Decembeb 25, 190S] 



SCIENCE 



927 



potent in securing the interest and attention 

 of students, who instinctively recognize the 

 diSerence between the teacher who merely 

 transmits what others have said and done, and 

 the one who as an active investigator has in- 

 creased the store of knowledge. 



Snyder's important researches on humus 

 and the nitrogen of soils are well summarized 

 and render this portion of the book especially 

 valuable and complete, in showing quantita- 

 tively the increase and decrease of nitrogen 

 under different methods of culture, largely on 

 the basis of investigations made by the author 

 himself. The entire subject of soil fertility 

 and fertilization is so comprehensively yet 

 briefly treated, that while nothing really 

 essential is omitted, one is forcibly struck with 

 the immensity of the field, and the total in- 

 adequacy of the time and preparation usually 

 bestowed upon it even by those who are at- 

 tempting to prepare themselves to be active 

 •workers in experiment stations. The one- 

 sidedness and narrowness of the ordinary 

 course of preparation for such activity is 

 strongly emphasized by what, for brevity's 

 sake, Snyder has to leave unsaid in this ex- 

 cellent book. But the practical applications 

 of the facts and principles given are so well 

 interwoven with the latter that " a peg is 

 struck " in connection with each, in the mind 

 of the reader or student, and wiU strike the 

 practical farmer as well. To both classes of 

 readers, and more especially to teachers of 

 agriculture, this volume will be most welcome 

 and useful. 



Intended as the book is mostly for the tem- 

 perate humid region, its omissions as concerns 

 the arid region and the tropics are perhaps 

 not a fair subject for criticism. The index 

 is somewhat scantier than it should be for 

 convenience of reference, when such subjects 

 as alluvium, subsoil, leaching of soils, root 

 penetration and others of similar importance, 

 can not be conveniently located by its aid. 



E. W. HiLGARD 



The New Physics and Its Evolution. By 

 LuciEN PoiNCARE. Authorized translation. 

 Pp. 344. New York, D. Appleton & Co. 

 1908. 



Professor Poincare says in his preface: 

 It has occurred to me that it might be useful 

 to write a book which, while avoiding too great 

 insistence on purely technical details, should try 

 to make known the general results at which 

 physicists have lately arrived, and to indicate the 

 significance of the recent speculations on the con- 

 stitution of matter and of the recent discussion 

 of first principles. 



One of the most interesting things to the 

 physicist in this book is the author's insist- 

 ence on the atomic theory as a fundamental 

 principle which he would place on a par with 

 the principle of the conservation of energy 

 and the principle of Carnot and Clausius (the 

 second law of thermodynamics). Indeed, it 

 may be said, using the author's words, that 

 the atomistic synthesis, but yesterday so de- 

 cried, is to-day triumphant. 



Professor Poincare is one of the leading 

 exponents of the view, which has always been 

 held by the experimentalist, that the truth of 

 a theory is solely its availability for use, and 

 the value of Professor Poincare's recent books 

 lies to a great extent in the manner in which 

 he sets this view before that great body of 

 insistent and shameless theorists, the general 

 public. 



The scope of Professor Poincare's book is 

 sufficiently indicated by the above extract 

 from his preface, and its quality is sufficiently 

 indicated by the statement that it has an in- 

 terest to the physicist and a value to the 

 general reader. Let us, therefore, return to 

 the paradoxical statement concerning the 

 general public, our persistent and contented 

 theorists, and let us illustrate by taking an 

 example which every one should be able to 

 appreciate. It is very well for a sailor, per- 

 ceiving that the wind blows, to set his sails 

 accordingly; and he usually knows well how 

 to do it. But a sailor's grandson who sets 

 himself to studying the wind, let him be care- 

 ful how he uses the idea which pervades this 

 simple perception. 



Even the apparently steady flow of a great river 

 is an endlessly intricate combination of boiling 

 and whirling motion; and the jet of spray from 



