»42 



NAT URL 



[November 28. rgiS 



vibratory movements, and of wave motion. 



Chap. \ii. (lrals briefly with ihc subject of acous- 

 tics, and includes a detailed description ol the 

 anatomy of the ear, with excellenl diagrams after 

 \. Pizon. Then follows a length) section devoted 



lo physical optics, in which the subjects of 

 interference, diffraction; and polarisation are dis- 

 cussed in a masterly manner, cine of the valuable 

 features of this portion of the work being the 

 number of problems winked out in detail with 

 numerical illustrations. In dealing with the 

 passage ol' polarised lighl through crystalline 

 plates extensive use is made ol the geometrical 

 construction devised by Poincare, in which tin 

 characteristics ol" the elliptic-ally polarised light 

 ire represented by the position of a point on the 

 surface of a sphere. 



The damped oscillations of certain material 

 systems, such as moving-coil galvanometers, are 

 considered in chap. x\. At first sight the chapter 



on thermionic apparatus seems somewhat out of 

 place, but this impression is removed when il is 

 realised how important a part thermionic valves 

 and amplifiers play in connection with electric 

 oscillations and wireless telegraphy and tele- 

 phonv. Recent improvements in these depart- 

 ments of applied electricity are described in most 

 interesting fashion. The remaining chapters deal 

 with electro-optics and optical effects due to 

 motion, the volume closing with a brief review 

 of the principle of relativity. 



Special interest attaches to this volume through 

 the circumstances in which it has been produced. 

 In an introductory statement M. Ollivier says : 

 "Ce n'est pas sans une profonde emotion que 

 nous publions ces lecons professees a Lille avant 

 la guerre. Car aux souvenirs heureux qu'elles 

 evoquent pour nous, au rappel d'un temps oil 

 notre University etait grande et florissante, 

 s'ajoute en un conlraste dechirant la longue et 

 cruelle vision des malheurs qui sont venus. Ce 

 n'est pas a nous qu'il appartient de decrire les 

 souffrances infinies de la ville martyrisee. Mais 

 nous ne voulons pas signer ce livre sans adresser 

 un hommage a nos collegues et a nos eleves 

 morts. " 



(2 and ;,) Two useful books for beginners are 

 provided by Mr. Risdon Palmer, who is familiar 

 with the difficulties of both student and teacher. 

 In the study of electricity the analytic method is 

 employed. The first experiments to be performed 

 involve the use ol accumulators, glow-lamps, ad- 

 justable resistances, voltmeters and ammeters. 

 Even if the treatment is not strictly logical, the 

 student at once acquires some familiarity with 

 the notions oi electromotive force, resistance, and 

 current. In magnetism the idea of pole strength 

 is based on the use of a simple form of magnetic 

 balance, and the experiments are supplemented by 

 illustrative examples and arithmetical questions. 

 Considerable emphasis is rightly laid on the ex- 

 pression of results in the appropriate units, the 

 realisation of the magnitude of the quantities 

 involved, and graphical representations. 



H. S. An 1 v. 

 NO. 2561, VOL. I02] 



PRACTICAL FORESTRY. 



Forestry Work. By \V. II. Whellens. Pp. 236. 

 (London: T. Fisher Lnwin, Lid., 1918.) Price 

 .S.s. en/, net. 



TI1L author of this book is a working forester, 

 who has bad much experience while in 

 Chargl of large wooded estates in England and 

 Si. .il. md. lie tries to explain in simple larigu 

 the actual operations which are usually 1.1 



out on such estates, and in this is Fairly successful. 

 The book can be recommended as a useful on< 

 lor the forestry apprentice, and will be found 

 serviceable in giving instruction to disbanded 

 soldiers and to women who are now taking shori 

 courses in nursery work, measuring timber, etc., 



at various centres. There is nothing novel in tin- 

 book, which is simply a straightforward account 

 of ordinary British forestry practice. Whether this 

 practice requires amendment or improvement is 

 another matter. Hitherto, on private woodland 

 cslates, methods have been in vogue which are 

 not strictly economical. In the future money will 

 be- scarce, and efforts must be made either to 

 invent cheaper methods or 10 import such from 

 foreign countries, like the United States, where 

 of tate ingenious inventions have been devised, 

 which save labour materially in the planting and 

 in the felling of trees. 



Mr. Whellens's first chapiter deals mainly with 

 nursery work, and contains much that is valuable 

 and well put; but no mention is made of the trans- 

 planting lath or of the method employed at 

 Brocklesby and Abbeyleix, by which young trees 

 arc ploughed out of the nursery lines instead of 

 being lifted; yet these are excellent labour-saving 

 devices. The chapter on the preparation of the 

 ground for planting, on draining, and on fencing 

 is well done. Sowing and planting are next dealt 

 with. The chapter on tending plantations is un- 

 satisfactory, the difficult subject of thinning being 

 too briefly treated, while much space is given to 

 pruning, an unnecessary and expensive operation 

 in most cases. Felling- timber is rather summarily 

 disposed of, and nothing is said about clearing 

 the area after felling. The space devoted to the 

 measurement of timber is quite inadequate, and 

 requires considerable enlargement to make the 

 subject intelligible to workmen. 'file chapter on 

 insect and fungoid enemns is without illustrations, 

 and the descriptions are too short. The appendix 

 is a collection of useful tables. 



DEVELOPMENTS <»/•' THE THEORY Of 



RELATIVITY. 

 The Theory of the Relativity of Motion. Bj 

 R. C. Tolman. Pp. ix + 225. (Berkeley: 

 University of California Press, 11)17.) 



THE author of this book takes much lor 

 granted. The main source of interest in the 

 principle of relativity is the revolution which it 

 demands in the concepts of space and time. It is 

 not 1 as\ for most people to accommodate them- 

 selves to the changes which they are asked to 

 make- in these fundamental elements of their 



