[451]. See article in Le Radium, No. 3, p. 81, Sept. 15, 1904.

[452]. J. J. Thomson, Proc. Camb. Phil. Soc. 12, p. 391, 1904.

[453]. Wood, Phil. Mag. April, 1905.

[454]. Campbell, Nature, p. 511, March 31, 1904. Phil. Mag. April, 1905.

[455]. An apparent exception has been observed by Danne in the case of certain lead minerals which occur under peculiar conditions at d’Issy-l’Évêque, France. See p. [465].