.3,,. SOME NEW BOOKS. 391 



stronger than the rest, gains the ascendancy ; individualism triumphs 

 over altruism, and private ownership of land is established. 



Private property was probably, in the first instance, of a strictly 

 personal character. The weapons and ornaments which a man had 

 made for himself were clearly his own belongings, and were conse- 

 quently buried with him for service in the next world. When man passed 

 from the condition of a hunter to that of a herdsman, his property 

 took the convenient form of domesticated animals. Passing, in the 

 course of ages, from this nomadic life to the settled life of an agri- 

 culturist, he acquired landed property which, as already explained, 

 would be at first of a communal character. The solidarity developed 

 in a village community led to a certain kind of altruism, and thus 

 acted as a check upon egoism. But eventually an inverse process 

 would be carried out ; the soil became parcelled out into allotments, 

 the cultivator enjoying merely the usufruct of his plot. Gradually, 

 however, the chieftains would manage to transfer this right into 

 property transmissible to their descendants, and such a practice 

 would be imitated as far as possible by the more powerful of the 

 community. 



With the historic phases of the subject, such as the development 

 of the feudal system, we have no concern in these pages ; neither do 

 we feel ac liberty to refer to the author's views on the future of the 

 right of property. For these, and many other topics, we must refer 

 to M. Letourneau's volume — a volume which will be read with much 

 interest by all who are busied with the fascinating problems of 

 evolutionary sociology. 



The Optical Indicatrix, and the Transmission of Light in Crystals. By 

 L. Fletcher, M.A., F.R.S. London : Henry Frowde, 1892. 



Every geologist who occupies himself with the study of rocks is 

 familiar with the practical determination of minerals by their optical 

 characters, and has found it necessary to acquire some knowledge of 

 Fresnei's wave-surface ; he is also probably aware that the method 

 used by Fresnel in his marvellous memoir on double refraction has 

 long been regarded as dynamically unsound, and that the nature of 

 the luminiferous ether has lately been the subject of much 

 investigation and discussion on the part of physicists. 



Now, in his quest for instruction regarding the optical characters 

 of crystals, the student is first confronted with the elastic properties 

 of the luminiferous ether, and then with the deduction of the wave- 

 surface by Fresnei's method ; and yet if he has ever endeavoured to do 

 so, he has probably failed to form any distinct conception of the 

 plane waves on which that method is based. 



A further difficulty will encumber the progress of any thoughtful 

 student when he discovers that various elastic theories of the 

 luminiferous ether have been devised, and yet that they all lead 

 to the same wave-surface. 



Mr. Fletcher's little book will not attract the attention of the 

 general reader, because, being specially intended for the student, it is 

 thrown mainly into a mathematical form ; it is, therefore, all the rnore 

 desirable to indicate the educational value of this extremely ingenious 

 treatise. 



The book is notliing less than a bold rejection of the recognised 

 methods of teaching this subject, and the substitution of a new and 

 original treatment of striking geometrical elegance which involves 



