April i, 1920] 



NATURE 



131 



farmer will derive inspiration, together with a 

 useful fund of information, from this book, which 

 is written with the clearness of exposition and 

 forcible reasoning- which are so characteristic of 

 all Dr. Russell's writings. The opportunity of a 

 new edition has been taken to embody in the 

 section on fertilisers and manures the new 

 materials and the new points of view which the 

 difficulties of war-time have introduced into British 

 agriculture, whereby the book equips the student 

 with a comprehensive epitome of the resources 

 now at his disposal. C. C. 



Our Bookshelf. 



Mathematics for Collegiate Students of Agriculture 

 and General Science. By Prof. A. M. Kenyon 

 and Prof. W. V. Lovitt. Revised edition. 

 Pp. vii + 337. (New York : The Macmillan Co. ; 

 London : Macmillan and Co., Ltd., 1918.) Price 

 los. 6d. net. 

 "This book is designed as a text in freshman 

 mathematics for students specialising in agricul- 

 ture, biology, chemistry, and physics in colleges 

 and technical schools " (p. v). Whatever may be 

 the needs of the American student, the book would 

 scarcely be of use in this country. Originality is 

 not expected in a small book designed to be "the 

 entire mathematical equipment of some students " 

 (p. v), but the chapter on statics would surely be 

 much improved if it contained some account of 

 simple machines. The section headed "Mendel's 

 Law " on p. 282 is defective and misleading ; 

 witness the following exercises (p. 284) : " A 

 farmer buys two different kinds of thoroughbred 

 chickens, but allows them to mix freely. How 

 many different kinds of chickens will he have at 

 the end of (a) the first, (b) the second, (c) the third 

 year of hatching? Ans. (a) 3, (b) 5, (c) 9." 



R. A. Fisher. 



The Elements of Descriptive Astronomy. By 

 E. O. Tancock. Second edition, revised, with 

 additional matter on practical work for begin- 

 ners with small instruments. Pp. 158. (Oxford : 

 At the Clarendon Press, 1919.) Price 35. net. 

 Mr. Tancock is the secretary of the committee 

 appointed by the British Astronomical Association 

 for the purpose of encouraging the teaching 

 of astronomy in schools. This book is based 

 on courses of lessons which he gave to junior 

 forms. A large portion of it is descriptive 

 of the aspect and nature of the various 

 orbs, of which excellent photographs and 

 drawings are reproduced. The remainder is 

 devoted to explaining the celestial motions, which 

 is done in a lucid manner. Instructions are given 

 for making a model of the celestial sphere on the 

 surface of a spherical flask that is half filled with 

 some dark fluid. A useful series of questions and 

 exercises is appended, also a set of passages relat- 

 ing to astronomy, selected from English literature, 

 on which explanation or criticism is invited. 

 NO. 2631, VOL. 105] 



An erratum occurs on p. 55. The time of 

 revolution of Saturn's outer ring should be 

 137 hours, not 137. 



Vital Statistics: An Introduction to the Science 

 of Demography. By Prof. George Chandler 

 Whipple. Pp. xii-t-517. (New York: John 

 Wiley and Sons, Inc. ; London : Chapman and 

 Hall, Ltd., 1919.) Price 185. 6d. net. 

 This manual is intended for American public 

 health officials who, in the author's words, have 

 forgotten most of their arithmetic- — not to mention 

 algebra. A good deal of space is consequently 

 devoted to the details of tabulation and the making 

 of diagrams. The census and the statistics of 

 births, marriages, and deaths are fully treated. 

 The absence of uniform laws in the different States 

 of the Union, and the mixed character of the 

 population, are sources of many pitfalls for the 

 student. General rates are of little value in deal- 

 ing with a population of native-born whites, 

 foreign-born whites, and negroes, and the author 

 duly emphasises the need for care in such cases. 

 The more theoretical parts of the book touch on 

 frequency curves, correlation, and the structure 

 of a life table. In the chapter on correlation, a 

 coefficient 054 is described as low, and cited 

 as an example of the use of the coefficient as " an 

 admirable weapon for exploding false theories." 

 A public health official would need more technical 

 knowledge than is provided in this book to justify 

 him in rejecting a coefficient of this magnitude. 



Insect Life on Sewage Filters. By Dr. W. H. 



Parkinson and H. D. Bell. Pp. viii-f64. 



(London: Sanitary Publishing Co., Ltd., 1919.) 



Price 3s. 6d. net. 

 The title of this little book is rather misleading. 

 The original matter deals almost entirely with 

 one species of insect, Achorutes viaticus, in rela- 

 tion to the efficiency of the sewage filters where 

 it is very frequently found in large numbers. The 

 authors seek to prove that Achorutes attack and 

 consume the colloidal matter and fungoid growths 

 which often choke the upper layers of the filters, 

 and in this way enable a larger volume of sewage 

 to be purified than is possible when these insects 

 are not present. Experiments were made with 

 two filters ; in one precautions were taken to 

 exclude Achorutes ; in the other the insects were 

 encouraged to develop. Analyses of the effluents 

 produced by these filters showed that where 

 Achorutes was absent the purification effected was 

 less than in the other filter, but when the insects 

 were added to the first filter nitrification improved 

 at once. Although the authors' conclusion seems 

 to be justified, their interesting experiment is 

 scarcely worthy of publication in book form. The 

 biological details appear to be mostly from Haig 

 Johnson's work on the subject. 



The Transmutation of Bacteria. By Dr. S. 



Gurney-Dixon. Pp. xviii -1-179. (Cambridge: 



At the University Press, 1919.) Price 105. net. 



This small book deals with certain variations, 



morphological and physiological, which are 



