July 2 2, 1880] 



NATURE 



26 = 



fossil genera then known in the several geological forma- 

 tions. This book, which ^vas accompanied by an excellent 

 atlas of plates, passed through three editions during the 

 author's Hfe-time, but in the preparation of the last of 

 these he was aided by Dr. Ferdinand Roemer. 



The number of fossirforms now known to geologists is 

 so vast that it would be impossible to find any pateonto- 

 logist competent to deal equally well with the faunas and 

 floras of all the geological periods ;" and hence it has been 

 decided to commit the pateozoic, the mcsozoic, and the 

 tertiary divisions of the work to different hands. Dr. 

 Ferd. Roemer has been selected to describe the life- 

 forms of the pateozoic rocks, and in the work before 

 us we have the first instalment of the result of his 

 labours. 



The work commences with a sketch of the succession 

 and correlation of the pateozoic strata in all the different 

 areas in which they have been studied. The author 

 divides these rocks into the four groups of Silurian, 

 Devonian, Carboniferous, and Permian, using the term 

 Silurian, after the manner of Murchison, to embrace all 

 the lower pateozoic strata. This plan is, of course, open 

 to the objection that his first division is at least equal in 

 value to the other three put together. The account of the 

 pateozoic strata as developed in different areas, which 

 extends to ninety-two pages, is generally very carefully 

 drawn up. We notice on pages 1 1 and 29 an unfortunate 

 error in the grouping together of the Lower Llandeilo 

 and the Tremadoc slates, while in his account of the 

 succession of strata in Sweden the author has failed to 

 avail himself of the most recently -published results arrived 

 at by the paleontologists of that country. 



The next twenty pages of the work are devoted to the 

 pateontological literature of the pateozoic rocks, 1 46 pages 

 to the pateozoic plants, and seventy-seven pages to the 

 Protozoa. The author describes each genus, and gives 

 also an account of some of the more important species. 

 In noticing the earliest pateozoic plants, Roemer follows 

 Schimper in regarding the puzzling forms from Bray Head, 

 called Oldhamia by Edward Forbes, as belonging to the 

 Algas. With regard to the so-called Eozoon canadcnse 

 of Dawson, Dr. Ferd. Roemer accepts the verdict of 

 Mobius against its organic origin, and rejects it from the 

 list of pateozoic fossils. 



The atlas of the " Lethaea Pateozoica " was published 

 four years ago, the plates, sixty-two in number, being 

 well executed and of the same size as the text, thus 

 getting rid of the inconvenient arrangement in the former 

 work, where the text was in Svo, and the plates in folio. It 

 would almost appear as if the atlas were drawn up pre- 

 vious to, and quite independently of, the present work, 

 so that the connection between the illustrations and the 

 text is not so close as might be wished. We cannot help 

 remarking, too, that unless much greater expedition is 

 used in publishing the remainder of the work, the earlier 

 portions will become obsolete before the later portions 

 make their appearance. 



Although the atlas appeared in 1S76, the text has now 

 only just reached the commencement of the Coelenterata. 

 Possibly some unavoidable cause of delay has arisen, 

 which, we may hope, is now removed. We look forward 

 with interest to the completion of this most valuable 

 work. 



OUR BOOK SHELF 



A Treatise on Elementary Dynamics, for the Use of 

 Colleges and Schools. By William Garnett, M.A. 

 Second Edition. (Cambridge : Deighton and Co., 

 1879.) 



Mr. Garxett's second edition does not differ in appear- 

 ance from its predecessor. There is the same number of 

 chapters, the headings of which for the most part are also 

 the same, but new matter and more detailed explanation 

 have resulted in the addition of some twenty-five pages. 

 It may be noted as a feature of Mr. Garnett's work that 

 there is a chapter on "The Dynamical Theory of Gases," 

 and a good one on "The Dimensions of Units." We 

 have used the first edition with great advantage, as the 

 author fully discusses and illustrates the criiccs of this 

 subject, which is often so difticult to beginners, and we 

 commend this improved edition to such readers and to 

 all others. 



Elementary Applied Mechanics. By Thomas Alexander, 



C.E. (London : Macmillan, 18S0.) 

 The object of Mr. Alexander's work is to serve as a com- 

 panion volume to the late Prof. Rankine's "Applied 

 Mechanics and Civil Engineering." Th.\sfrst part treats 

 of internal stress and strain, the divisions being elasticity, 

 resilience ; pure strain, simple and compound ; the ellipse 

 of stress ; and the application of earthwork. All these 

 points appear to us to be well illustrated by the numerous 

 worked-out exercises, with carefully drawn figures, and 

 by the exercises left for the student to try his skill upon. 

 This small book, drawn up, we presume, with reference 

 to Prof. Alexander's Japanese students at the Imperial 

 Engineering College at Tokei, is likely to be of service, 

 the more so as it appears, to the extent we have tried it, 

 to be correctly printed. 



LETTERS TO THE EDITOR 



]The Editor does not hold himself responsible for opinions expressed 

 by his correspondatts. Neither can he undertake to return, or 

 to correspond with the writers of, rejected manuscnpts. No 

 notice is taken of anonymous communications, 



[ The Editor urgently requests correspondents to keep their letters as 

 short as possible. The pressure on his space is so great that it 

 is impossible otherwise to ensure the appearance even of com- 

 munications containing interesting and novel facts.l 



The Recent Gas Explosion 



"The explosion took place by the conversion of potential energy 

 ijito incfion.^^ 



It may be fairly asked whether physicists are really satisfied 

 ■i\ith this account of the tremendous development of energy 

 recently ;\ itnessed in the neighbourhood, or whether this phrase 

 " potential energy " is not a useless bugbear which is closing the 

 door to discovei'y. Why not believe rather that the motion 

 exhibited was not really created (as motion) at all, but already 

 existed in a concealed form ? For we have plenty of proof that 

 motion can be stored up to any intensity and yet be quite im- 

 perceptible to the senses, so long as all is in equilibrium. Why 

 assume a supernatural (?) cause, when we have a natural one of 

 transferred motion ? Why rush into the inconceivable assumption 

 of the existence of an energy without motion, when the conceivable 

 remains for appreciation ? An important and highly interesting 

 problem in the discovery of the modus operandi of the transference 

 of the motion from matter in space would thus be ever present to 

 the mind (which is the sole condition for hoping to solve it) in 

 place of an unrealisable and — may we not justly add? — therefore 

 shallow and pretentious mysticism which obstructs the pathway 

 of progress. S. ToLVER Preston 



July S 



[It seems to us that Mr. Preston makes rather too much of a 

 chance newspaper expression, probably employed (for the sake 

 of appearing scientific) by a writer who had no notion of the 

 tremendous metaphysical problem which underlies it. It is very 

 probable that all energy is kinetic, but this has not yet been 

 proved.— Ed.] 



