190 



confirmation on a practical scale of the indirect fertilising effect 

 of partial sterilisation in killing off the protozoa which normally 

 keep down the numbers of those bacteria that prepare nitrogen- 

 food for plants. 



XVIII. 



Theories of fertiliser action. Experiments with fertilizers. 

 Experimental fields. General considerations on field expe- 

 rimentation. The effect of manures on soils and on vege- 

 tation. Influence of manures on different crops. Manuring 

 in regard to climate. 



A. D. HALL. Fertilisers and Manures. J. Murray, Lon 

 don, 1909. Pp. xv-384 and illustr. 9). 



" If this book, says the author, is to have any justification for 

 its existence, it will be by helping men to a greater skill and 

 knowledge in the use of their fertilisers and manures. There is no 

 lack of books which give ah account of the origin and composition 

 of fertilisers; my object is rather to make the ?eader understand 

 their mode of action and their relation to particular crops and soils. 

 For it is only by understanding the why and the how that a farmer 

 can properly adjust his manures to his soil and his style of farming; 

 he must to some extent reason the scheme out for himself, he can- 

 not simply be told." 



" The object, then, of the scientific man should be to lay down 

 principles which the practical man in his turn must learri to apply 

 to his own conditions; success is only possible when he too does 

 some thinking. Further more, the object of experiments should be 

 to provide knowledge that can be thus applied to other conditions, 

 and an experiment is practical just in so far as it carries out its 

 avowed object, which is to lead men into a sound and fruitful way 

 of thinking on the question at issue. 



" It is in this respect the elucidation of general principles 

 that the Rothamsted experiments have proved so exceedingly va- 

 luable ; though initially laid out to test certain definite questions 



