[101]. If the apparatus is required to be air-tight, the gold-leaf system can be charged by means of a piece of magnetized steel wire, which is made to touch the rod R by the approach of a magnet.
[102]. It is sometimes observed that the motion of the gold-leaf, immediately after charging, is irregular. In many cases, this can be traced to air currents set up in the electroscope in consequence of unsymmetrical heating by the source of light used for illumination.
[103]. Wilson, Proc. Camb. Phil. Soc. Vol. 12, Part II. 1903.
[104]. Walker, Phil. Mag. Aug. 1903.
[105]. Strutt, Phil. Trans. A, p. 507, 1901.
[106]. Dolezalek, Instrumentenkunde, p. 345, Dec. 1901.
[107]. It is very desirable that care should be taken not to release large quantities of the radium emanation inside a laboratory. This emanation has a slow rate of decay and is carried by currents of air throughout the whole building and finally leaves behind an active deposit of very slow rate of change (see [chapter XI.]). Eve (Nature, March 16, 1905) has drawn attention to the difficulty of making refined radio-active measurements under such conditions.
[108]. J. J. Thomson, Phil. Mag. 46, p. 537, 1898.
[109]. Bronson, Amer. Journ. Science, Feb. 1905.
[110]. J. and P. Curie, C. R. 91, pp. 38 and 294, 1880. See also Friedel and J. Curie, C. R. 96, pp. 1262 and 1389, 1883, and Lord Kelvin, Phil. Mag. 36, pp. 331, 342, 384, 414, 453, 1893.