244 



NATURE 



[August 24, 191 1 



forest owners. Its value at present is great, and it 

 will become greater in direct proportion to the spread 

 of scientific forestry training and the extended affores- 

 tation of suitable lands in this country. 



A. W. B. 



THE MECHANICS OF THE SOCIAL BODY. 

 Mdcaniquc Sociale. By Prof. Sp. C. Haret. Pp. 



iv + 256. (Paris: Gauthier-Villars ; Bucarest : Ch. 



Gobi, 1910.) Price 5 francs. 



THIS volume represents an attempt by Prof. Haret 

 to apply the laws and methods of mechanics to 

 the study of sociology. The condition of an indi- 

 vidual at any point of time, he argues, may be con- 

 ceived as indicated (at least, in its principal aspects) 

 by the magnitudes of three different factors — his 

 economic possessions, his intellectual state, and his 

 moral state. Supposing these three quantities to be 

 measurable, the condition of the given individual at 

 the given time can be represented by the coordinates 

 of a point P, with reference to three rectangular axes 

 OX, OY, OZ, which define his position in the " social 

 space." If these coordinates do not change, the indi- 

 vidual is in a state of "social rest"; when they vary, 

 he is in a state of "social movement." Any cause 

 which may produce or vary a social movement is 

 termed a "social force," and any such force may be 

 represented by a vector in the social space. Two indi- 

 viduals are said to possess the same " social mass " 

 when the same social force, applied for the same 

 time, produces the same movement. With such defini- 

 tions, it is argued, all the ordinary laws of statics 

 and dynamics apply. 



That the idea is a novel one, possessing some 

 attractiveness, we are willing to concede. Thescheme 

 of coordinates chosen also emphasises the fact, occa- 

 sionally forgotten in some statistical investigations, 

 that economic, moral, and intellectual changes are 

 not (to use the common phrase) on the same plant-, 

 and index-numbers which measure changes in such 

 diverse quantities should not be averaged together. 

 But that the laws of mechanics apply to a system of 

 material points representing, in the way described, 

 the condition of a given population, does not seem to 

 be proved. 



The very difficulty that would surely occur to almost 

 any reader at the commencement is ignored, and this, 

 it seems to the reviewer, is the source of all subse- 

 quent difficulties. The three axes chosen do not repre- 

 sent quantities of the same kind or dimensions, but 

 quantities quite different in kind. The mere repre- 

 sentation of movement in the "social space," the 

 magnitudes and directions of velocities and accelera- 

 tions, will .ill depend on the three arbitrary scales 

 chosen. Forces parallel to the three axe- do not 

 diller merely in direction but in kind : we cannot 

 speak of forces which are equal in magnitudi 



n nt in direction until the three scales are defined. 

 Iliit the ratio of the masses of two individuals is 

 not the same for all forces is admitted: for a given 

 force in one direction the acceleration produced in A 

 may bi greatei than thai produced in B; for a 

 in .another direction the contrary may be the 

 NO. 2l82, VOL. 87] 



The "economic," "moral," and "intellectual masses" 

 of the individual are, in fact, like "economic," 

 "moral," and "intellectual forces," totally different 

 things. Prof. Haret proposes to evade the difficulty 

 by regarding the forces as varying instead of the 

 masses, but this is surely inadmissible. If A and 

 B move, say, with the same accelerations when 

 subjected to the same economic force, but with different 

 accelerations when subjected to the same moral force, 

 it is impossible to say that one and the same force is, 

 in the latter case, different for the two individuals 

 merely in order to avoid admitting that their " masses " 

 are different. 



It is with regret that the reviewer finds himself 

 unable to accept the author's thesis, for undeniably 

 it possesses a certain picturesque suggestiveness. 

 Economic forces, for example, are often of a more or 

 less periodic character, and seem to be accompanied 

 by moral forces which are also periodic. If these got 

 a quarter of a period out of phase with each other, 

 the social body would start revolving round its intel- 

 lectual axis . . . What would happen? G. U. Y. 



THE GUM-TREES OF AUSTRALIA. 

 A Critical Revision of the Genus Eucalyptus. By 

 J. H. Maiden. Vol ii., part i.-part xi., of the com- 

 plete work. Pp. iv + 59 + iv plates. Vol. ii., part ii- 

 part xii of the complete work. Pp. iii + 6i-ioo + iv 

 plates. Published by authority of the Government 

 of the State of New South Wales. (Sydney : W. A. 

 Gullick, Government Printer, 19 10.) Price 2s. 6d. 

 each part. 

 ""T^HE first part of this comprehensive work was 

 A issued in 1903, and it is wholly devoted to the 

 description and illustration of Eucalyptus pilularis. 

 Parts two and three appeared in the same year, each 

 dealing with only one species, E. obliqua and E. 

 calycogona respectively. When reviewing those early 

 parts, each of which contains four plates of figures, 

 we ventured to suggest that Mr. Maiden had com- 

 menced with a fullness of detail that might imperil 

 the completion of the work, considering that the 

 genus comprises many more than a hundred species. 

 Two species, E. incrassata and E. foccunda, are de- 

 scribed in the fourth part (1904), and illustrated by 

 no fewer than twelve plates. At this rate the prob- 

 abilities of completion seemed to be exceedingly re- 

 mote, and the author apparently realised the fact, for 

 succeeding parts have included successively a greater 

 number of species ; parts one and two of the second 

 volume containing ten species each, illustrated by 

 four plates. 



It is almost superfluous to mention that the genus 

 Eucalyptus is the most important commercially in the 

 vegetation of Australia, and its elucidation is corre- 

 spondingly desirable. Some of the species are very 

 abundant and widely dispersed, whilst others are very 

 ran and local, and consequently liable to extinction. 

 At least two other botanists — Bentham and Mueller 

 have dealt with the whole genus before Maiden 

 took up the work, and Mueller also possessed field 

 knowledge. But one generation of botanists by no 

 means mastered all the details of classification of this 



