Geological Society. 151 



limits the application of thermal diffusion as a separating 

 agent. I venture to publish this note, however, in the hope 

 that, apart from its theoretical interest,it may, perhaps, at some 

 time enable a partial separation of two gases to be produced 

 in difficult cases where this means, though a weak one, may 

 be the best available. Whether it has any application to the 

 radium products of nearly equal molecular weight, which 

 Prof. Soddy has stated to be difficult to separate, I am 

 personally unable to say. 

 Greenwich, March 1917. 



XV. JSotices respecting JSew Boohs. 



X-Rays and Crystal Structure. By W. H. Bragg, M.A., D.Sc, 

 F.R.S., and'L. W. Bragg, B.A. Pp. vih + 2^9. Loudon: 

 G. Bell & Sons, Ltd. 1915. 



A N admirable presentation of the theory and of the experimental 

 "£*- side of this recently discovered domain of diffraction phe- 

 nomena is given in an easily readable and very attractive manner. 

 The greater part of the volume is dedicated to the investigations of 

 the authors, whose merit in this rich field of research cannot be 

 overestimated. The volume can be warmly recommended to the 

 physicist as well as to the crystallographer and the chemist. 



XVI. Proceedings of Learned Societies. 



GEOLOGICAL SOCIETY. 

 [Continued from vol. xxxiii. p. 535.] 



February 16th, 1917.— Dr. Alfred Harker, F.B.S., President, 

 in the Chair. 



r PHE President proceeded to read his Anniversary Address, in- 

 -*- eluding first obituary notices of Jules Gosselet (elected Foreign 

 Member in 1885), J. W. Judd (el. Fellow 1865), J. H. Collins 

 (el. 1869), C. T. Clough (el. 18/5), Clement Eeid (el. 1875), 

 Bedford McNeill (el. 1888), H. Eosales (el. 1877), W. E. Koch 

 (el. 1869), C. Dawson (el. 1885), T. de Courcy Meade (el. 1891), 

 and others. 



The remainder of the Address dealt with some aspects of 

 igneous action in Britain, and especially its relation to crustal 

 stress and displacement. This relation appears not only in the 

 distribution of igneous activity in time and space, in the succession 

 of episodes, the habits of intrusions, etc., but also in the petro- 

 graphical facies of the igneous rocks themselves. The cause of 

 such relation was sought in the existence of extensive inter-crustal 

 regions in a partially molten state : that is, with some interstitial 

 fluid magma, which must normally be rich in alkaline silicates. 

 There will be a continual displacement of the interstitial magma 

 from places of greater stress to places of less stress, and certain 



