Notices respecting New Books. ;>S3 



Shortly after coming to these views I noticed in ZirkePs 

 line monograph ' tfber Uransscheidungen in Rheinischen 

 Basalten ' (p. 52) the remark that the large zircons in these 

 basalts may, by aid o£ a lens, be seen to be bordered by a 

 thin dark grey margin. He remarks that this border is 

 about O05 mm. wide. There can be little doubt that rhis 

 is of similar origin to the halo in biotite. 



The question remains, what is the precise nature of these 

 halos ? It is certainly not a colouration similar to the 

 colouration produced in glass by radium. The latter takes 

 place through very considerable thicknesses and is, therefore, 

 ascribed to the (3 radiation. While it is worth consideration 

 if the deep brown of certain biotites, much spotted by halos, 

 is not a potassium colouration referable to the ionizing 

 influence of ft rays (see the interesting paper of Mr. J. C. 

 Maxwell Garnett, Phil. Trans. Roy. Soc. vol. 205), the limited 

 radius of the halo and its particular limiting value point to 

 the a, radiation as being responsible. Helium is probably 

 stored in the halo but in very minute quantity. Thus it is 

 -easily calculated that if an average halo-sphere is derived 

 from a zircon having a diameter one-tenth of the sphere, a 

 period of 10 9 years must elapse to generate a quantity of 

 helium sufficient to fill one hundred thousandth part of the 

 volume of the sphere. 



Halos occur in cordierite which appear to differ somewhat 

 in properties from those in mica. I have no experience of 

 them : the cordierite in my possession showing many inclusions 

 but no halos. The inclusions apppear to be non-radioactive 

 substances. On the other hand, Dana makes the remark 

 that halos in cordierite are formed " particularly by zircon. ' 

 MM. Fouque and Levy speak of mica and pleonaste being- 

 associated with such halos. The first might well be radio- 

 active. The last mineral, which is very varia ble in composition, 

 I have not yet investigated. 



Geological Laboratory, 

 Trinity College, Dublin. 



XXX. Notices respecting New Boohs. 



La Mecanique des Phenomenes Fondee sur les Analogies. Par M. M. 

 Petrovitch, Professeur a FUniversite de Belgrade. Paris : 

 G-authier-\ r illars. 1906. Pp. 96. 



HPHE unity introduced into the investigation of physical phe- 

 •*- nomena by the use of analytical methods, which enable whole 

 series of physical problems to be thrown into identically the same 

 mathematical form, has long been known as an illustration of the 



