126 



NATURE 



[Dec. 6, 1888 



sections. He also, in his desire to be abreast of current 

 literature, uses such terms as " allotriomorphic," "micro- 

 /elsitic," "magma-basalt," without adequate definition 01 

 discussion ; and in speaking of a " porphyritic ground- 

 mass " he will throw many beginners into confusion. If 

 the student is to seek elsewhere for instruction both in the 

 manipulation of the polariscope and in the use of technical 

 terms, the book must be held to fail in its fundamental 

 object as a primer. It will probably serve well, however, 

 to "remind the learner of the broader features that mark 

 out one rock-forming mineral from another. The author, 

 moreover, insists, as befits a geologist, on the purely 

 supplementary character of microscopic study^a warning 

 that seems more than ever needed when micro-petro- 

 graphy, hy the change of a few letters, has been exalted to 

 the level of a science. 



The statements in this book are essentially accurate, 

 and the illustrations, excepting that of ophitic structure, 

 may be useful in recalling diagrammatically what has 

 been seen in actual sections. On p. 32, however, there 

 is an incorrect account of the pleochroism of muscovite, 

 which probably has arisen from a blending of two 

 totally independent notes. On p. 36 the sections of augite 

 should be described as having, not six, but eight sides ; 

 and talc reappears on p. 50 as a constituent of protogine 

 granite. The cleavages in drawings on pp. 33 and 36 are 

 not in every case consistent with the descriptions. 



G. C. 



Theoretical Mechanics. By J. E. Taylor, M.A. (London : 



Longmans, Green, and Co., 1888.) 

 So long as examinations on. prescribed courses are in 

 vogue, so long, we suppose, will text-books be written for 

 them. The book before us has been prepared chiefly to 

 help those who are studying for the elementary stage of 

 the Science and Art Department's examination in the 

 subject, but it also covers the requirements for London 

 matriculation. There is not much scope for originality 

 in a work of this description, and in looking through it 

 we find ourselves in familiar, well-worn paths. 



In his preface, Mr. Taylor states that he has endeav- 

 oured to make the subject comprehensible to the beginner, 

 but we are afraid that his efforts to explain the difference 

 between mass and weight will be far from successful. 

 This is always a delicate point to touch upon, but we 

 venture to say that few beginners will be likely to under- 

 stand the explanation given on page 8. This is as 

 follows : — " Whilst mass is always measured by weight, 

 yet the two terms must be kept distinct, the weight being 

 the amount of force which the attraction of the earth 

 e.Kcrts on the mass. If g represent this attraction, 

 W, weight of the body, ;//, mass, we have W = nigT 

 Most beginners are likely to imagine from this that W 

 should be equal to g, instead of to mg. 



The book is well illustrated throughout with many new 

 diagrams and several old ones from well-known text- 

 books. Numerous examples, worked and unworked, 

 are also given. 



With the exception referred to, the book is on the 

 whole well written, and completely covers the Syllabus. 

 The admirable style in which it has been issued, and 

 its comparative cheapness, will commend it to many 

 teachers. 



Instructions for Observing Clouds on Land and Sea. By 

 the Hon. R. Abercromby. With Photographs and 

 Engravings. 22 pp. (London: Stanford, 1888.) 

 The phrase Nascitur no7t fit may be applied to cloud 

 observers with almost the same confidence as to poets ; at 

 least, such is the experience of most persons who have 

 attempted to teach an ordinary observer to record cloud 

 phenomena. 



Mr. Abercromby's pamphlet, however, contains a 

 valuable stock of instruction which may be placed in the 



hands of intending observers, and will at least indicate to 

 them what they have to observe. 



The actual nomenclature of cloud forms used by Mr. 

 Abercromby is that which has been, for the time at least,, 

 rejected by the International Committee at the recent 

 meeting at Zurich (Nature, vol. :!^xxviii. p. 491), but this 

 is a minor matter. The illustrations of cloud perspective 

 and cloud motion are new and good, while the difference 

 between the motion of advance, the " propagation " of a 

 cloud bank, and the rotation of the clouds within that 

 bank is, for the first time, clearly stated. The importance 

 of the R. point (radiation point), the point towards which 

 the stripes of cirrus converge, is explained. 

 Mr. Abercromby concludes as follows : — 

 " It (cloud observing) cannot be learnt in a day, but 

 with a little attention and practice the knowledge is soon 

 acquired. The observer, who begins by taking simple 

 cases of low, fast-moving clouds, till he has fully realized 

 the meaning and importance of R. points, will soon at- 

 tain such proficiency as will enable him to make valuable 

 observations in the most recent branches of modern cloud 

 science." 



Laboratory Manual of General Chemistry. By R. P. 

 Williams, A.M. (Boston : Ginn and Company, 1888.) 



After a few preliminary matters, including some good 

 rules for students in the laboratory, each two pages of 

 this book has in large type consecutive directions for 

 performing an experiment or exercise. The rest of the 

 two pages is left blank for written notes. One hundred 

 exercises are given, and they are of a quite elementary 

 character. It is a pity that contractions are so frequently 

 used, especially when there is a large amount of vacant 

 space and so small an amount of matter. " Ap. : p.t., 4 

 rec, t.t., d.t., r.s." indicates to the student the apparatus he 

 needs for the purpose of preparing hydrogen. It would 

 have been better to adopt a recognized system of short- 

 hand throughout, for that would have rendered the book 

 more useful to some and quite useless to others, instead 

 of troublesome to all. 



LETTERS TO THE EDITOR. 



{The Editor does not hold himselj 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 anonytnous communi- 

 cations. 1 



Mr. Romanes on the Origin of Species. 



What the Times said is substantially the same as what Mr. 

 Romanes himself says on p. 366 of his paper : ' ' The theory oi 

 natural selection is not, properly speaking, a theory of the origin 

 of species : it is a theory of the development of adaptive structures. 

 Only if species alwaj's differed from one another in respect of 

 adaptive structures, would natural selection be a theory of the 

 origin of species. But, as we have already seen, species do not 

 always, or even generally, thus differ from one another, " Very 

 well then, I say, if this be true, it shrivels up the part played by 

 natural selection to very small dimensions. 



The second part of Mr. Romanes's reply consists of a com- 

 plaint that when I quoted from his paper the words " natural 

 selection not a theory of the origin of species,'' I did not see that 

 they were " flatly falsified " by the section at the head of which 

 they stood. I do not see it even now, because the section 

 finishes with what Mr. Romanes oddly calls an " insinuation " 

 " that Mr. Dai win's great work on the ' Origin of Species' has 

 been misnamed." If this insinuation be just, then I further^ 

 do not understand how Mr. Darwin's reputation for candour i»| 

 to be saved except at the expense of his intelligence. 



In the third part of his reply, Mr. Roaianes says "he [Mr. 

 Dyer] must surely be aware that other l)otanists who have morel 

 thoroughly considered the subject are dead against him in hi9| 

 general conclusion." I have perhaps as many opportunities a;^| 

 most men of knowing the opinions of botanists, and I cannot ^ 



