[19] L. B. Loeb, Jour. Franklin Inst., CXCVII (1924), 45.

[20] H. A. Erikson, Phys. Rev., XX (1922), 118.

[21] H. B. Wahlin, ibid., p. 267.

[22] Verb. der deutsch. phys. Ges., XI (1909), 146 and 276.

[23] Proc. Roy. Soc., LXXX (1908), 207.

[24] Fournier d’Albe, Life of Sir William Crookes, 1924.

[25] Proc. Roy. Soc., XL (1890), 526.

[26] Phil. Mag., XLIV (1897), 298.

[27] W. Wien, Wied. Ann., LXV (1898), 440.

[28] Rays of Positive Electricity. London: Longmans, 1913.