252 



NATURE 



[November 5, 1914 



force would at once show that this is the case, 

 and that the uhimate result of both laws is that 

 the property of a given conductor which we call 

 its " resistance " is a constant under certain 

 conditions. 



Again, we greatly object to the common prac- 

 tice of dragging in Ohm's law in connection with 

 the magnetic circuit. Since the reluctance of the 

 iron parts is not independent of the flux, even the 

 mathematical analogy is very imperfect. There 

 is no real analogy at all, for in the magnetic case 

 nothing flows, and there is no continual genera- 

 tion of heat while the flux exists. A comparison 

 with Hooke's law about stress and strain would 

 be much more sensible. 



Bearing in mind that it is intended to be a 

 beginners' book, and that much detail is therefore 

 not to be expected in the more advanced and 

 technical portions, these are really the best; in- 

 deed, the last two chapters give excellent sum- 

 maries of the leading facts about the discharge 

 of electricity through gases and about electrical 

 oscillations. David Robertson. 



OVR BOOKSHELF. • 



Lehrbuch der vergleichenden Mikroskopischen 



Anatomie der Wirbeltiere. Edited by Prof. 



Dr. A. Oppel. VII. Teil, Sehorgan, by Dr. V. 



Franz. Pp. x + 417. Price 18 marks. VIII. 



Teil, Die Hypophysis Cerebri, by Dr. W. 



Stendell. Pp. x+i68. (Jena: G. Fischer, 



1913-14.) Price 8 marks. 

 We have on former occasions expressed a high 

 opinion of the " Comparative Microscopic Anatomy 

 of Vertebrate Animals," now appearing under the 

 editorship of Prof. Oppel. The parts here noticed 

 (Nos. 7 and 8) deal with the eye and pituitary 

 body, and maintain the high standard set by the 

 earlier parts. In systematising our present know- 

 ledge of the various forms assumed by the eye 

 in vertebrates. Dr. Franz has utilised more than 

 650 papers published in recent scientific journals, 

 and in the light of his own researches grouped a 

 multitude of facts together, so that his text and 

 numerous illustrations form a consecutive treatise 

 as well as a most valuable encyclopaedia for refer- 

 ence. He describes the minute structure of each 

 part of the eye in turn — the retina, vitreous body, 

 pecten, choroid, ciliary body, etc., tracing the 

 variations undergone by each throughout the 

 ramifications of the kingdom of vertebrate 

 animals. The opening chapter deals with the 

 visual cells of amphioxus ; the closing one with the 

 structure of the eye of species in which the sense 

 of sight has been impaired or lost from disuse. 



Dr. Walter Stendell 's monograph on the pitui- 

 tary body is of particular value at the present 

 time. Until some thirty years ago this apparently 

 unimportant structure was regarded as merely an 

 interesting morphological puzzle. Our estimate 

 was suddenly changed in 1886, when Dr. Pierre 

 Marie discovered that the remarkable disease he 

 •Nrn 01 An -irni n/i"l 



described under the name of acromegaly was ac- 

 companied by a pathological enlargement of the 

 pituitary body. It was then realised that what 

 was supposed to be merely a small vestigial 

 organ had a direct power of regulating and in- 

 fluencing the growth of the body. Embryologists, 

 morphologists, physiologists, and pathologists 

 then concentrated their attention on it, and the 

 results of their labours may be seen in Dr. 

 Stendell 's pages, particularly in his long biblio- 

 graphical list. We are glad to note he gives due 

 prominence to the pioneer researches of Sir Ed- 

 ward Schafer and of Prof. P. T. Herring. 

 Thresholds of Science. Astronomy. By C. Flam- 



marion. Pp. xi+191. (London: Constable 



and Co.) Price 25. net. 

 The name of the author provides a guarantee of 

 the soundness of the principles and the accuracy 

 of the details expounded in this elementary intro- 

 duction to astronomy by the eminent French 

 astronomer. The book is essentially one for young 

 readers, and the subject-matter is presented in a 

 manner both lucid and interesting. The niimerous 

 illustrations are good, and aptly illustrate the text. 



Commencing with the physical conditions of the 

 earth, its motion and the resulting phenomena are 

 treated at length, special attention being paid to 

 the functions of the sun. A survey of the heavens 

 with the constellations follows, and our relation 

 to the "fixed stars" is made plain. The members 

 of the solar system are treated individually, and 

 their relations to each other in the system are 

 efficiently illustrated. While dealing with the 

 moon M. Flammarion introduces an interesting 

 feature in a revue of the various mythical 

 "Journeys to the Moon." The book concludes 

 with a brief discussion of comets, nebulae, and 

 star clusters. j 



Although, as we are told in a footnote, i 

 " M. Flammarion naturally uses French meas- 

 ures " throughout the book, and the equivalents of 

 the kilogram and kilometre are given, it would 

 probably have been better had our own system 

 of units been employed. The exercise in mental 

 arithmetic required to obtain an estimate of the 

 magnitude involved is very liable to break the 

 continuity of thought, especially among the class 

 of readers for whom the book is intended. 

 Bacofi's New Contour Wall Map of Scotland. 



Scale, I :3i6,8oo, or 5 miles to one inch. Size 



48 by 60 in. (London : G. W. Bacon and Co., 



Ltd.) Price 165. 

 This new edition of a well-known wall map will 

 be welcomed in schools. It is drawn on a conical 

 projection with true meridians of longitude and 

 errorless parallels 55° 30' and 58° north latitude. 

 The main orographical features are shown in the 

 familiar shades of green and brown, and sea 

 depths in blue tints. The lettering is such that it 

 does not interfere with the scheme of colouring, 

 and the railways, which are shown in red, are 

 easily followed. The map can be obtained 

 mounted and varnished with rollers to hang on 

 the wall, or mounted with eyelets and cut to 

 fold. 



