November, 1906.] 



KNOWLEDGE & SCIENTIFIC NEWS. 



595 



MATHEMATICS. 



A System of Applied Optics. H. Dennis Taylor (Messrs. 

 Marmillan and Co., 30s. net). — This is a notable book. 

 .Although many of the most important advances in optics 

 have been made in England, there has been in recent years 

 no text-book in England written from a practical standpoint 

 similar to the important technical treatises of Czapski and 

 Rohr published in Germany. Academical treatises there arc 

 in abund.-mce and of high quality, but the standpoint from 

 which these are written is such that in none of them is the 

 subject treated in such a way as to enable a reader directly 

 to calculate the form of lenses necessary for producing 

 an efficient combination. This is the more astonishing 

 inasmuch as Mr. Taylor, who now succeeds in supply- 

 ing the deficiency, does so on the basis, not of any foreign 

 text-book, but of an old English text-book, viz., Codding- 

 ton's treatise on the reflection and refraction of light. The 

 chief object in the present volume has been " to arrive at a 

 complete system of algebraic formute of the second order 

 which can be applied to any optical system likely to occur in 

 practice with results which, in general, very closely ap- 

 proach to accuracy." This is done with the employment of 

 quite simple algebra, so that no one need be deterred from 

 reading the book on account of deficiencies in mathematical 

 equipment. The reader is supposed to be already acquainted 

 with the usual formulae of the first appro.ximation. He must 

 master a new convention in regard to signs which at first 

 sight looks somewhat elaborate, but which works out very 

 well in the sequel. When so many conventions already exist 

 no concern need be felt at the creation of a new one. We 

 have nothing but admiration for the way in which the sub- 

 ject is developed, leading to formulae which include and run 

 parallel to .Seidel's famous five conditions which require 

 satisfaction in the production of a combination perfect to 

 the second order. It is impossible to go into detail in re- 

 gard to the general treatment. The characteristic note is 

 the great freshness and originality everywhere displayed. 

 There is no doubt at all that the treatise will rapidly take its 

 pro])er place as one which will bring back to England its 

 original prestige in optical matters. In regard to the style 

 of publication there are two matters for regret. It is a pitv 

 that the numerous diagrams do not immediately accom- 

 p;my the text which they illustrate, but are collected together 

 in the old-fashioned way in groups upon plate pages. It is 

 also a pity that there is no index, although the orderly de- 

 velopment of the subject makes this omission less important 

 than it otherwise would be. 



PHOTO(iRAPHY. 



The Year-Book of Photograpliy. Edited by F. J. Mor- 

 timer, F.R.P..S. (London: "The Photographic News"; 

 price IS.). — This annual has gone through many changes 

 since it was established nearly fifty years ago. After a lisi 

 of .Societies, there follows a vast collection of formula; that 

 have reference to negative making, and then eight excellen*. 

 articles on printing processes by as many different authors, 

 with a largo collection of formula; appended to each, and 

 llicn more formulcE and tables. Apparently all the instruc- 

 tions of the principal makers of photographic materials are 

 included, and the source of these is obvious, but we should 

 like to have seen the authorities given for a large number o( 

 formula;, the sources of which are not acknowledged, and 

 some of which are called " standard." We would' suL'y^rst 

 that this collection of formulse might be suitably tabu- 

 l;ited or brought into some system of expression, for then 

 lh(y would be much more useful to many who do not 

 slavishly adhere to one maker's instructions, and those wh ) 

 do this can always get what they want from the maker 

 whose goods they use. One example of the desirability 

 -for editing such a collection will suffice as an illustration. 

 The two following are given on opposite pages ; the source 

 of the first is not stated, the second is headed " Rotary 

 .Stripjiiiig I'-ilms." Thev are sensitizing solutions for carbon 

 tissue. 



Potassium bichromate 



Water 



Ammonia ( SiSo) 



20-30 ozs. 

 60 mins. 



I 

 35-50 grms. 



1000 CCS. 



6 CCS 



I oz. - 30 grms. 



30 ozs. -900 CCS. 



I drm.- 35 CCS. 



Obviously this is the same formula, and it need not 

 have been set down twice, but the metric equivalents are 

 peculiar. How one ounce can have the variable metric 

 equivalent in one case and a quite different equivalent 

 in the other, how 30 ozs. in the metric system can 

 be less than 20 to 30 ozs., and as 60 minims are equal to one 

 dram, how the metric equivalents can be so different as 

 shown, would puzzle even an experienced worker. 



Chemistry for Photographers. By Chas. F. Townsen<l. 

 F'ourth Edition (London : Dawbarn and Ward, Ltd. ; price 

 IS. net.). — When a book has run to four substantial editions 

 it may well claim to have established itself, and in a measure 

 to be above criticism. However, the author can claim that 

 he is only following in the footsteps of Hardwich and others 

 in associating the word chemistn' with photography more 

 closely than seems to be justifiable. There is no chemistry 

 involved in the publication of formulas of solutions and the 

 description of the operations of photography. It would 

 have been better if the author had considerably restricted 

 the scope of the book, for when " printing in salts of iron •' 

 occupies two pages, "printing in platinum" less than three, 

 " orthochromatism " less than two, and so on, after prac- 

 tical instructions and formula; have been given, there Is 

 little room for any chemistry. 



ZOOLOGY. 



A Text-Book in General Zoology. By II. R. Linville and 

 H. A. Kelly ^Boston, New \urk, Chicago, and London, 

 Ginn and Co., 1906, pp. x. 4- 462, illustrated ; price 7s. 6d.). 

 — In this profusely illustrated little volume the authors — both 

 well-known science teachers in New York— have initiated 

 an entirely new mode of treating their subject. In place of 

 starting with either the lowest or the highest group of 

 animals (Protozoa or Vertebrata), they commence with the 

 .\rthropoda (insects and crusl/iceans), on the ground that, as 

 the result of long practical experience, students can be more 

 satisfactorily instructed on these lines than by any other 

 method. Whether such a course will commend itself to 

 English teachers, time and experience can alone demon- 

 strate. -So far as we can see, the treatment of the subject is 

 remarkably even throughout, thus demonstrating the " all- 

 round " training of its authors, and, when the number of 

 illustrations is taken into account, the book is a marvel of 

 cheapness. W'hether it is not a little stretching terms to 

 speak of the duck-billed platypus as " an ally of the 

 squirrel," may, perhaps, bo legitimate criticism. 



MISCELLANEOUS. 

 George Bentham. by D. Daydon Jackson ; pp. xii and 292. 



English Men of .Science Series (f)ont and Co. ; 2S. 6d. net.). 

 — .\s a botanist Bontham's reputation is .secure, his achieve- 

 ments in this respect and the influonce for good exercised 

 by his soiuid knowledge of plants have been told elsewhere. 

 The book under consideration will prove a n-velation to 

 many whose impressions respecting Bentham's character 

 were formed from a casual interview in connection with 

 scientific work, for although invariablv courteous and sym- 

 pathetic, his shy and reserved manner often suggested the 

 idea that he was bored. Bentham commenced the study of 

 botany as a boy, and thanks to his rank of birth and oppor- 

 tunity for rambling over Europe at an early age, he became 

 acquainted with the leading European botanists, and 

 familiarised himself with the floras of various countries con- 

 taiii.xl in national herbaria. lie studied for the Bar in a 

 half-hearted manner, and finally derided to devote himself 

 entirely to botany. Having determined on this course, he 

 settled down to work in a methodical manner, and aided 

 by good health, the possession of ample means, and a keen 

 power of discrimination, he practically revised and placed on 

 a truer scientific basis the flora of the world. Jackson 

 reve.als th.it, when off duly, Bentham in spile of his profound 

 scientific knowledge was a society man, a lover of music, 

 enjoyed whist, and was beloved by everyone whose good 

 fortune it was to enjoy his friendship. 



Brass and Iron Founding, by Joseph E. Dangcrfield, is 

 one of Messrs. Dawbarn and Ward's " Home-Workers' 

 Series " (price 6d. net). — This is a thoroughly practical little 

 book, which should prove of the greatest use to all those 

 who have to undertake such work. 



