70 4 SCIENCE PROGRESS 



a very complete discussion of these investigations, including the verification of the 

 Einstein expressions. This is followed in turn by an account of Smoluchowski's 

 theory of fluctuations, as applied to critical opalescence, and to the cause of the 

 blue colour of the sky (first explained by Lord Rayleigh), and to other phenomena. 

 Perrin then takes up the problem of radiation and the concept of the quantum, 

 particularly in relation to atomic heats and the calculation of molecular quantities. 

 One cannot but be impressed by the essential unity in aim which underlies investi- 

 gations apparently quite unconnected with one another. 



The two concluding chapters deal with the measurement of the electronic 

 charge and allied quantities which enter into the problem of the structure of atoms, 

 their genesis and destruction. There is a valuable table on page 206 giving the 

 results obtained for the Avogadro Number by the various methods employed. 

 The order of agreement is very striking. 



The book is one of extreme interest, and should be in the hands of every 

 student of science. 



W. C. M. Lewis. 



A Textbook of Elementary Chemistry. By Alexander Smith, B.Sc (Edin.), 

 Ph.D. (Munich), Professor and Head of the Department of Chemistry in 

 Columbia University. [Pp. x + 457, with 98 figures and 6 plates. First 

 British edition November 191 5.] (London : G. Bell & Sons ; New York : Tha 

 Century Co. Price 5^. net.) 



A Laboratory Outline of Elementary Chemistry. By the same Author. 

 [Pp. 152, with 22 figures. British Edition October 191 5.] (London : 

 G. Bell & Sons ; New York : The Century Co. Price 2s. net.) 

 Both of these companion elementary works have been written with the clarity 

 and interest which Prof. Smith has infused into his larger textbooks. They 

 are intended primarily for the scholar undergoing training in chemistry as a 

 general ground-work subject without the specific intention of specialising in the 

 subject. The author has consequently allowed himself more scope in the state- 

 ments of interesting collateral facts than is usually found in elementary text- 

 books. 



Such information, for instance, as the digestion of starch, fats and proteins, 

 fuel values, normal diet and food prices might seem out of place in a primary text- 

 book, but they are here so simply explained and aptly inserted that their inclusion 

 forms one of the admirable features of the present volume. Baker's bread, 

 ventilation, the world's source of energy, cellulose, mortar, colloidal suspensions, 

 magnalium, coal analyses, removal of stains, tin-plate, are a few more headings 

 chosen at random which serve to illustrate the general broadness of treatment. 



On the other hand, the textbook does not neglect the purely systematic 

 ground-work of chemistry, and the author is at pains to teach the scholar the 

 elements of correctly interpreting and formulating chemical reactions, and warns 

 him often of the pitfalls which are experienced by the majority of young students. 

 The system of separate paragraphs with heavy type headings is another 

 commendable feature, and it leaves the book free from any of the discouraging 

 feeling presented by unrelieved pages of text. Each chapter closes with a set of 

 well considered questions, and the plates have been excellently chosen. 



The practical volume contains a series of exercises dealing with the subject 

 being treated in the parallel sections of the textbook. Each has the headings, 

 Object, Apparatus and Materials, followed by descriptive directions and sugges- 



