[191]. Huggins, Proc. Roy. Soc. 72, pp. 196 and 409, 1903.
[192]. The spark spectrum of the radium bromide showed the H and K lines of calcium and also faintly some of the strong lines of barium. The characteristic lines of radium of wave-lengths 3814·59, 3649·7, 4340·6 and 2708·6, as shown by Demarçay and others are clearly shown in the figure. The strong line of wave-length about 2814 is due to radium.
[193]. Giesel, Ber. d. D. Chem. Ges. 37, p. 1696, 1904.
[194]. Hartmann, Phys. Zeit. 5, No. 18, p. 570, 1904.
[195]. In a recent paper, Giesel (Ber. d. D. Chem. Ges. No. 3, p. 775, 1905) has shown that the bright lines are due to didymium, which is present as an impurity. Exposure of didymium to the radium rays also causes the appearance of the lines.
[196]. Wiedemann and Schmidt, Wied. Annal. 59, p. 604, 1895.
[197]. Wiedemann, Phys. Zeit. 2, p. 269, 1901.
[198]. Elster and Geitel, Annal. d. Phys. 69, p. 673, 1899.
[199]. Willons and Peck (Phil. Mag. March, 1905) found that under some conditions, especially for long sparks, the rays of radium hindered the passage of the spark.
[200]. Hemptinne, C. R. 133, p. 934, 1901.