January 25, 19 12] 



NATURE 



409 



in comparison to 700,000 pure-blood whites. So that 

 if the Government of Cape Colony can conduct its native 

 affairs with little or no difficulty, scandal, or injustice, 

 the same thing- ought to be possible for the Transvaal 

 and Natal. H. H. Johnston. 



ENCYCLOPEDIC PHOTOGRAPHY. 



Cassell's Cyclopaedia of Photography. Edited by 

 Bernard E. Jones. Pp. viii+572. (London : Cassell 

 and Co., Ltd., 1911.) Price los. 6d. net. 



THE encyclopcedic arrangement has both advan- 

 tages and disadvantages. One important advan- 

 tage is the possibility of including out-of-the-way 

 matters that could scarcely be referred to in a sys- 

 natic treatise without devoting an unjustifiable 



laount of space to their consideration. The editor 

 has made the very most of this possibility, for we find 

 such headings as "Bicycle" and "Contact Breaks," 

 the connection of which with photography is rather 

 remote, and others, such as "Tea-tray Landscapes" 

 and "Thought Photography," which must occur very 

 rarely indeed in photographic or any other literature. 

 Of the few headings that we have sought for to test 

 the inclusive character of the volume, the only ones 

 that we fail to find are " Metallog-raphy," a common 

 enough word that stands for a very important branch 

 of photography at the present time, and " Rainbow," 

 to which the reader is specifically referred at the end 

 of an article on " Cosmical Photography." 



An advantage often claimed for the alphabetical 

 arrangement is facility of reference, though this can 

 scarcely be greater than in the case of a treatise with 

 a good index. The editor appears to have been un- 

 duly anxious with regard to this matter, for in some 

 cases he has, in our opinion, failed by reason of the 

 excessive subdivision of the subjects. For example, 

 some shutters are described under the heading 

 "Shutters," where we expected to find the whole sub- 

 ject treated of. But other shutters are given under 

 " Flap Shutter " and " Focal Plane Shutter," and 

 before we get all that is given on this subject, we 

 must read also the various sections, " Instantaneous 

 Shutters," "Shutters, efficiency of," "Shutters, test- 

 ing," and possibly others that we have not come 

 across. And this is not exceptional, for spectroscopy 

 appears to be distributed among nearly a dozen head- 

 ings, and astronomical photography and the use of 

 polarised light, among other subjects, are similarly 

 subdivided. 



The editor has been perhaps rather too ambitious, 

 least in his preface, for he refers to the volume as 



surveying the whole field of photographic know- 

 ledge," and being "at once authoritative and com- 

 okte." The work " is intended not only for the 

 utical photographer, but also for the scientific 

 dent" who will find articles "valuable, because 

 horitative." "The manufacturer, too. . . ." The 

 authoritative character of an article depends upon the 

 author and upon him alone, and the real student 

 always desires to know upon whose authority the 

 statements that he reads depends. A very few articles 

 signed, but there are many and among them 



IV excellent articles that are not only not signed, 

 NO. 2204, VOL. 88] 



but to the authorship of which there is no clue, even 

 in the list of chief contributors and the nature of 

 the subjects with which they deal. The authorship in 

 some cases is obvious enough to those acquainted with 

 photographic literature, and some of the articles would 

 have gained rather than lost by having their source 

 clearly indicated. 



When a volume is written by nineteen "chief con- 

 tributors," and presumably other contributors in addi- 

 tion, it is impossible that its sections shall be equally 

 "authoritative," and, as a matter of fact, they are 

 of very various degrees of merit. Many are all that 

 could be desired within their limits, giving a concise, 

 clear, and inclusive summary of the subjects with 

 which they deal. But in some the subject is evaded, 

 as in " Shutters, testing," where, after a quarter of 

 a page of information, we read that "there are 

 numerous other methods, most of which, however, 

 call for special apparatus," and the reader is left in 

 the dark with regard to these "numerous other 

 methods." Some are obscure, and we doubt whether 

 Mr. Dallmeyer himself would have recognised the 

 "Adon" lens that he invented from the description 

 given of it. "Polarisation" is defined as "The split- 

 ting up or division of a ray of light into two distinct 

 refracted parts," and here the student is left to 

 ponder the matter with no diagram to help him, 

 though there are "hundreds of line drawings in the 

 text " (as stated on the title-page), and some, such as 

 those of a "porcelain evaporating dish " and a "clamp 

 for general use," might well have given place to 

 others more helpful. As might be expected, the 

 volume is not free from errors. Cedar-wood oil is 

 not volatile; the Abbe two-lens condenser is not of 

 low numerical aperture; aiid it is not correct to say 

 that "the focal lengths of the microscope objectives 

 in general use range from 3 in. to i^ in.," even if we 

 add that "lenses of both lower and higher power are 

 manufactured." We do not understand how a photo- 

 graph taken on an isochromatic plate with a " six- 

 times " yellow screen can be "over-corrected," nor 

 how "beads of dried paste, jnade with magnesium 

 powder and distilled water," could be used instead of 

 limes for the limelight. But looking at the book as a 

 whole we can safely say that the discriminating: 

 student will find in it a great fund of inforniafion. 

 and that a reference to it will somotini< s sav(> him 

 prolonged if not fruitless search among rare, litlK-- 

 known, and old records. C. J. 



MATHEMATICS FOR TEACHERS. 

 Lectures on Fundamental Concepts of Algebra and 

 Geometry. By Prof. J. W. Young. Prepared for 

 publication with the cooperation of W. W. Denton. 

 With a note on the Growth of Algebraic Symbolism 

 by Prof. U. G. Mitchell. Pp. vii+247. (New 

 York : The Macmillan Co. ; London : Macmillan 

 and Co., Ltd., 191 1.) Price 75. net. 



THIS book contains a series of lectures on some 

 of the fundamental principles of mathematics, 

 treated from the most recent and scientific point of 

 view; that is, mainly with reference to their con- 

 sistency and the nature of the assumptions involved. 



