Villard, Société de Physique, July, 1900.

Geitel, Phys. Zeit. 2, p. 116, 1900.

C. T. R. Wilson, Proc. Camb. Phil. Soc. 11, p. 52, 1900. Proc. Roy. Soc. 68, p. 152, 1901.

Rutherford and Allan, Phil. Mag. Dec. 1902.

Patterson, Phil. Mag. August, 1903.

Harms, Phys. Zeit. 4, No. 1, p. 11, 1902.

Cooke, Phil. Mag. Oct. 1903.

Wilson, Proc. Roy. Soc. 69, p. 277, 1901.

Jaffé, Phil. Mag. Oct. 1904.

Patterson, Phil. Mag. Aug. 1903.