740 



NATURE 



[June io, 1922 



and not a merit that it should be wholly free from 

 mathematical symbolism. However, it is clear that 

 M. Pacotte has read and thought deeply, and if we 

 have to confess that the results of his labours are not 

 very helpful to us, we are most ready to admit that 

 they may be very helpful to others. 



(4) Prof. Petrovitch here pursues the suggestive 

 train of thought which he has started in earlier works. 

 He begins with the familiar observation that physical 

 metaphors are used in connection with the most diverse 

 events ; thus we speak of the cooling of enthusiasm 

 or the oscillation of public opinion. Such metaphors 

 indicate that the most diverse phenomena follow 

 tendencies {allures) characterisic of mechanics. He 

 seeks accordingly to classify these tendencies into a 

 few well-marked groups and to place all phenomena 

 of all kinds whatsoever within these groups according 

 to the nature of their tendencies. These ideas (of 

 which the briefest outline must suffice here) lead 

 naturally to a scrutiny of the whole range of knowledge ; 

 M. Petrovitch's knowledge is wide and, so far as we 

 can test it, accurate ; yet he carries it easily. Ac- 

 cordingly his book will appeal to many who are not 

 immediately interested in his epistemological theses. 



We are inclined to think, however, that he overrates 

 the importance of the resemblances he studies. Thus 

 he maintains that when he has analysed any phenomenon 

 according to its tendencies and displayed its mechanical 

 analogies, he has explained the phenomenon in the 

 sense used by Kelvin when he said that to explain a 

 phenomenon was to construct a mechanical model of 

 it. Such a doctrine we think might lead to the most 

 dangerous fallacies if applied to psychology and politics ; 

 and though M. Petrovitch, confining himself to analysis 

 and not to construction, seems always to stop short 

 of the precipice, he approaches it very nearly and 

 might well lead shallow thinkers over it. 



(5) Prof. Lenard has republished in pamphlet form 

 an article which appeared in Stark's " Jahrbuch." It 

 is one more attempt to avoid the principle of relativity 

 and quantum theory, and seems, as usual, to forget 

 that it is impossible to avoid them entirely, because, 

 since they are formal theories in accord with experi- 

 ment, any other physical theory so in accord must 

 be formally in accord with them. The basic idea of 

 Prof. Lenard's theory is that every body has its private 

 ether, disturbances in a private ether being transferred 

 in some way (undefined) to a primary ether (Urather) 

 for transmission to a great distance. To those so 

 attached to ethers that the idea is attractive of an 

 infinite number of coincident ethers all moving at 

 any point with different velocities, the idea will prob- 

 ably appeal. But we confess that we see no need for 

 the Urather ; so far as we can see, private ethers would 

 NO. 2745, VOL. 109] 



suffice, together with the assumption that each observer 

 can only perceive disturbances set up in his private 

 ether. (Cf. Phil. Mag. 19. 189. 1910.) 



(6) Prof. Planck publishes here a collection of hi.s 

 semi-popular lectures and essays, partly on radiation 

 and quantum theory, partly on scientific principles. 

 All that he says here will, of course, be familiar already 

 to serious students, while for the general reader books 

 in a foreign tongue are seldom useful. No comment 

 therefore seems necessary ; to praise Prof. Planck's 

 work would be impertinent. 



(7) Finally, we come to M. Villey's very interesting 

 volume, of which the first part only is published as 

 yet. Its intention is " A ceux qui possedent deja les 

 connaissances normalement enseignees dans les traites 

 de physique elementaire, exposer les memes mati^res 

 sous une forme assez renouvelee pour stimuler leur 

 curiosite et elargir leurs points de vue " and " A ceux 

 qui veulent acquerir ces connaissances en mettant a 

 profit leur loisir, les presenter non sous I'aspect du 

 manuel pedagogique, mais sous une forme plus at- 

 trayante et de lecture plus facile." It is the second 

 object which appeals more directly to us and, we 

 think, to the author. It is impossible for a profes- 

 sional physicist to decide definitely how far the aim 

 has been achieved ; we must " try it on the dog " ; but 

 we are certain that if the author has failed, his task is 

 impossible and that the fault lies not with him but 

 with the audience he is addressing. The book is a 

 model of that simple, lucid, and logical exposition of 

 which the French language — or at least the French 

 people— alone seems capable. Every one, however 

 deeply versed in physics, will find in it something to 

 stimulate his interest and imagination. M. Villey 

 deserves the thanks of all who desire a wider diffusion 

 of scientific knowledge ; we hope that an English 

 translation will soon appear — if only somebody can 

 be found with the courage and ability to undertake it. 



N. R. C. 



Strasburger's Text-book of Botany. 



Strasburger' s Text-book of Botany. Rewritten by Dr. 

 H. Fitting, Dr. L. Jost, Dr. H. Schenck, Dr. G. 

 Karsten. Fifth English Edition Revised with the 

 Fourteenth German Edition by Prof. W. H. Lang. 

 Pp. xi + 799. (London: Macmillan and Co., Ltd., 

 1921.) 31^. ()d. net. 



THE last English edition of this well-known text- 

 book was published in i9i2,and the appearance 

 of the present volume will be welcomed by the large 

 number of students and teachers who are already 

 familiar with its many excellent features. This edition 

 appears under a new title, as " Strasburger's Text- 



