Intelligence and Miscellaneous Articles. 



603 



done"? As understood at the present day it asserts what this 

 quantitative relationship is. 



Professor Lewis obviously understands the mathematics which 

 he employs. His exposition of the meaning of a certain partial 

 differential coefficient in the footnote on p. 67 is a model of 

 lucidity, and will be of great use to those who are less familiar 

 with the matter than he is himself. 



The osmotic pressure of concentrated solutions is very fully 

 considered in its relation to other physical constants in Chap. VIII. > 

 while in Chap. X. there is a full account of chemical equilibrium 

 (from the thermodynamic standpoint) when capillary or electrical 

 effects are of importance ; including adsorption and Donnan's 

 theory of membrane equilibrium. There is still a great deal more 

 to be said about these latter subjects, but the account given is an 

 excellent digest of what is at present known. 



la Chapter XII. Nernst's heat theorem is considered. Part 111. 

 is devoted to considerations based upon thermodynamics and 

 statistical mechanics, including applications of the unitary theory 

 of energy (energy quanta) to physical and chemical problems. This 

 part is of very great interest. 



We have noticed no mistakes in typography. The references 

 are very complete. The illustrations are good. There is a subject 

 and an authors index which are well compiled. Professor Lewis 

 is to be congratulated in all respects. 



LXVI. Intelligence and Aliscellaneous Articles. 



REFRACTION OF X-RADIATION. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, — 



HHHE experiments carried out by Professor Earkla to detect the 

 •*■ refraction of X-rays (Phil. Mag. April 1916) have led to 

 results which show that the refractive index of potassium 

 bromide for X-radiation (A= *5 x 10~ s cm.) is between '999995 

 and 1-000005. 



In the year 1914 I carried out a series of experiments in the 

 Physical Laboratory of the University of Birmingham, in which 

 it was attempted to refract a beam of X-radiation by passing 

 it through a system of prisms. The refracting materials used for 

 constructing the prisms were lead, aluminium, and sulphur. The 

 two former were carefully shaped on a milling machine from solid 

 blocks of material, while the sulphur prisms were prepared by 

 casting, using the metallic prisms as moulds. No attempt was 

 made to use optically worked surfaces. Owing to the acquisition 

 of the University buildings by the War Office for the purposes of 

 a military hospital, these experiments were discontinued on the 



