85« 



NATURE 



[DECEMBEk 15, 192. 



it doubtlessly works till rij{ht in Phj!. U-froy's own 

 department, a restriction is inevitably placed on the 

 circle of those who might use the volume- particularly 

 outside the British Isles. Anyway, this is the plan 

 upon which the student is intended to procci ! 



In ' n of the volume the 'f 



eight jKisi or picstiit students of the Imptii.n v .-nige 

 have been enlisted — a certain number of orders having 

 been allotted to each. The necessary information 

 having been collected and written up, the whole was 

 then, presumably, sifted and edited by Prof. Lefroy. 

 This unorthodox method has its pitfalls. The various 

 sections, each of which is devoted to a separate order, 

 are of rather unequal merit — as might be expected — 

 the one devoted to the Neuroptera being probably 

 the host. Also, tlic Iwok contains a number of 

 misprints whit h suL;L;ist hurried proof-< "in ' img, and 

 contains errors whicli, if repeated in an examination 

 paper, wouUl tell considerably against a candidate. 

 For examj)lt , tm p. 10 the extra spiracles of Japyx are 

 stated to be on the prothorax : on p. 41 the cervical 

 sclerites are mentioned as articulating the thorax to 

 the abdomen : on p. 87 the mandibles of the nasute 

 caste of termites are stated to form a kind of beak 

 through which a secretion can be exuded at will : on 

 p. 457 Glossina is credited with dropping its larvae 

 one at a time while in flight. 



On the other hand, almost all the families of insects 

 are mentioned, and most of them treated separately, 

 which, in itself, is quite an achievement : in some cases 

 even the sub-families are enumerated and commented 

 on. The book also contains a good deal of information 

 not otherwise very accessible. It is admirably printed, 

 but the price seems rather high. The four half-tone 

 plates are excellent, and the text-figures, for the most 

 part, serve their general purpose. A. D. I. 



Photographic Science. 



Photography as a Scientific Instrument. A Collective 

 Work by A. E. Conrady, Charles R. Davidson, 

 Charles R. Gibson, W. B. Hislop, F. C. V. Laws, 

 J. H. G. Monypenny, Dr. H. Moss, Arthur S. Newman, 

 Dr. Geo. H. Rodman, Dr. S. E. Sheppard, W. L. F. 

 Wastell, Wilfrid Mark Webb, Col. H. S. L. Winter- 

 botham. (Applied Physics Series.) Pp. vii + 549 + 

 2I plates. (London, Glasgow and Bombay : Blackie 

 and Son, Ltd., 1923.) 305. net. 



OWING to the enormous advances which have been 

 made in the various branches of science, recent 

 years have seen the publication of numerous mono- 

 graphs written by specialists in one particular domain. 

 Chemistry and physics have been well catered for in 

 NO. 2824, VOL. 112] 



this respect, but, at all events in C ; 

 been no series of monographs deal I 

 a subject which may be considered as l^elonging 1 

 physical chcmistr>'. Thr present book, to some 

 supplies this want. It (insists of fourteen ( 

 written by thirteen diflferent men, each of whom is ;.:i 

 a< knowledged authority on the subject about w ' ' ' 

 writes. Although it would not be correct to .. 

 the various chapters as monographs, since a compl< t. 

 description of the particular branch under consideration 

 is not attempted, yet in each one is brought together a 

 mass of knowledge which has hitherto been scatters] 

 far and wide in the literature, or has remained embodi( <i 

 as *• experience " with individual workers. 



The first four chapters treat of the histor>', optics, 

 and chemical and physical processes of photography : 

 they may be considered as dealing with the more purclv 

 scientific side, whilst the remaining ten chapters treat 

 of the application of the art in various I.ranrhr<; of 

 science and technolog)-. 



When dealing with a book of this kmd the reviewer 

 is necessarily subject to limitations : he cannot have a 

 knowledge of all the subjects treated, and consequent! \ 

 is attracted by some chapters rather than others. From 

 the purely scientific point of view, those due to Prof. 

 Conrady and Dr. Sheppard are especially worthy of 

 mention. The former bases his treatment of the photo- 

 graphic lens system on the Abbe form of the general 

 theory, and deals with it from the point of view of the 

 user rather than that of tfie designer and computer. 

 The properties of lens systems, and the various classes 

 of aberrations to which lens systems are subject, are 

 treated in a surprisingly simple manner. The practical 

 photographer will be especially interested in " The 

 Experimental Determination of the Constants for any 

 Lens System," and with the explanation of depth of 

 focus, ghost images, flare spots, etc. He will also find 

 that a perfect lens system is impossible, the best 

 obtainable being the result of a large number of com- 

 promises leaving always small residuals of aberration. 

 Such knowledge is important to the purchaser, who will 

 not then expect too much from the makers or 5:tll. rs 

 who are generally silent on such points. 



Since all the applications of photography depend on 

 having the necessary sensitive material with which to 

 work, it is natural that Dr. Sheppard's chapter is the 

 longest in the book. The author has been, so to speak, 

 " bom and bred " in the subject, and, possibly because 

 of this, in some of his publications he has been apt to 

 forget that his readers have not the same acquaintance 

 with the subject as he has. In this chapter, however, 

 Dr. Sheppard has not fallen into this error, and the 

 reviewer does not know of any other account which 

 covers the facts so clearly and lucidly. One failing. 



