29Mache, Wien. Ber. 113, p. 1329, 1904.30Curie and Laborde, C. R. 138, p. 1150, 1904.31Blanc, Phil. Mag. Jan. 1905.32Boltwood, Amer. Journ. Science, 18, Nov. 1904.33Elster and Geitel, Phys. Zeit. 4, p. 522, 1903.34Elster and Geitel, Phys. Zeit. 5, No. 1, p. 11, 1903.35Vincenti and Levi Da Zara, Atti d. R. Instit. Veneto d. Scienze, 54, p. 95, 1905.36Burton, Phil. Mag. Oct. 1904.37Elster and Geitel, Phys. Zeit. 6, No. 3, p. 67, 1905.38Rutherford and Allan, Phil. Mag. Dec. 1902.39Elster and Geitel, Phys. Zeit. 4, p. 138, 1902; 4, p. 522, 1903.40Saake, Phys. Zeit. 4, p. 626, 1903.41Simpson, Proc. Roy. Soc. 73, p. 209, 1904.42McLennan, Phys. Rev. 16, p. 184, 1903, and Phil. Mag. 5, p. 419, 1903.43McLennan, Phys. Rev. No. 4, 1903.