concentrated chiefly on the negative electrode in an electric field (see chapter VIII).
An experiment to illustrate the phosphorescence produced in some substances by the rays from a large amount of emanation is described in section 165.
148. Curie and Debierne12 have investigated the emanation from radium, and the excited activity produced by it. Some experiments were made on the amount of emanation given off from radium under very low pressures. The tube containing the emanation was exhausted to a good vacuum by a mercury pump. It was observed that a gas was given off from the radium which produced excited activity on the glass walls. This gas was extremely active, and rapidly affected a photographic plate through the glass. It caused fluorescence on the surface of the glass and rapidly blackened it, and was still active after standing ten days. When spectroscopically examined, this gas did not show any new lines, but generally those of the spectra of carbonic acid, hydrogen, and mercury. In the light of the results described in section 124 the gas, given off by the radium, was probably the non-active gases hydrogen and oxygen, in which the active emanation was mixed in minute quantity. It will be shown later (section 242) that the energy radiated from the emanation is enormous compared with the amount of matter involved, and that the effects observed, in most cases, are produced by an almost infinitesimal amount of