p. 275, 1895. Footnote 135: Strutt, _Nature_, p. 539, 1900. Footnote 136: Seitz, _Phys. Zeit._ 5, No. 14, p. 395, 1904. Footnote 137: It is presumed that the results were corrected, if necessary, for the discharging action due to the ionized gas, although no direct mention of this is made in the paper by Seitz. Footnote 138: Strutt, _Phil. Trans._ A, p. 507, 1901. Footnote 139: Crookes, _Proc. Roy. Soc._ 1902. _Chem. News_, 85, p. 109, 1902. Footnote 140: Mme Curie, _C. R._ 130, p. 76, 1900. Footnote 141: Rutherford, _Phil. Mag._ Feb. 1903. _Phys. Zeit._ 4, p. 235, 1902. Footnote 142: Becquerel, _C. R._ 136, p. 199, 1903. Footnote 143: Becquerel, _C. R._ 136, p. 431, 1903. Footnote 144: Des Coudres, _Phys. Zeit._ 4, No. 17, p. 483, 1903. Footnote 145: Becquerel, _C. R._ 136, p. 1517, 1903. Footnote 146: Bragg, _Phil. Mag._ Dec. 1904; Bragg and Kleeman, _Phil. Mag._ Dec. 1904. Footnote 147: Further experimental results bearing on this important question are given in an Appendix to this book. Footnote 148: Bakerian Lecture, _Phil. Trans._ A, p. 169, 1904. Footnote 149: Strutt, _Phil. Mag._ Aug. 1904. Footnote 150: J. J. Thomson, _Proc. Camb. Phil._ Soc. 13, Pt. I. p. 39, 1905. _Nature_, Dec. 15, 1904. Footnote 151: Rutherford, _Nature_, March 2, 1905. J. J. Thomson, _Nature_, March 9, 1905. Footnote 152: Crookes, _Proc. Roy. Soc._ 81, p. 405, 1903. Footnote 153: Elster and Geitel, _Phys. Zeit._ No. 15, p. 437, 1903. Footnote 154: Glew, _Arch. Röntgen Ray_, June 1904. Footnote 155: Becquerel, _C. R._ 137, Oct. 27, 1903. Footnote 156: Tommasina, _C. R._ 137, Nov. 9, 1903. Footnote 157: An interesting side-light is thrown on this question by the experiments described in Appendix A of this book. Footnote 158: Rutherford and Miss Brooks, _Phil. Mag._ July 1902. Footnote 159: