316 



NATURE 



\yan. 



I. li 



Typographical errors are rather numerous ; but these, 

 with few exceptions, are corrected in the page of errata 

 inserted after the title-page. 



Prof. Rosenbusch's " Tables for the Microscopic De- 

 termination of Minerals in Rocks " is one of the most 

 useful compilations which have appeared for some time. 

 It has doubtless been suggested by, and to some extent 

 modelled on. Dr. E. Hussak's "Anleitungzur Bestimmung 

 des gesteinsbildenden Mineralien," which, in spite of 

 numerous inaccuracies, was found to be in such demand 

 among students that soon after its publication it was 

 translated into English, errors and all. Tables of this 

 kind are sure to be favourably received by the practical 

 worker, on account of the saving in time and labour 

 resulting from their use, a single glance being sufficient 

 to obtain all the requisite information about a given 

 mineral. The book consists of nine two-page tables, in 

 which we find recorded data concerning the cleavage, 

 form, crystallographic development, colour, pleochroism, 

 indices of refraction, optic orientation, dispersion, crystal- 

 system, specific gravity, behaviour with reagents, and 

 chemical composition of all the minerals occurring in 

 rocks, whether as essential or accessory constituents. 

 Many will be surprised to hear that these amount to as 

 many as 190. There can be no hesitation in predicting a 

 wide circulation for this very serviceable little book. An 

 English edition is being] prepared, we understand, by 

 Messrs. Swan Sonnenschein and Co. 



"Les Mine'raux des Roches," by Messrs. A. Michel- 

 L^vy and A. Lacroix, is a more elaborate work, dealing 

 with the same subject. This book, as we are informed 

 in the preface, is complementary to the " Mineralogie 

 Micrographique," published in 1878 by the first-named 

 author in collaboration with M. Fouque. It is divided 

 into two parts : (i) the application of optical and 

 chemical methods to the microscopical study of mine- 

 rals, by A. Michel-Ldvy alone ; (2) a descriptive 

 summary of the principal minerals occurring in rocks, 

 by both authors. 



The first part contains a mathematical exposition of 

 the optical properties of minerals, which, though tending 

 occasionally to abstruseness, is characterized by a true 

 French elegance of treatment, the excellent use made of 

 curves in representing graphically the variation of ex- 

 tinction-angles being especially worthy of commenda- 

 tion. On 'p. 54 we have a description of an instrument 

 for the measurement of double refraction, which has been 

 constructed for the author by M. Nachet, the celebrated 

 Parisian microscope-maker. The comparateur, as it is 

 .named by its inventor, consists of a special eye-piece, to 

 which is attached an arrangement of prisms. and lenses, 

 by which the tint and luminous intensity of a given 

 mineral can be compared with those of a movable quartz 

 wedge. A series of measurements of the double refrac- 

 tion of the principal rock-forming minerals, made by the 

 authors with this instrument, follow on p. 66, together 

 with the colours presented by plates of o-qi, 0-02, and 

 0*03 mm. respectively. At the end of the book there is 

 also a magnificent plate, representing Newton's scale of 

 colours up to the fifth order. By an ingenious con- 

 trivance, the colours given by the different minerals are 

 shown for thicknesses ranging between o and o"o6 mm. 

 In the second part of the book the minerals are 



arranged in accordance with a scheme which is partly 

 alphabetical, partly systematic— /.d". the members of a 

 natural group {e.g. the felspars, micas, amphi boles, and 

 pyroxenes) have not been separated. This method is, 

 perhaps, not quite satisfactory, as the advantage of an 

 alphabetical arrangement is in great part lost, while at 

 the same time the systematic classification is necessarily 

 incomplete. But reference to the minerals is much 

 facilitated by an excellent index. 



This part of the book contains a number of new deter- 

 minations made by the authors, who have "endeavoured," 

 and let us add with success, " to make it as complete as 

 is consistent with the present state of the science." It 

 concludes with a synoptical table, in which the optical 

 data are again briefly recapitulated. F. H. H. 



SEWAGE TREATMENT, PURIFICATION, 

 AND UTILIZATION. 

 Sewage Treatment, Purification., and Utilization. By 

 J. W. Slater, F.E.S. (London : Whittaker and Co., 

 1888.) 



T^HIS is the work of an advocate of chemical pre- 

 -L cipitation processes for the treatment of sewage. 

 It cannot claim to be an impartial review of the " sewage 

 question," for the bias of the author is exhibited in nearly 

 every page. The author is evidently of opinion that his 

 case is likely to derive support from what is known as 

 argumentum ad hominem, or abuse of the other side 

 (those who hold different views from his own). The 

 Rivers Pollution Commissioners come in for a consider- 

 able share of these attentions, as the following passages 

 will show : — " Such a man was by nature qualified for a 

 Royal Commissioner, who can never admit that either 

 himself or any of his predecessors can have been mis- 

 taken " (p. 165). The spoiling of an efBuent from a 

 chemical precipitation process by fermentation of the 

 deposited sediment is spoken of as a result "to gladden 

 the heart, and for once justify the representations of ex- 

 Royal Rivers Pollution Commissioners " (p. 172). " Mr. 

 j Bailey-Denton— who seems to be to Prof Frankland what 

 Ali was to Mahomed and Mr. Grant Allen to Charles 

 Darwin " (p. 79). The Royal Commissioners on Metro- 

 politan Sewage Discharge are alluded to in the following 

 terms (p. 86) : " That Commission refused or neglected — 

 and in such a case these two terms are nearly equivalent — 

 to examine fully and fairly into the merits of precipitation. 

 ... It would not, or at least did not, visit Aylesbury. 

 It was satisfied to condemn precipitation on the faith of 

 the archaic reports of the Royal Rivers Pollution Com- 

 missioners, reports which, if true at the date when 

 written — and this is a fairly strong concession — are 

 demonstrably false if applied, e.g., to the process now in 

 operation at Aylesbury." 



It will perhaps raise a smile amongst connoisseurs in 

 sewage matters to learn that managers of sewage works 

 require protection from the (dishonourable) tricks of 

 critical visitors. The author, at any rate, believes their 

 innocence is likely to be imposed upon. He writes 

 (p. 168) : — "A few hints may here be given about sampling 

 effluents for analysis or for preservation. I write here 

 mainly for the guidance of officials left in charge of 



