﻿Notices respecting New Books. 1057 



that perpetual re-writing would be required iu order to assimilate 

 it completely. These sections of the book happen to include 

 those which will be perused with the greatest interest by readers 

 of the Philosophical Magazine, in which Magazine so much of 

 this newer knowledge has been published. Thus, on page 104 an 

 estimate of the Avogadro Constant is given which dates from 

 1899, although later determinations are quoted on pp. G39 and 

 753. Again, the whole of the sections on the Atomic Theory 

 are based on the conceptions of 20 years ago, before the 

 complications arising from the discovery of the radio elements and 

 of isotopes had arisen, and before the simplifying factors intro- 

 duced by the experimental determining of atomic numbers had 

 appeared or made their influence felt. Strictly speaking, this 

 -omission applies only to the text, since the list of International 

 Atomic Weights on page 199 and the Periodic Table on page 256 

 have been revised to include Atomic Numbers, as well as Atomic 

 Weights ; but these are not referred to in the index nor explained 

 in the text, although atomic numbers are mentioned on page 255 

 and isotopes on page 266 as subjects for discussion in a future 

 volume. In view of the masterly way in which he has dealt with 

 other subjects, there can be little doubt that these later discoveries 

 will be adequately described and discussed in the volume which 

 deals with the radioactive elements ; but there are many para- 

 graphs, such as the one on page 200, where the inquiry is made 

 as to whether the atomic weights are whole numbers, which would 

 certainly have been written otherwise if the facts in reference 

 to isotopes had been known when the text was first drafted. 

 Again, a considerable part of the author's very able discussion of the 

 classification of the elements is tedious to the point of positive 

 irritation to a reader who is accustomed to see all these problems 

 simplified, even if not completely solved, with the help of atomic 

 numbers. The fact that certain of these sections are already out 

 of date, if not actually incorrect, is part of the penalty which 

 must be exacted from anyone who insists on being the author 

 rather than the editor of a " Comprehensive Treatise " on a rapidly 

 growing science with two thousand years of history behind it. It 

 is necessary to add that the chapter on Crystals and Crystallization 

 bears no evidence of being rendered obsolete or of requiring to be 

 re-written in the light of modern work on the analysis of crystal 

 structure by X-rays, of which a satisfactory summary is given, 

 including references as recent as 1920. Moreover, the author's 

 reputation, both as a mathematician and as a physical chemist, is 

 a sufficient guarantee of the adequate treatment of subjects such 

 as reaction velocities and energetics, where there is no risk of 

 obsolescence arising from rapid new developments, so that 

 the problems can be reviewed and the sections written up at 

 leisure. 



The chemical, as contrasted with the physical, portion of the 

 work calls for nothing but admiration ; and whilst the Treatise 



