UCTl »BER 17. [918 



NATURE 



and America arc described and discussed, while 

 the section dealing with adsorption has been ex- 

 tended so as to include an account of recent work 

 in ibis field. 



\ description is also given ol several new prac- 

 tical methods. Amongsl these may be mentioned 

 Morgan's method for determining the molecular 

 weights ol liquids from tin- weight of falling drops, 

 and the methods suggested by Smith and 

 Menzies for the determination of the boiling points 

 and vapour pressures ol substances 



From the examples which have been given, it 

 will be evident that, with one or two exceptions, 

 the book has been brought thoroughly up to date, 

 and can be confidently recommended to anyone 

 desirous of having a clear and comprehensive ac- 

 count oi modern views relating to such subjects 

 as the properties ol atoms and molecules, and the 

 general properties of gases, liquids, and solids. 



J. K. W. 



OPTICS IN EUCLID'S TIME. 

 L'Ottica di Euclide. By Prof. G. Ovio. ("Manuali 

 Hoepli.") Pp. xx + 415. (Milano : Ulrico 

 I [oepli, 1918.) Price 7.50 lire. 



IT need scarcel) be pointed ou-t here that the 

 greater portion of what we now call "optics," 

 dealing as it does with applications of the laws 

 traction, was unknown in the days of the 

 geometer. In this small volume Prof. 

 eppe Ovio, of Genoa, has condensed an ex- 

 position of the contents of two volumes known 

 as "Optics" and "Catoptrics," of which the first 

 is believed certainly to be due to Euclid, while 

 his authorship of the second is regarded as rather 

 more doubtful. In preparing this book Prof. Ovio 

 has mainly based his work on the editions of l'ena, 



Danti, and Heiberg, but has also consulted those 

 of Gregory, Zamberto, and Freart. 



"Optics Properly So-called," which forms the 

 title of the first portion, is practically equivalent 

 to our perspective geometry. It deals with the 

 apparent dimensions of objects seen at different 



distances and in different directions. It thus con- 

 sists of a collection of propositions really purel) 

 letrical in character. For example, one pro- 

 position proves that an eye situated near a sphere 

 sees less of it than one further off, but the visible 

 portion appears larger, ["here are some theorems, 

 on the other hand, of which the purport and mean- 

 ing are rather vague, and Prof. Ovio's comments 



On these will be found useful. " ! Catoptrics " deals 



with reflection at curved surfaces. The proposi- 

 tions include proofs that a plane mirror produces 

 an inverted image of the same size as the object, 

 that rays after reflection at a concave surface 

 sometimes converge and at other times diverge, 

 and a large number of other properties, of which 

 these maj be regarded as typical representatives. 

 According to Euclid, visual rays emanated from 

 the eye and went to the objects. 



Now that the younger generation no longei 

 acquires its geometrical ideas from Euclid's 

 elements, an interesting variation on our over- 

 NO. 2555. VOL. I02] 



stereotyped school curricula might very well be 

 introduced !■■ all) teaching the subject- 

 matter of this volume. Man\ of the proofs afford 

 quite interesting lessons in deductive methods, 



and could very well lie , lied b\ excellent 



exercises in constructive geomi But, unfor- 



tunately, the subject in its present form does not 

 fall within tin- syllabus ol scho nrnations. 



<.. II. B. 



OUR BOOKSHELF. 

 Descriptive Catalogue "I the British Scientific 

 Products Exhibition, villi Articles mi a, cent. 

 Developments. Pp. xxiv-t 268. (London, 199 

 Piccadilly : British Science Guild, 1918.) Price 

 25. 6d. net. 



The record of industrial achievement during the 

 period of the war shown at the recent British 

 Scientific Products Exhibition organised bv the 

 British Science Guild was much enhanced bv the 

 publication of a comprehensive descriptive cata- 

 logue. Whilst the contained details of the ex- 

 hibits and their technical applications added in- 

 terest to their examination and form a valuable 

 record for reference, the inclusion of a series of 

 articles on recent industrial developments should 

 do much to drive home and explain what has been 

 accomplished during the past four years by the 

 successful co-operation of science and industry, 

 and what is needed for that fuller and more per- 

 manent effort which is required to secure industrial 

 progress and efficiency. The story has been told 

 in man\ forms, but every repetition that can extend 

 an appreciation of the problem is to be welcomed. 

 The catalogue of exhibits contains concrete ex- 

 amples of recent developments which form the 

 basis for the storv, and their direct association with 

 a series of twentv concise and well-written articles 

 by authorities whose names are a guarantee of 

 first-hand knowledge provides a helpful correlation 

 between the results obtained in works and labora- 

 tories and the objects and methods which have 

 secured their realisation. 



Mathematical Papers for Admission into the Royal 

 Military Academy and Hi Royal Military Col- 

 lege, and Papers in Eh m< ntary Engineering for 

 Naval Cadetships, November, 1917, and March, 

 1918. Pp. 40. Elementary Engineering Papers 

 for Naval ('midships (Special Entry) for the 

 Years [913 1 « j 1 — . l'p- 33- Both edited by R. M. 

 Milne. (London: Maemillan and Co., Ltd., 

 mi S. 1 Prii i- of each IS. ?J. net. 

 \ mil \n oi mathematical papers set to candi- 

 dates for admission to the Military Academy and 

 College was reviewed in a recent issue of \ \ 

 The first of the present publications is a further 

 set of such papers. The other book contains the 

 papers in elementary engineering set recent 



examinations for Naval Cadetships. I ns 



in this collection cover the ground of the 

 elementary theory of steam- and g; s-engines, link 

 motions, lathes, etc., and also presuppose some 

 knowledge of the theory of hvd ostatics, heat, and 



