July 21, 1910] 



NATURE 



69 



iiiiTiong the advantages of the scheme will be that each 

 -volume can be brought up to date independently of the 

 rest. 



The forty sections are classified in the two main 

 divisions of "pure sciences" and "applied sciences." 

 Each of these is again subdivided into mathematical, 

 inorsjanic, and biological sciences. Each subdivision 

 comprises a certain number of sections, and each 

 section has its own editor. The general editor is Dr. 

 Toulouse, of the Ecole des Hautes Etudes, and 

 among the editors of sections are included such names 

 as Painlev^, Mascart, Leduc, Lacroix, Bertrand. 



The volume under review belongs to the section of 

 " Industries physiques " in the division of applied 

 sciences — subdivision, inorganic. The section is to 

 include volumes on such subjects as " Industrial Elec- 

 tricity " (two vols.), " Electric Motors," " Electric 

 Traction," "Electric Lighting," "Rheostats," "Wire- 

 less Telegraphy," "The Liquefaction of Gases," "The 

 Industrial Production of High Temperatures," &c. 

 This volume on "Optical Instruments for Observation 

 and for Measurement" would seem to be the first 

 volume of the section to be issued. 



Judged from its position in this hierarchy of scien- 

 tific knowledge, Captain Raibaud's volume is perhaps 

 a little disappointing. One might expect to find de- 

 tails of the most recent technical advances, of such a 

 character that the skilled optician might there find 

 help, -whether as regards difficulties of design, or of 

 construction, or. methods of ensuring accuracy. In 

 the present instance, however, questions not only 

 as to calculation of the optical system, but as to con- 

 struction and methods of test, are definitely excluded ; 

 the aim is thus only to give a general account of the 

 optical properties of various types of instrument, with 

 brief particulars of individual instruments and designs. 

 Expressed shortly, the work is rather an educational 

 text-book than a technical handbook. 



From this point of view, however, and for the 

 general reader who wishes to obtain an intelligent 

 knowledge of the more essential optical properties and 

 possible defects of an instrument which he may be 

 in the habit of using, the book can be cordially recom- 

 mended. More especially, the general conditions 

 governing the formation of satisfactory images by an 

 optical instrument are carefully and clearly discussed. 

 Thus the first part of the work, more than one-third 

 of the whole, deals with the general properties of 

 instruments, definition and resolving power, bright- 

 ness of the image, extent of field of view in breadth 

 and depth, distortion, magnification — subordinate, as 

 is rightly emphasised, to resolving power and defini- 

 tion — and the functions and limitations of the eye in 

 conjunction with an optical instrument. The char- 

 acteristics of binocular vision and of vision through a 

 binocular instrument are also examined, and, in regard 

 to measuring instruments, the general conditions 

 affecting accuracy. 



In the second part of the book the instruments 

 considered are those of the telescope class, the micro- 

 -scope, the photograpjiic objective, instruments for 

 measuring angles, surveying instruments and tele- 

 meters, and, finally, instruments based on the prin- 

 ciple of auto-collimation. The list, of course, is by no 

 NO. 2125, VOL. 84I 



means exhaustive; laboratory instruments, the spectro- 

 scope, interferometer, &c., and photometric apparatus 

 generally are not included, nor does space admit of 

 detailed consideration of any one type. The book 

 is, however, written by one who has had experience 

 in handling the instruments he describes, and 

 thoroughly familiar, not only with the optical theory, 

 but also with the practical points affecting their 

 performance. 



OUR BOOK SHELF. 



Methods used in the Examination of Milk and Dairy 

 Products. By Dr. Chr. Barthel. Translation by 

 W. Goodwin. Pp. xii + 260. (London : Macmillan 

 and Co., Ltd., igio.) Price 7s. 6d. net. 

 This edition contains several additions to the original 

 work of Dr. Barthel, and it will be found very useful 

 to those engaged in examining milk and dairy prcN 

 ducts on a large scale. The general remarks in it 

 apply more exacth' to milk of German or Swedish 

 origin than to milk from some British breeds of cows. 

 In the notes on the physical examination of milk 

 are useful hints as to the estimation of dirt. For the 

 determination of fat Soxhlet's araeometer method is 

 still given a prominent place, though in most places 

 it is superseded by less complicated and more certain 

 methods. Wollny's refractometer method for the fat 

 estimation, if carried out under exact conditions, 

 seems to give very accurate results, but it is so sensi- 

 tive that the least departure from the necessary condi- 

 tions influences the results seriously; one advantage 

 it possesses is that as many as 150 determinations may 

 be made in an hour with the proper appliances and 

 accommodation. The Rose-Gottlieb method, and 

 various modifications of centrifuge methods, includ- 

 ing some not requiring the use of strong sulphuric 

 acid, are described. Tests for adulterations, artificial 

 colouring matters, and preservatives are given. 

 Saccharate of lime is said to be one of the latest 

 adulterations of milk and cream ; it increases their 

 viscosity and gives them the appearance of being 

 richer in fat; a method for its detection is given. 



Methods for the analysis of butter, cheese, preserved 

 milk — including Buddised milk, that is, milk treated 

 with a small quantity of hydrogen peroxide — con- 

 densed milk, and desiccated milk are given. We find 

 also some account of the decomposition products of 

 milk, butter, and cheese; and, in an appendix, several 

 tables of figures useful in calculating the results of 

 analyses. 



Norwegian and Other Fish Talcs. By Bradnock 

 Hall. Pp. x + 243. (London : Smith, Elder and 

 Co., 1910.) Price 55. net. 

 This is ft frankly trivial book with a quite unin- 

 telligible dedication in place of a preface. The illus- 

 trations are excellent, and the text makes good holiday 

 reading, notwithstanding its somewhat strained 

 humour, .-^s the author says, "the diaries of anglers 

 are not as a rule interesting, even to sympathetic 

 brethren of the craft," but we think that many of 

 the author's own experiences at least come near to 

 proving exceptions to his own generalisation. Inci- 

 dentally, we are told of certain Norwegian fish : — 

 " Evervone thought they were salmon, but both turned 

 out tn'be sea-trout when the shape of the gill coveiis 

 and the tail bones were examined." It seems a pity 

 that the precise differences between salmon and sea- 

 trout in the shape of the gill covers and tail bones are 

 not divulged for the benefit of fishermen and natural- 

 ists; the counting of scales in a transverse series is 

 none too easv, and an alternative method of diagnosis 

 (if such really exists) would be welcome. 



