Notices respecting New Boohs. 675 



(ii.) The absorbability of the secondary radiation varies 

 with the nature of the gas. In general it is similar in 

 character to the secondary radiation given off by the same 

 element in the solid state. 



(iii.) For a given primary radiation and a given gas, the 

 intensity of secondary radiation is proportional to the pressure 

 of the o-as. It varies with the nature of the gas and does not 

 in general follow any " density ' law. 



(iv.) The secondary radiation from a molecule of gas is 

 the sum of the secondary radiations from the atoms composing- 

 it. For a given primary radiation, the secondary radiation 

 from a given element in the gaseous state depends only upon 

 the mass of it present, and not upon its state of chemical 

 combination. 



(v.) Gases may be divided into two classes according as 

 they merely scatter, or transform the primary radiation. 

 For the former class, which contains the elements with an 

 atomic weight less than that of sulphur, the secondary 

 radiation per atom is proportional to the atomic weight, with 

 the exception of hydrogen. Elements of higher atomic 

 weight give oft' secondary radiation in very much larger 

 amounts and generally of a much softer character. 



(vi.) The ratio of the intensities of the primary and secondary 

 beam is independent of the intensity of the primary rays, and 

 generally of their hardness. For some gases, however, the 

 intensity of the secondary beam increases as the hardness of 

 the primary rays is increased. 



In conclusion I wish to express my best thanks to 

 Prof. J. J. Thomson, at whose suggestion the subject of this 

 research was undertaken, for his helpful interest and 

 unfailing kindness throughout the course of a long and 

 difficult research. 



Cavendish Laboratory, Cambridge, 

 24th July, 1907. 



LXV. Notices respecting New Books. 



Bases Physiques de la Musique. Par M. H. Bouasse, Professeur 

 a la Faculte des Sciences de Toulouse. Paris : G-authier-Villars. 

 1907. Pp. 110. 

 r PHIS interesting monograph will be found very useful by those 

 -■- who, while desirous of acquiring some knowledge of the physical 

 basis of music, arc leterred from a study of it by the somewhat 

 forbidding aspect of standard treatises, among which the first place 

 must be assigned to Helmholtz's great work. The author accepts 

 all the main conclusions arrived at by Helmholtz, but succeeds in 

 treating the subject iu a manner so clear and interesting that it 



