588 



NATURE 



\0ct. 1 8, 1888 



papers of various kinds. The author's language is very 

 inexact if compared with the language of Thomson and 

 Tait's " Natural Philosophy," or Dr. Lodge's text-book. 

 It reads as if a shorthand-writer had taken notes of 

 lectures, and the lecturer had published them after 

 hasty correction. This inexactness is visible in almost 

 every definition in the book. We read of velocities 

 acting and accelerations working. New magnitudes are 

 introduced ; thus, " the intensity of a force is like the 

 temperature of a body. It is measured by the velocity 

 communicated, apart altogether from the mass to which it 

 is communicated." " But the quantity of a force is like 

 the amount of heat in a body. Force-quantity is measured 

 by the product of the velocity communicated and the 

 mass to which it is communicated" (p. 103). In defining, 

 if he can be said to define, " impressed force," the author 

 uses expressions such as " so that when we speak or read 

 of an accelerating force,/ or g, or 9/8 or 32*2, or a per 

 second per second." 



This book would certainly not be recommended by us 

 to any student who is desirous of obtaining a know- 

 ledge of mechanics ; but, for all we know, it may 

 very well serve the purpose for which its author has 

 designed it. It is a book written for candidates in certain 

 examinations by a successful candidate. The author has 

 introduced side lines to catch a student's eye, and we 

 think this a very clever contrivance. Thus there is the 

 side line " Pressure " (p. 2), and the student is directed to 

 get off by memory : " When a body is prevented from 

 falling towards the earth by the hand or by a table, e.g., 

 the body exerts a certain pressure upon the hand or the 

 table." It is interesting to know from such an authority 

 as Dr. AveKng that this is the sort of definition which 

 satisfies an examiner, and it seems to us that a study of 

 this book by examiners would lead to very useful results. 



Solutions of the Examples in an Elementary Treatise 

 on Conic Sections. By Charles Smith, M.A. (London : 

 Macmillan, 1888.) 



Mr. Smith has been well advised in drawing up this col- 

 lection of elegant solutions to the examples in his 

 " Conies." His treatise is just now in the full tide of suc- 

 cess, and seems likely to maintain its position for some 

 time yet before a better one drives it into the background. 

 This, then, is just the time when such aid as is here fur- 

 nished is most acceptable to teachers, " many of whom," 

 as we have more than once stated in these columns, and 

 as the author here testifies, " can ill afford time to write 

 out detailed solutions of the questions which prove too 

 difficult for their pupils." We have compared many of 

 the solutions here given with our own (in manuscript), and 

 find that new light is thrown on some by Mr. Smith's 

 thorough command of the latest methods. We have 

 detected here and there a trifling error, which may per- 

 haps cause momentary trouble to a self-taught student, 

 but there is sufficient detail given to enable the reader, 

 on careful perusal, to make the required correction. In 

 some cases more than one solution is given : this is a 

 good feature. The possessor of the text-book and of the 

 "Solutions" occupies a strong position, and should be 

 able to attain considerable skill in this particular branch 

 of mathematics. 



The Beginner's Guide to Photography. By a Fellow of 

 the Chemical Society. (London: Perken, Son, and 

 Rayment, 1888. 



This is a second edition, revised and enlarged, of an 

 elementary guide for those commencing the art of photo- 

 graphy. In it will be found practical hints as regards 

 the choice of apparatus, and a good explanation of the 

 whole process of photographic manipulation, written in 

 a manner which for beginners leaves nothing to be 

 desired. 



An article on "Exposure" has been added by Mr. H . 



S. Platts, including tables and directions, and the latter, 

 if carried out by the amateur, ought to give him good 

 results. • 



There are, also, chapters on the production of lantern- 

 slides, enlarging, and photomicrography, and the book 

 concludes with a collection of the illustrations referred to 

 in it. . 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions 

 expressed by his correspondents. Neither can he nnder- 

 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. ] 



Prophetic Germs. 

 In his letter of October 8, the Duke of Argyll says that he 

 sees great value in my statement (which he improperly terms an 

 "admission"), that natural selection cannot act upon any 

 structure which is not already developed up to the stage of actual 

 use. He says, " This is really all I want for my previous argu- 

 ment, because all organs whatever do actually pass through rudi- 

 mentary stages in which actual use is impossible." Here we 

 have the Duke's case in a nutshell. It is easily dealt with. 

 Firstly, what the Duke terms an " admission " on my part is an 

 essential and explicitly stated element of Mr. Darwin's own 

 exposition of his theory. Secondly, it is necessary for the Duke 

 to demonstrate not that "all organs whatever," but that some 

 organs " do actually pass through rudimentary stages in which 

 actual use is impossible." 



The stages here alluded to are — if I understand correctly — 

 ancestral stages, not stages in the embryological development of 

 the individual. 



I feel bound to state that I do not know of any facts in the 

 history of either animals or plants which lead me (or, I may say, 

 which have led any important number of the vast army of writers 

 and observers on these subjects) to the conclusion that any exist- 

 ing active organ has passed through rudimentary stages in which 

 actual use is impossible, if we set aside such cases as may be 

 explained by correlation of growth or by the persistence of 

 vestiges of formerly useful structures. 



If the Duke of Argyll can show that any one organ has or 

 "must have" passed through such useless stages (not explicable 

 as due to correlation of growth nor as inherited vestiges), he 

 ought at once to do so. Mr. Darwin, in his severe testing of his 

 own theory, tried to find such cases, and did not find them. What 

 are they ? My own opinion is that they do not exist, and that the 

 Duke's case collapses. E. Ray Lankester. 



A New Australian Mammal. 



A few days ago, through the kindness of Mr. A. Molineux, 

 of Adelaide, a small mole-like animal, which appears to be 

 new to science, was forwarded to the South Australian Museum. 

 It was found on the Idracowie cattle-station, at a distance, I 

 understand, of about 100 miles from the Charlotte Waters 

 Telegraph Station, on the overland line from Adelaide to Port 

 Darwin ; but the exact circumstances of its capture are not yet 

 to hand. The collector, however, reports that it must be of 

 rare occurrence, as, on questioning the aboriginals of the locality, 

 there was only one old woman who said she had seen it before, 

 and that upon a single occasion. 



It is evidently an underground burrowing animal resembling 

 somewhat the Cape mole (Chrysochloris) in its general external 

 appearance, »but differing in many respects. 



The total length is 13 cm., inclusive of the tail, which is 2 cm. 

 long. The head, relatively shorter than Chrysochloris, has a 

 rounded muzzle, the dorsal surface of which is covered by a 

 horny shield. Nostrils transversely slit-like. No eyes visible, 

 the skin passing uninterruptedly over the ocular region ; but on 

 reflecting the skin on one side of the face a small circular pig- 

 ment spot is visible in the position of the eye. No apparent 

 bony orbit. Tongue fleshy, broad at the base, and tapering to 

 a blunt point. No external ears ; but the ear-openings distinct, 

 1 mm. wide, and covered over with fur. 



The fore-limbs are short, resembling somewhat those of a 

 mole; but the manus is folded, so that the large nails of the 

 fourth and fifth digits only are visible in the natural position of 



