142 



NATURE 



[January 3, 19 18 



of polyphase motor are cases in point. Some of 

 the proofs given are worthy of hig-h commen- 

 dation and will be much appreciated by students. 



(2) A simple description is given of the various 

 kinds of direct-current motors which are in every- 

 day use, and the elementary theory of their action 

 is explained. The problems which interest the 

 designer are barely mentioned, but the practical 

 methods of testing and the requisite calculations 

 are fully described. The wiring connections are 

 given in far greater detail than in ordinary 

 treatises, and this will be of value to working 

 engineers, enabling them to get a thorough grasp 

 of the requisite connections for the electrical 

 devices which they have to use constantly. Many 

 numerical examples are given. We can recom- 

 mend this book to the beginner and to all who 

 wish to understand the working of electric 

 starters, controllers, contactors, automatic lifts, 

 etc. The book is well printed, the diagrams are 

 clear, and the machinery and devices described 

 are of the latest types. 



(3) The author clearly indicates the scope of his 

 book by describing it as a handbook of connection 

 diag-rams of control and protective systems for 

 industrial plants. Considering the limited space 

 at his disposal and the very complicated direct- 

 ^nd alternating-current systems that have to be 

 described, the author has, on the whole, been 

 successful. The reviewer would have liked fuller 

 explanations in places, and some of the diagrams 

 fatigue the eyes. As a book for occasional refer- 

 ence it will prove useful. We notice that in 

 accordance with the practice of many engineers a 

 zigzasr line is used to denote an inductive coil. 

 A helical line, however, is more self-explanatory 

 and practically as easy to draw, and we have good 

 hopes that it will soon be universally used. Recom- 

 mendations to this effect have frequently been made 

 by " symbols " committees in many countries. 



A. Russell. 



GEODETIC BASE MEASUREMENTS. 

 La Mesure Rapide des Bases Gdodesiques. 



Par J.-Ren6 Benoit et Ch.-Ed. Guillaume. Cin- 



qui^me Edition. Pp. 285. (Paris : Gauthier- 



Villars et Cie, 1917.) 

 nPHE use of invar wires in the measurement of 

 -■- bases in geodetic triangulation, as well as in 

 topographical surveys, has become so well estab- 

 lished that a new edition of MM. Benoit and Guil- 

 laume 's handbook on their employment will be 

 welcomed 4 



The fifth edition does not for the most part differ 

 greatly from the previous edition, which appeared 

 in 1908, but an additional chapter has been added, 

 in which the results of later experience have been 

 added. The control of the wires, both by fixed 

 marks laid down in a building with which the 

 length of each wire may be compared, and by a 

 short base on which the wires can be used under 

 field conditions, is discussed. The former is in 

 use in England, France, Egypt, India, and else- 

 where, while at Potsdam a 240-metre base is used. 

 NO. 2514, VOL. 100] 



The permanence of mural control-marks is con- 

 sidered, and the experience of the Bureau at 

 Breteuil shows that the distance between such 

 points of reference should be verified over a con- 

 siderable period of time. 



The results of base measurements at the Simplon 

 tunnel in 1906, in Uganda in 1907, in Portuguese 

 East Africa, the Argentine, Russia, Mexico, and 

 Rumania are given in some detail, as being opera- 

 tions for which the wires were verified at the 

 Bureau ; but these by no means exhaust the list of 

 countries in which the method of measurement by 

 means of wires, initiated by Prof. Jaderin, of 

 Stockholm, in 1890, has been employed. In 1913 

 a base eight and a half kilometres long was mea- 

 sured near Lyon by the Geographical Service of 

 the Army both with invar wires and with an invar 

 4-m. bar, in which the mean values obtained by 

 to-and-fro measurements with the bar and those 

 of two wires differed only by 8*3 mm. 



The need for comparison between the " bases 

 murales " or the control-marks which now exist 

 in several countries is insisted on, and such a com- 

 parison between Breteuil and Teddington had been 

 taken in hand recently, but has been interrupted 

 by the war. The results of investig-ations, which 

 were undertaken on the proposal of Sir David Gill, 

 to ascertain the changes caused in a wire by con- 

 stant use at normal tension are set out; and the 

 results of the comparison made with twelve wires 

 from four to six times yearly over the period 1908 

 to 1916 in continuation of an earlier series, 1904 to 

 1907, show well the stability of these wires when 

 carefully handled under favourable conditions. 



Three notes on the expansion of invar and the 

 effect of mechanical and thermal treatment upon 

 it conclude this very useful handbook on the use 

 of these wires in field measurement, and the pre- 

 cision which may be attained with them. 



More can be said regarding the practical use 

 of these wires in the field and the various diffi- 

 culties that have from time to time been en- 

 countered ; but as these He outside the personal 

 experience of the authors they have not been speci- 

 ally dealt with in this volume. H. G. L. 



PHILOSOPHY. 

 A Defence of Idealism: Some Questions and 

 Conclusions. By May Sinclair. Pp. xxi-f396. 

 (London: Macmillan and Co., Ltd., 1917.) 

 Price 125. net. 



MISS MAY SINCLAIR'S "Defence of 

 Idealism " is written with a most refresh- 

 ing- ease and freedom from technicality. It is the 

 work of an amateur, but of an amateur who has 

 read much and sees how arguments that are 

 usually thought to be abstruse bear closely upon 

 problems which should command the interest of 

 every thinking person. Professional students 

 cannot fail to regard such a book as a gratifying 

 proof of the vitality of philosophy in this country. 

 The idealism which Miss Sinclair sets out to 

 defend is not idealism in general, but idealistic 

 monism. It would have been well if Miss Sinclair 



