March 20, 1919] 



NATURE 



43 



OUR BOOKSHELF. 



Tables of Refractive Indices. \ ol. i. " Essential 

 Oils." Compiled by R. Kanthack. Edited by 

 Dr. J. N. Goldsmith. Pp. 148. (London: 

 Adam Hilger, Ltd., 1918.) Price 155. net. 

 This volume is the first of a series, in which it 

 is proposed to publish the values of the refractive 

 indices appertaining^ to various technical products. 

 Used with discretion, the refractive index is a 

 property which will often give valuable informa- 

 tion as to the purity of a liquid, and it is a pro- 

 perty which is readily determined. Another ad- 

 vantage is that, given a suitable refractometer, 

 a very small quantity of the substance suffices for 

 the determination. In examining essential oils 

 the value of the refractive index is a very useful 

 datum, and it is convenient to have the numerous 

 recorded observations, hitherto scattered over the 

 literature, selected, scrutinised, and brought to- 

 gether in a handy form such as that of the book 

 before us. 



The data which Mr. Kanthack has collected are 

 arranged in tables occupying the right-hand pages 

 of the book, the opposite pages being left blank 

 for notes. In the first column of the table are the 

 names of the oils in alphabetical order, with their 

 botanical origin, and often their geographical 

 source also. Then follows the refractive index, 

 the temperature of the observation being given in 

 every case. With respect to this last point, 

 abstractors of chemical literature would do well 

 to note the author's remarks upon the futility of 

 stating a refractive index unless the temperature 

 of the observation is also given. Finally, there 

 is a reference to the authority, and this Will be 

 found an important feature, because there are 

 some two hundred and eighty of these references, 

 and they form a good guide to the literature of 

 the subject. In fact, some of the index-values, 

 which would otherwise be redundant, have been 

 purposely utilised for introducing references to 

 important work or special information. Chemists 

 who are concerned with the examination of 

 essential oils will find the book decidedly helpful. 



An Introduction to the Study of Biological 

 Chemistry. By Prof. S. B. Schryver. (Modern 

 Outlook Series.) Pp. 340. (London : T. C. and 

 E. C. Jack, Ltd., n.d.) Price 65. net. 

 Pur author is to be congratulated on a very useful 

 addition to chemical literature. The special 

 feature of the book is a careful choice of examples 

 which are of peculiar interest to students of bio- 

 logical chemistry. The first 178 pages are devoted 

 to a description of general chemical methods, and 

 to a study of the chief groups of organic sub- 

 stances ; and, while no attempt has been made to 

 give full details of the properties of the individual 

 com{X)unds, a succinct account has been given of 

 the relationships between the various groups. 



A specially good feature is the inclusion of, and 

 the prominence given to, synthetic methods, and 

 careful accounts are given of Grignard's reaction, 

 Friedel and Crafts' reaction, the malonic ester 

 reaction, Kiliani's reaction, and Sandmeyer's rc- 

 NO. 2577, VOL. 103] 



action, as illustrative of general synthetic methods. 

 A very useful chapter deals with optical activity 

 and the chemistry ot stereoisomerism. The treat- 

 ment of the aromatic substances is brief, but 

 sufficient for the purposes for which the book is 

 intended. The remainder of the book is devoted 

 to the study of the chief chemical constituents of 

 the animal body, and the chemistry of the fats 

 and carbohydrates is given in more detail than is 

 usual outside special monographs. To the student 

 of bio-chemistry the constitution and properties 

 of the proteins are questions of fundamental im- 

 portance, and have been fully treated. The purely 

 chemical part of the book is completed by special 

 chapters on the methods employed for the investi- 

 gation of the chemical changes within the animal 

 organism, and on the chemical processes in plants. 

 In these chapters the main features of enzyme, 

 action are dealt with, and the nature of the 

 changes which occur during the intermediate meta- 

 bolism of the foodstuffs is discussed. 



In conjunction (as the author suggests) with 

 suitable practical exercises worked in the labora- 

 tory, the book should prove very useful, and forms 

 an excellent basis for the preliminary training of 

 medical students or of agricultural students in 

 those lines of thought which are of service to 

 them. The book is tersely and continuously 

 written, each chapter carefully summarised, and 

 an efficient index is provided. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for 

 opinions expressed by his correspondents. Neither 

 can he undertake to return, or to correspond with 

 the writers of, rejected manuscripts intended for 

 this or any other part of Nature. No notice is 

 taken of anonymous communications.] 



Globular Clusters, Cepheid Variables, and Radiation. 



I WAS much interested to see in the letter bv Dr. 

 Harlow Shapiey bearing the above title (Nature, 

 March 13, p. 25) that new astronomical evidence 

 makes it necessary again to challenge the almost uni- 

 versal assumption that radiation is uniformly propa- 

 gated in all directions through free space. ' I have 

 long felt that this unjustifiable assumption was at 

 the bottom of the difficulty of accounting for the 

 maintenance of solar and cosmical energy even over 

 the periods of time demanded by geological history, 

 and I have often thought that, even though no actual 

 crucial test is possible, experimental evidence on such 

 an important question ought to be attempted. In a 

 review of Dr. N. R. Campbell's "Modern Electrical 

 Theory" (Nature, vol. xcii., p. 339, 1913) I pointed 

 out that experiment and observation justify only the 

 conclusion that radiation is propagated between por- 

 tions of space occupied by matter, and that elsewhere 

 it may not be propagated "at all. The frank confession 

 of complete ignorance on this, the simplest first ques- 

 tion as to the nature of radiation in its cosmical 

 aspect, would put an entirely difTeront complexion on 

 the doubtful generalisations from laboratory science 

 to cosmology. .As Dr. Shapiey calculates with regard 

 to solar radiation, the ordinary .issumption demands a 

 loss of energy one hundred million times greater than 

 experimental evidence- justifies. 



Frederick Soddy. 



