March 29, 1888] 



NATURE 



509 



One would like to see " piles of shot " relegated to the 

 examples, as in these days of rifled guns and elongated 

 projectiles it seems an anachronism. The book is logical 

 well printed, and illustrated by the best set of examples 

 that can be found in any book of the same kind. 



P. A. MacMahon. 



OUR BOOK SHELF. 



My Telescope. By a Quekett Club Man. (London : 

 Roper and Drowley, 1888.) 



This volume is described by its author a§ a simple 

 introduction to the glories of the heavens. It is not 

 designed as a guide to the use of a telescope, but 

 simply to give such an account of its teachings as may 

 interest non-astronomical readers. The main features of 

 the various celestial bodies are described, but, for some 

 reason or other, comets are not considered at all. Most 

 of the descriptions are very meagre ; thus, nebulas and 

 star-clusters are disposed of in a page, and that not 

 closely printed ; even the sun — " the ruler of our system " 

 — is described in a little over three pages. The scantiness 

 of the information given is the greatest fault of the book. 



In the little that the book does contain, many mistakes 

 occur. Thus, the moon is stated to present a marbled or 

 mottled appearance because her surface is unequally 

 refractive (p. 62), and the velocity of light is twice put 

 down as 184,000 miles per second (pp. 46 and 72.) 



The illustrations are moderate, and the book has a 

 generally neat appearance. The place it is to occupy 

 in astronomical literature, however, is not very clear, as 

 there are already many cheaper books in existence which 

 contain the same information, and much in addition. 



Hand-book of Perspective. By Henry A. James, B.A. 

 Cantab. (London : Chapman and Hall, 1888.) 



This small book contains the principles of perspective 

 explained in a plain and concise way. The author seems 

 to have taken great trouble to make his meaning as clear 

 as possible, and has spared no pains in getting together 

 a good collection of examples, which are all worked out 

 and accompanied in each case by a diagram. 



The examples themselves would form a useful and 

 practical course on the subject, since they are arranged 

 in a progressive order, starting with the projection of a 

 single point, and taking up in turn lines, surfaces, and 

 solids. 



Beginners will find this volume very serviceable to 

 them, pictures as well as diagrams being given to illus- 

 trate the various positions of planes, lines, &c. 



LETTERS TO THE EDITOR. 



[Tie Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he under- 

 take to return, or to correspond with the writers of, 

 rejected manuscripts intended for this or any other part 

 of Nature. No notice is taken of anonymous communi- 

 cations. '\ 



Coral Formations. 



In the last paragraph of my letter which appeared in your 

 issue of the 15th inst. (p. 462), I remarked: — "It is quite 

 reasonable to suppose that the dead coral so dissolved in the 

 formation of lagoons is carried out as material for fresh coral 

 growths." 



Mr. T. Mellard Reade, in a letter on the same subject, dated 

 22nd inst. (p. 488), in criticizing the results published by Mr. 

 Ross's letter of the 15th (p. 462), remarks: — " I believe that at no 



place on the surface of the globe are such dead shells being sup- 

 plied at a rate that would even balance this supposed rate of 

 chemical destruction." 



Can Mr. Reade give any observations or figures in support of 

 his view of the rate of accumulation of oceanic calcareous 

 deposits ? 



Laying aside all question as to arithmetical error, and without 

 committing myself to the accuracy of Mr. Ross's figures (or even 

 insisting on my own), as to the amount of dead carbonate of 

 lime dissolved in any given time by sea-water in lagoon forma- 

 mation, but taking it as a fact that it is soluble in a marked 

 degree (as is proved by the experiments made by Mr. Ross and 

 myself), and that coral reefs can only exist in regions under the 

 influence of the great warm tropical ocean currents, then we 

 may expect the waters of coral-bearing regions to contain a 

 greater proportion of lime than is found elsewhere, thus forming 

 the calcareous food for continuous extension of the coral forma- 

 tions. 



Of course, a distinction must be drawn between the so-called 

 dead and living coral, in thus far that the latter is protected from 

 the solvent action of the sea- water by its vitality, while the 

 former, as referred to in my last letter, is peculiarly susceptible to 

 this influence. Robert Irvine. 



Royston, Edinburgh, March 26. 



Professor Rosenbusch's Work on Petrology. 



Readers of Nature interested in the study of petrology will 

 be grateful to Dr. Hatch for his lucid review of Rosenbusch's 

 great work, and those who are not able to profit directly by the 

 German original will be glad of the rhumt given of the latest 

 classification of the massive rocks according to the views of the 

 greatest living authority on the subject. 



A translation of Rosenbusch's book into English is much to be 

 desired. Rich as we are in fragmentary literature on the 

 subject, a leading text-book is still wanting. Dr. Hatch would 

 deserve well of his fellow petrologists if he would give them a 

 translation of the work he reviews so well. There might be 

 room for some cutting down in dimensions, especially in the 

 treatment of the ' ' neo- volcanic " rocks. Rosenbusch himself is 

 conscious that this part of the work is, perhaps, a little over- 

 loaded with detail, as he says that with a new structure "the 

 scaffolding is not removed before the house is finished," and 

 possibly a competent translator might consider that a little less 

 scaffolding would still be sufficient. 



There will no doubt be more or less difference of opinion 

 among authorities as to the correctness of the views which have 

 governed Rosenbusch in his system of rock-classification, es- 

 pecially on one or two points. But none will deny that this 

 classification, with the immense research and study accompanying 

 and supporting it, fully given to the student in this latest work, 

 are a splendid achievement. 



Dr. Hatch does well, especially in the interest of younger 

 workers in petrology, to insist on the purely arbitrary nature of 

 any system of classification, so far as the separate "rock-types " 

 are concerned ; such types passing more or less gradually into 

 others, on either side of them, in all cases. Rosenbusch him- 

 self points this out, but a further emphasis of the warning was 

 well in place. 



In working with a large text-book like the one in question, 

 with its minute treatment of small details, the student is apt 

 to neglect this consideration of the passage of one rock into 

 another, or at any rate to devote too little attention to it. 

 Nothing, however, could be a greater safeguard to him in this 

 respect than to make for himself a tabular arrangement of Rosen- 

 busch's system, so that the eye can follow in a moment the 

 relationships of the different rock-types to each other. I think 

 it is a pity that such a map, as it were, does not accompany the 

 book. The attentive study of it would not only much assist the 

 worker in his detailed use of the book, but would also greatly 

 aid the beginner to "keep his head level " and steer clear of the 

 sad pitfall of going in too much for "pigeon-holes." 



Perhaps an outline table of this sort, which I inclose, may be 

 of a little use to some of your readers, if only to give a compact 

 view of Rosenbusch's classification and of how he connects the 

 main rock-types in series through the four divisions of plutonic 

 rocks, dyke-rocks, palaeo-volcanic rocks, and neo-volcanic 

 rock. 



An amplified table on the same model, with the various 



