Page:Proceedings of the Royal Society of London Vol 69.djvu/440

422 influence of the electrical stress, likewise flew off, and were deposited in the metallic state near the pole.

An experiment was tried to discover if the ions of metal, deposited in this manner on a metal plate connected with an idle pole, in the full stream of + ions and - electrons, showed any special + or - electrification. In all cases the electrification was positive. This lends support to Mr. Strutt's view that + ions as well as - electrons will fly off from a radio-active body. Even these results, however, must not be taken as conclusive, for in a paper published in 1891,* I showed that at a high vacuum nearly the whole of the interior of a tube through which an induction spark was passing was electrified positively, negative electrification being detected only in the immediate neighbourhood of the negative pole.

During the course of my experiments a curious circumstance was observed, which deserves record as it may elucidate some of these obscure phenomena. While the volatilisation of the silver pole is rapidly proceeding, the metal glows as if red-hot. This " red heat" is superficial only. The metal instantly assumes, or loses, the appearance of red heat the moment the current is turned on or off, showing that the high temperature does not penetrate below the surface. The volatilisation of the positive ions is confined to the surface, and the surface glow is connected with that action. If instead of silver, a good conductor of heat, I take diamond, a bad conductor, the surface layers are changed sufficiently to convert them into a form of graphite,, which from its great resistance to oxidising agents, cannot be formed at a lower temperature than 3600 C.

After an account of the methods employed by previous experimenters in the subject, reference is made to the views of Nichols, according to which two distinct kinds of ice have been subjected to experiments. The density of artificial ice is about 0.916 gramme per cubic centimetre, while that of natural ice is more than one part in a thousand greater.


 * "Electricity in Transitu: from Plenum to Yacuum," 'Journ. lust. Elect. Engin.,' TO!. 20, p. 10.