[173] D. L. Webster and H. Clark, Proc. Nat. Acad., III (1917), 18. Also Webster, ibid., VI (1920), 26 and 639.

[174] Paper read before the Third Solvay Congress, 1921.

[175] Proc. Roy. Soc., XCIX (1921), 261. See also the same, January, 1924.

[176] Verh. der deutsch. phys. Ges., XV and XVI, 1914.

[177] Millikan and Bowen, Phys. Rev., January, 1924.

[178] Nichols and Tear, ibid., 1923.

[179] J. J. Thomson, Electricity and Matter, p. 9.

[180] Phys. Rev., II (1913), 109.

[181] Ann. d. Phys. (4), VIII (1902), 149.

[182] Drude, Lehrbuch der Optik (1906), p. 472.