Notices respecting New Books. 819 



Concerning one point, Mr. Wellisch put3 a different inter- 

 pretation upon a statement of mine from that which I 

 intended. I remarked that from the experiments of Phillips 

 it would appear that at high temperatures the positive and 

 negative ions in air would have nearly the same mobilities. 

 It is assumed that this applies only to the ions while they 

 exist as ordinary ions. If at very high temperatures the 

 negative electron leaves the atom or radical, it is hardly 

 right to treat the electron as the whole ion, or electron and 

 atom as still an ordinary small ion. Mr. Wellisch regards 

 the experiments of EL A. Wilson and Moreau at hi&h tempe- 

 ratures showing a large mobility for the negative ion as 

 against my view. But the word ion bein^ used in two 

 different senses, there is not in reality the discrepance 

 indicated by Mr. Wellisch between experiment and my 

 statement. Y ours obediently, 



William Sutherland. 



Melbourne, Feb. 1910. 



LXXXIIL Notices respecting New Books. 

 Radioactivity and Geology. An Account of the Influence of Radio- 

 active Energy on Terrestrial History. By Prof. J. Joly, F.li.8. 

 Constable & Co. Ltd. 7s. 6d. nett. 

 "PROFESSOR JOEY'S book treats of a subject in its infancy 

 -*■ and as the first attempt to deal with cue of the most 

 remarkable developments of our time, its appearance will be 

 heartily welcomed. Jt consists of an extension and elaboration 

 of his now celebrated Presidential Address to Section C of the 

 British Association at Dublin. Ever since Professor Strut t 

 analysed the representative rocks of the earth's crust for radium, 

 and showed that the infinitesimal amounts of this element present 

 therein far more than accounted for all the heat lost by this planet 

 by radiation, it has been recognized that the former attempts to 

 apply the laws of physics to geolopy had been, as it were, rubbed 

 off the slate and a new clean surface prepared for the future. It 

 is on this dean sheet that Professor Joly writes. Barely seven 

 years have elapsed since the principles of radioactive change became 

 known, and in this short space they have become so well known 

 that in the two opening chapters everything that is essential to 

 their application is clearly and briefly explained. Professor Strutt, 

 to escape from the dilemma his own discovery had involved the 

 subject in, suggested that the crust of the earth alone contained 

 appreciable amounts of radium, and that below a depth of some 

 60 miles the core consisted of a different kind of material, not 

 containing radium, citing in support of this view those of Professor 

 Milne on the velocity of propagation of earthquakes. Joly, on the 

 other baud, favours the bolder and less arbitrary alternative that 

 so far from the earth growing cooler, it is actually growing hotter 

 in its interior. For radioactive energy to supply and maintain 



