32 



NATURE 



[March io, 1910 



"The interest in the teaching of agriculture," con- 

 tinues the author, " is but a part of a niuch larger 

 question — the movement for teaching by means of 

 things that have come within the student's experience. 

 The underlying reason why such teaching is desirable 

 is because it brings the schools in touch with the 

 home life — the daily life of the community. A large 

 part of our teaching has had no relation whatever to 

 our daily life." 



Thus the author justifies the introduction 

 of agriculture into a high school. The sub- 

 ject is undeniably interesting to elder scholars whether 

 they propose going in for farming or not, but the 

 author goes further, and maintains that it is of real 

 educational value and can be presented in such a way 

 as to train the student to think. Few people would 

 dispute these views, but we have had to wait until 

 now for a little handbook in which they are logically 

 carried out. 



The book is not, of course, intended for elementary 

 schools. The author presupposes some knowledge of 

 chemistry and botany, and makes no attempt to gloss 

 over difficulties. It is doubtful whether a scholar 

 could study the subject profitably until he is some 

 sixteen years of age. The author begins with the 

 principles underlying the improvements of plants and 

 animals by crossing and by selection. Mendel's law 

 and its applications are dealt with at length, and 

 mutation forms are also discussed. In illustration 

 of the improvement effected it is show^n that the per- 

 centage of sugar in the sugar beet has increased from 

 8 to 18 per cent, or more, whilst maize, cotton and 

 other crops have undergone no less change. The 

 propagation of plants forms the subject of the next 

 chapter. Root stocks, tubers, cuttings, grafting, 

 budding, are described in some well-illustrated pages, 

 and then we pass to the consideration of seeds and 

 germination tests. The student is thus led to the 

 study of the food required by the young plant ; he 

 finds that at first it comes from the seed, afterwards 

 from the air and the soil. A brief sketch is given of 

 the processes going on within the plant, the manufac- 

 ture of plant food, and so on. The soil is next con- 

 sidered; it is shown to consist of small rock particles, 

 soil water, soil air, decaying organic matter, and 

 living organisms, all of which are dealt with in some 

 detail. As usual in American books great stress is 

 laid on the importance of soil water. The reason is 

 very obvious; two-fifths of the United States is too 

 dry to raise good crops without irrigation, and the 

 Government is building large reservoirs for storing 

 irrigation water. Further, dry farming is practised 

 there to a greater extent than anywhere else as yet. 

 On the other hand, on the Atlantic coast the water 

 supply is sometimes too great and a good deal of the 

 land requires draining. 



The author discusses at some length the methods 

 for maintaining the fertility of the land. Soils have 

 become productive by lying for ages in prairie or 

 forest condition whilst organic matter has gradually 

 accumulated until some sort of equilibrium is attained. 

 With the advent of man the equilibrium is upset, the 

 prairie is broken up, grain is grown for many years, 

 and the wastage, which in any case would 

 be considerable, is increased bv the common 

 NO. 2106, VOL. 83] 



habit of burning the straw of the crops. 

 Only in old, long-settled countries is the full 

 value of farmyard manure appreciated. "Very 

 few farmers in any part of America," says the author, 

 " have yet learned to handle manure without losing 

 one-half of its value." Among the causes of decreased 

 productivity, erosion by wind or water is considered 

 the worst, but it may be prevented by keeping the 

 soil in crop as much as possible. Exhaustion of the 

 humus supply is, however, regarded as the funda- 

 mental cause for the decrease in crop yields. Methods 

 of restoring the fertility of the soil by means of 

 manures, green crops, and animal excretions are 

 described. Then follow some interesting chapters on 

 the various crops— maize, cotton, wheat, timber and 

 so on — their economic importance, their methods of 

 cultivation, and the pests to which they are liable. 

 Finally, there is a discussion on the feeding of 

 animals. 



The treatment quite justifies the author's claim that 

 agriculture is a suitable subject for training the mind. 

 The book is conceived in a scientific spirit, and 

 executed with great skill. It is just the book for the 

 young agricultural student, or, indeed, for any young 

 student. All the illustrations are, naturally, American, 

 but the teacher on this side will find it very useful in 

 making up his course, although he will probably wish 

 that an equally good book written from an English 

 standpoint was available. 



ELECTRONIC THEORY OF MATTER. 

 La Radio attivita. A. Battelli, A. Occhialini, S. 



Chella. Pp. xxxii+xii + 438, Atti della fondazione 



scientifica Cagnola dalla sua istituzione in Pot. 



Vol. xxii. (Milano, 1909.) 

 WO of the most noticeable features of Continental 

 publications of a scientific character are, first, 

 fhe number written in a semi-scientific manner for 

 (Kjpular consumption, and, secondly, the variety 

 dealing with special branches of chemistry or physics 

 in a manner capable of being readily followed by 

 men of science interested chiefly in other branches of 

 these subjects. The present volume is an excellent 

 example of the second class. The first part consists 

 of reports on essays concerned with different subjects, 

 and is followed by the work of Prof. Battelli and his 

 coadjutors, to whom a prize of 2500 lire and a medal 

 were awarded for their memoir on "The Discovery of 

 Radio-activity and its Influence on Physical and 

 Chemical Theory." 



In this book of 438 pages the chief facts of radio- 

 activity are set forth in a most interesting and lucid 

 style, and their bearing on chemical affinity, the 

 electronic theory of matter, and the periodic law is 

 discussed in a manner equally able. The standard 

 books on conduction in gases and radio-activity usually 

 contain too much detail, except for experts in these 

 branches of physics ; the present authors do not pro- 

 fess to give a full account of the facts, but only of 

 those that are necessary to show the development of 

 recent theory. Great praise is due, not only for the 

 clearness with which, these facts are dealt, but also 

 for the skilful choice of material from a large mass 



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