NA TURE 



473 



THURSDAY, JULY io, 1913. 



ATOMS AND MOLECULES. 



Les Monies. By Prof. Jean Perrin. Pp. xvi 

 + 296. (Paris: Felix Alcnn, 1913.) Price 3.50 

 francs. 



IN these days, when such notable and exten- 

 sive advances are being made in nearly all 

 fields ol physical research, it is extremely desir- 

 able that the results which mutually bear upon one 

 another should from time to time be collected 

 together and recorded in more or less popular 

 language. If, in addition, a leading expert can 

 be persuaded to undertake the record, the event 

 ol its publication is still more to be welcomed. 

 I'n. I. Perrin is the ideal author for a book on 

 atoms and molecules. He has virtually made 

 them visible and established their reality, and it 

 is si arcely too much to say that his work on 

 Brownian movement is the most notable of recent 

 physical researches. 



It is not always that the brilliant experimental- 

 ist is an equally brilliant exponent, but in the 

 present case it is true, and the book makes fascina- 

 ting reading. It must not be supposed that 

 Prof. Perrin has confined his attention to the 

 particular sphere of work with which his name is 

 so intimately associated. Naturally enough, the 

 details of theory and experiment are treated more 

 completely in those chapters which are mainly 

 records of the author's work. But the book as 

 a whole has a broad outlook, and the atomic theory- 

 is considered from many different points of view 

 and in the light of all the recent developments of 

 the subject. 



The first two chapters are devoted to a historical 

 survey of the chemical and physical sides of the 

 atomic theory and the early methods of estima- 

 ting the size and number of the atoms. Then 

 follow the chapters' on Brownian movement pre- 

 vious!}' referred to, in which the author shows 

 how it is possible by four distinct methods to 

 measure the atoms, with remarkably consistent 

 results. The later chapters on opalescence, the 

 quantum theory, and radio-activity have the same 

 end in view, and in conclusion the author com- 

 piles the values obtained by thirteen different 

 methods for Avogadro's number. A quotation 

 from the author is the best comment on these note- 

 worthy results. 



"On est saisi d'admiration devant le miracle 

 de concordances aussi precises a partir de pheno- 

 menes si diffeVentes. D'abord qu'on retrouve la 

 m£me grandeur, pour chacune des methodes, en 

 variant autant que possible les conditions de son 

 NO. 2280. VOX-. Ql"l 



application, puisque les nombres ainsi definis sans 

 ambigui'te par tant de methodes coincident, cela 

 donne a la realite moleculaire une vraisemblance 

 bien voisine de 1 1 certitude." 



Chapter vii. is one of special interest. In it 

 the author deals with the determination of e, the 

 atom of electricity, by the method of falling drops. 

 He takes the view that the accuracy claimed by 

 Millikan for his measurements is not justified on 

 account of the magnitude of the correction to 

 Stokes's law which has to be applied, and produces 

 evidence which he regards as removing the well- 

 known discrepancy between his own and Milli- 

 kan's estimates. It remains to be seen whether 

 Prof. Millikan assents to this view. 



THE CULT OF Till: I III SDERSTONE. 

 The Thunder-weapon in Religion ami Folklore. A. 

 Study in Comparative Archaeology. By Dr. 

 Chr. Blinkenberg. Pp. xii+122. (Cambridge 

 University Press, 1911.) Price 55. net. 



THIS little book forms an interesting addition 

 to the archaeological and ethnological series 

 for which anthropologists are indebted to the 

 Cambridge University Press. The author shows 

 much erudition and industry in his search for 

 specimens illustrating the cult of thunderstones 

 which are preserved in the museums of England 

 and the Continent. He has explored the volu- 

 minous literature of the subject, and he has added 

 a series of illustrations which add much to the 

 scientific value of the monograph. 



His theory assumes that the cult of the thunder- 

 stone was an element of human culture which, at 

 an early date, that is to say, in the Stone age, 

 was gradually spread from people to people over 

 a great part of the world : that it appears in the 

 early ^Egean culture ; that the ideas of tabu or 

 sanctity attaching to these stones indicate the rise 

 of the belief from primitive conceptions of nature 

 and religion. In other words, he supposes that 

 as early as the Stone age men compared the 

 effects of the lightning-stroke to that of the axe 

 wielded by primitive man, and that this explana- 

 tion accounts for the superstition in most parts 

 of the world. 



Various difficulties, of which the author is 

 aware, prevent the acceptance of this theory of 

 origins. The most important is that the super- 

 stition has not been traced among those races 

 which possessed a Stone age culture down to 

 modern times — the peoples of Australia, Oceania, 

 and North America — while in South America, to 

 say the least, the evidence is weak. On the other 

 hand, it is common in Africa, among races which 



