Intelligence and Miscellaneous Articles. 707 



to practical work in crystallography ; it includes also all the 

 essential theory of the subject not only as regards crystal 

 morphology but also with regard to the physical properties of 

 crystals. It is, of course, to the latter that we must give first place 

 in this review. This may for our purpose be divided into two 

 parts. There is the part in which Dr. Ttttton describes the optical 

 properties of crystals especially in relation to polarized light. 

 This part is most excellently done. Dr. Tutton is fully familiar 

 with this part of his subject, and he has not failed to give a very 

 lucid and full account of it. This part, like all the rest of the 

 volume, is very fully illustrated. The illustrations are good, the 

 majority of them being quite new. Many of them are from 

 photographs by Dr. Tutton himself ; these have been taken with 

 great skill, and the publishers have reproduced them with great 

 success. The perspective views, on page 595, of a prism refracting 

 light arc perhaps not as happily conceived as most. Even if they 

 may suggest the phenomenon better to some readers, it is probable 

 that most would understand better a plane sectional drawing such 

 as is usually given. This part of the book fills some hundreds of 

 pages and is replete with details, that have never been brought 

 together in the same way before, of methods of measuring 

 refractive indices, optic axial angles, and other data of crystals. 

 In another part Dr. Tutton is not quite so happy. This is when 

 he is giving a summary of what may be described as outlying 

 phenomena such as the Zeeman effect. This criticism may be 

 made of Chapter xxxiv ; but, as most of this chapter is in small 

 print, it is clear that the author intends it to take only a 

 secondary place ; and we will leave it in such a position in this 

 notice. On the crystallographic side Dr. Tutton gives a full 

 account of the characteristics of the various crystals and of the 

 methods of representing them in stereographic projections. This 

 account has not been unnecessarily encumbered with antiquated 

 phraseology ; indeed, the author's attempt has been to lighten the 

 subject as much as possible in this respect. It is needless to say 

 that the conception of molecular distance ratios occupies a 

 prominent place. 



Dr. Tutton is a practical worker, and without hesitation we say 

 that he has produced a most practical guide to this subject. 



LXX. Intelligence and Miscellaneous Articles. 



NOTE ON THE DIFFUSION Of ALKALI SALT VAPOURS IN FLAMES 

 AND ON THF, MEASUREMENT OF THE VELOCITY OF FLAMES. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, — 

 TN a paper published in your July number on " The Diffusion of 

 Alkali Salt Vapours in Flames," Prof. H. A. Wilson commu- 

 nicates experiments undertaken with the object of finding the 

 coefficients of diffusion of these vapours in a Bunsen flame. A 

 small bead of salt on a platinum wire is put in the flame, and the 



