July 12, 19 17] 



NATURE 



-8" 

 0^0 



not possess much knowledge of the theory of 

 electricity. There is no attempt to give purely 

 electrical explanations of the principles involved ; 

 instead, the author has made free use of a few 

 well-chosen mechanical analogies, which are 

 worked out in considerable detail. 



The discussion of these mechanical vibration 

 problems, with the help of torque-time and 

 velocity-time curves, is a most attractive feature, 

 of the greatest interest to students of physics and 

 engineering. 



Part ii. deals mainly with transmitting 

 apparatus and develops the theories of the dynamo, 

 transformer, coupled circuits, spark transmitters, 

 and oscillation valves. 



TTie treatment of these, though necessarily 

 brief, is on the whole remarkably clear and 

 accurate, and is illustrated by a large number 

 •oi diagrams. 



The section, about fifty pages, devoted to oscil- 

 lation valves is very good indeed. These sensitive 

 contrivances have almost revolutionised the art of 

 wireless telegraphy during the past few years. 

 Unfortunately, there is very little quantitative 

 information given about them ; a few more num- 

 bers would have been most welcome. 



Scarcity of numerical illustrations is perhaps the 

 chief defect of the book ; the size of a piece of 

 apparatus and the numerical values of its con- 

 stants are rarely given. But this is not very 

 serious, and we can warmly recommend the 

 work as a trustworthy and stimulating intro- 

 duction to the more elaborate treatises on radio- 

 telegraphy. 



Field and Laboratory Studies of Crops: An Ele- 

 mentary Manual for Students of Agriculture. 

 By Prof. A. G. McCall. Pp. viii+133. (New 

 York : John Wiley and Sons, Inc. ; London : 

 Chapman and Hall, Ltd., 1916.) Price 35. 6d. 

 net. 



The object of this little book is to provide students 

 of school age with practical exercises in the study 

 of plant life. It is, as it were, a tAventieth-century 

 edition of the book of " Common Things " which 

 t)ored the children of earlier generations. Unlike 

 those forbidding compendiums, it seeks to lead 

 children to a study of Nature through the avenue 

 of experiment, and hence possesses a marked 

 superiority over its early prototypes. Neverthe- 

 less, it has the fundamental defect of all those 

 books which seek to evade the disciplinary grind 

 hich is the only passport into the world of 

 « ience. Thus the student is supposed to learn 

 how plants grow by marking corn roots with 

 thread or waterproof ink, and he is advised to 

 •draw an entirely erroneous conclusion, namely, 

 that sunlight is necessary for plant growth from 

 an experiment in growing plants in the dark. 

 Having performed the experiment, he is told about 

 carbohydrates and is told about photosynthesis, 

 on which things and phenomena the experiment 

 throws but little and faint light. 



If "agronomists" think that a knowledge of 

 XO. 2489, VOL. 99] 



the elements of plant physiology is useful to the 

 budding agriculturist, it would be best to let him 

 follow a simple but systematic course in that sub- 

 ject, and not to restrict him to a few odds and 

 ends of exf>eriments which serve for little else than 

 occasions for providing " morals " — conclusions 

 which may or may not follow from the experiments 

 and statistics which, though valuable enough in 

 themselves, have no legitimate relation with the 

 experiment to which they purport to refer. For 

 example (Exercise 9), the child digs up 5 lb. 

 of clover or corn, and, having determined that, 

 when exposed to the sun, it loses a considerable 

 part of its weight, is informed that a field of oats 

 uses 5^2 lb. of water for each pound of dry matter 

 produced. 



We fear that this attempt to get the child " rich 

 quick " is doomed to failure, and we do not believe 

 that even the American child will make much of a 

 success of his garden by studying Exercise 50, 

 on "Planning the Home Garden," pp. 122-24, or 

 even by purchasing the apparatus required for 

 the exercise — to wit, a 50-ft. tape and some plain 

 drawing-paper. F. K. 



Dairy Farming. By Prof. C. H. Eckles and 

 ProL G. F. Warren. Pp. xv-r309. (New 

 York :. The Macmillan Co. ; London : Macmillan 

 and Co., Ltd., 1916.) Price 55. net. 

 As was to be expected, the chapters dealing with 

 the breeds of cattle, their selection, improvement, 

 management, feeding, etc., have been written by 

 Prof. Eckles, and follow the lines of his own 

 book on that subject. He has also contributed 

 a chapter on the common ailments of cattle, and 

 one on milk and its products. Prof. Warren's 

 contribution deals with the why and wherefore 

 of dairying and dairy farming, and a great deal 

 of information is given on matters which are 

 not, as a rule, gone into very exhaustively by 

 the average teacher in this country. Neverthe- 

 less, such information is of the greatest possible 

 benefit in developing the mind of the future 

 farmer and giving him an outlook which w-ill carry 

 him above rule-of-thumb methods. 



This book is intended for teaching purposes, 



and there are questions and problems at the end 



: of each chapter, also a list of books in some cases 



• which may be read with advantage. 



I The modern farmer will find much that will 



interest him in this book, particularly in view 



of the changing conditions in our country at the 



: present time, and there seems to be every reason 



I why the value of the dairy cow as an economical 



I producer of human food should be strongly 



! pointed out to those already engaged in farm- 



I ing, as well as to those who are prospective 



i farmers. 



I It is, however, chiefly as an aid to the teacher 

 I that this book is to be strongly recommended, 

 and whilst the examples refer to American con- 

 ditions, it ought to be possible to get similar 

 data for British farms and utilise the information 

 to the same ends. 



