March 9, 1922] 



NA TURE 



303 



verte) on the same site, as in Guernsey, is another 

 litful line of thought, and no synthesis should neglect 

 de Guerin's amplifications of Dechelette's views on 

 icient incised figures and idols. 

 The movements outlined above must be taken 

 »to account by linguists who wish to find a link 

 fith archaeology, and it will probably be through 

 ie forging of that link that the great advance we 

 )k for will occur. It is possible to argue for the 

 i>read of at least some elements of the languages 

 the older philologists along the lines of distribution 

 beaker pottery, but it is quite likely that those 

 iguage elements travelled far later, with other 

 laeological correlatives, along the line determined 

 large measure by the presence of loess and the 

 )nsequent weakness of forest and swamp. One may 

 mture the statement that probably rather by such 

 tudy than by the more exclusively philological ones 

 jggested by Prof. Tyler will our knowledge of the 

 )urces of the European languages be improved, and 

 ir views as to their adoption, with modification, by 

 )ples who were not bred with them, made precise. 

 lyhow, it seems more than likely that our great 

 lihes of European languages in several cases illustrate 

 loption of a language-basis from foreigners rather 

 differentiation of languages by process of time 

 )m a single common ancestor. The references to 

 'early religion that Prof. Tyler gives seem specially 

 dangerous in the dim light of present-day doubt. 



(2) Mr. Crawford's book shows he has been trying 

 to set his thoughts in order after the trials and diffi- 

 culties of war service, and, in the midst of discursive 

 generalities, one does frequently come upon points 

 of value for the student who wants to take his archse- 

 ology regionally and to see man at each period in his 

 proper relation to the local environment of that period- 

 Fortunately, Mr. Crawford is alive to the fa(;t that the 

 environment changes with the period even after the 

 close of the Ice age. He sees that the clearing of 

 forests and the draining of swamps have made vast 

 differences to men's opportunities for movement and 

 lines of communication, and he understands the 

 difficulties of argument on these complex problems. 

 He is an impassioned eulogist of old roads and of the 

 joys of tracing them, and the beginner in prehistory 

 who is anxious to get hold of method, rather than of 

 fact, will find Mr. Crawford's book interesting and 

 profitable, though he may be left wondering why the 

 author did not omit a good deal of general talk and 

 give the student a great deal more help along his 

 ^^'ay. H. J. F. 



Rosenbusch's Petrology. 



Mikroskopische Physiographie der petr ogr aphis ch- 

 wichtigen Miner alien. By H. Rosenbusch. Band 

 I. Erste Halfte. Untersuchimgsmethoden. Fiinfte, 

 vollig umgestaltete, Auflage. By Prof. E. A. 

 Wiilfing. Lieferung I. Pp. xvi + 252. (Stuttgart: 

 E. Schweizerbart'sche Verlagsbuchhandlung (Erwin 

 Nagele), 192 1.) 16^. 



ALL who are interested in petrological studies 

 will welcome a new edition of this familiar 

 text-book, which made its first appearance nearly 

 forty years ago. Every subsequent edition has ex- 

 ceeded its predecessor in size and completeness, and 

 the fifth, to judge from this instalment of the first 

 half of the first volume, is not likely to prove an 

 exception. It is true that some of the topics dealt 

 with in eariier editions, such as the principles of 

 stereographic projection, are omitted as being now 

 sufficiently familiar to the student, but the space 

 thus saved, and more, is required for the develop- 

 ments during the seventeen years that have elapsed 

 since the previous edition was published. 



This issue is the work of Prof. E. A. Wulfing, the 

 author of the admirable account of the methods 

 employed in the microscopical examination of minerals 

 in the fourth edition of the book, and the successor 

 of Rosenbusch at Heidelberg. It has been to a large 

 extent rewritten, and there is a decided advance in 

 the clearness with which the fundamental principles 

 are explained, even if the mathematical aspect of the 

 subject is perhaps still somewhat over-emphasised in 

 places. 



The first forty pages are mainly devoted to a detailed 

 description of the most up-to-date methods of cutting, 

 grinding, and mounting thin slices of rocks. This 

 is followed by an exposition of the author's views 

 on the nature of light and an account of its properties 

 in both isotropic and anisotropic media, including 

 the phenomena of absorption and pleochroism. There 

 is also a useful section devoted to the methods of 

 producing polarised light in which the different forms 

 of prism that have been devised for the purpose are 

 described, and another to the production of mono- 

 chromatic light. 



The text is accompanied by numerous clearly 

 drawn illustrations, many of which appear for the 

 first time, and there is a handsome coloured plate 

 giving the succession of Newton's colours, the amount 

 of relative retardation corresponding to the different 

 tints, and the usual graphic representation of the 

 relation between birefringence, thickness, and relative 

 retardation. John W. Evans. 



NO. 2732, VOL. 109] 



