Another interesting action of the radium rays has been observed by Giesel. On bringing up a radium preparation to the closed eye, in a dark room, a sensation of diffuse light is observed. This effect has been examined by Himstedt and Nagel[223] who have shown that it is due to a fluorescence produced by the rays in the eye itself. The blind are able to perceive this luminosity if the retina is intact, but not if the retina is diseased. Hardy and Anderson[224] have examined this effect in some detail. The sensation of light is produced both by the β and γ rays. The eyelid practically absorbs all the β rays, so that the luminosity observed with a closed eye is due to the γ rays alone. The lens and retina of the eye are strongly phosphorescent under the action of the β and γ rays. Hardy and Anderson consider that the luminosity observed in a dark room with the open eye (the phosphorescent light of the radium itself being stopped by black paper) is to a large extent due to the phosphorescence set up in the eyeball. The γ rays, for the most part, produce the sensation of light when they strike the retina. Tommasina stated that the air exhaled by man contained a larger proportion of ions than ordinary air, and, in consequence, caused an increased rate of discharge of an electroscope. The experiment was repeated by Elster and Geitel but with negative results. On the other hand, they found that the breath of Dr Giesel, of Braunschweig, who had been engaged continuously in the chemical separation of the radio-active bodies, caused a rapid loss of charge of an electroscope. This increased rate of discharge was probably mainly due to the radium emanation, with which his system had become impregnated by inhaling the emanation-laden air of the laboratory. Footnote 184: Becquerel, _C. R._ 129, p. 912, 1899. Footnote 185: Bary, _C. R._ 130, p. 776, 1900. Footnote 186: Kunz and Baskerville, _Amer. Journ. Science_ XVI. p. 335, 1903. Footnote 187: See _Nature_, p. 523, March 31, 1904. Footnote 188: Crookes, _Proc. Roy. Soc._ 74, p. 47, 1904. Footnote 189: Kunz and Baskerville, _Science_ XVIII, p. 769, Dec. 18, 1903. Footnote 190: Beilby in a recent communication to the Royal Society (Feb. 9 and 23, 1905) has examined in some detail the production of phosphorescence by the β and γ rays of radium and has put forward a theory to account for the different actions observed. Footnote 191: Huggins, _Proc. Roy. Soc._ 72, pp. 196 and 409, 1903. Footnote 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. Footnote 193: Giesel, _Ber. d. D. Chem. Ges._ 37, p. 1696, 1904. Footnote 194: