334 SCIENCE PROGRESS 



confusing in some formulas. The number of typographical errors which we have 

 noticed throughout the book is very large. On the other hand, the greater part 

 of the application of the formulas to the observational material will be found to be 

 of considerable interest. The portion dealing with simple vortex systems shows 

 how the results have been used in weather prediction with considerable success. 

 The material provided by one of the international balloon ascents is fully worked 

 out and the method of deriving the radiation and circulation at different levels 

 explained. It appears that progress in theoretical meteorology is now largely 

 dependent upon a considerable extension of balloon observations taken with 

 self-recording instruments up to as high an altitude as possible. The value of a 

 knowledge of the prevailing conditions in the upper atmosphere which may be 

 thus derived will be of great value in weather forecasting. 



One of the subjects very fully discussed is the value of the " solar constant " of 

 radiation. Various authorities claim that the value approximates to 2'oo calories, 

 others that it is 400 calories. Which of these values is correct depends upon 

 whether there is an inappreciable loss of radiation in the very high cirrus layers 

 of the atmosphere or whether about half the radiation is there reflected back into 

 space. Prof. Bigelow inclines to the latter view and the higher value of the 

 constant, but the matter cannot yet be regarded as at all settled. Much more 

 work needs to be done by self-recording balloon pyrheliometers reaching to very 

 high altitudes. Valuable work is being done in this direction by C. G. Abbott of 

 the Smithsonian Institution, who strongly supports a value slightly less than 

 2 calories for the solar constant. 



We could wish that Prof. Bigelow had been a little more appreciative of the 

 work of other investigators, even when they differ in their conclusions from him. 

 We can excuse this if we consider this book simply as a summary of his own 

 researches, and as such can recommend it to meteorologists, especially those who 

 are interested in the theoretical side of the subject, both as a volume for reference 

 and as indicating lines along which research may profitably be pursued in the future. 



H. S. J. 



PHYSICS 



The Physical Properties of Colloidal Solutions. By E. F. Burton, B.A., 

 Ph.D. (Monographs on Physics, edited by Sir J. J. THOMSON, F.R.S., 

 and Frank Horton, D.Sc.) [Pp. vii + 200, with 18 illustrations.] (London: 

 Longmans, Green & Co., 1916. Price 6s. net.) 



This monograph contains a clearly written account of the colloidal state as far as 

 it is understood at the present time. The subjects dealt with are : preparation, 

 classification, ultra-microscopic observations, Brownian movement, optical pro- 

 perties of colloidal solutions, the size of ultra-microscopic particles, cataphoresis> 

 coagulation of colloids, stability of colloids, some practical applications of colloidal 

 solutions. The treatment is largely from the physical standpoint, considerable 

 space being devoted, for example, to the theory of the ultra-microscope. The 

 author early draws attention to the incorrectness of speaking of colloidal sub- 

 stances as a particular class. Recent work, more especially the work of von 

 Weimarn, has shown that almost any substance which exists in the solid state can 

 be produced as a colloid or as a crystalloid, it being largely a question of concen- 

 tration and the nature of the medium. Consequently one ought to speak of the 

 colloidal state just as one speaks of the liquid or gaseous states. The various 

 methods of preparing colloidal solutions are very clearly summarised. The 

 question of their possible classification is one of considerable difficulty. Indeed, 



