52 



NA TURE 



[November 19, 189] 



executed with that clearness and finish for which so many 

 Continental scientific works are justly to be commended. 

 To give an idea of its contents it will be sufficient to 

 mention the headings of the sections, viz. apparatus for 

 the negative process, photographic objectives, instan- 

 taneous shutters, portable cameras, equipment of the 

 dark room, general remarks on exposure, negative 

 processes, positive processes, cyanotype and similar 

 processes. The work, as its title implies, is purely 

 technical, and, as such, does not call for lengthened 

 notice in these columns, but for the particular object with 

 which it has been written it is admirably adapted, and 

 should find many readers in this country. We have 

 nothing which can be compared with it for conciseness 

 and completeness. 



An Introduction to the Differetitial and Integral Cal- 

 culus. By T. Hugh Miller. (London: Percival and 

 ♦ Co., 1891.) 



This small book contains a fair amount of the calculus 

 put together in a clear and readable form. It merely 

 touches the subject, but appears to contain enough to 

 meet the wants of a South Kensington examinee. " It 

 assumes a knowledge of elementary algebra and trigono- 

 metry as far as the properties of plane triangles." The 

 student is supposed to be unacquainted with analytical 

 geometry, but as he is credited with a knowledge of the 

 exponential and binomial theorems, with " indeterminate 

 coefficients" and a few other matters, it will be seen 

 that elementary includes a fair grasp of the two subjects 

 named. Six chapters are devoted to the elements, suc- 

 cessive differentiation, the theorems of Leibnitz, Taylor, 

 and Maclaurin, maxima and minima values of a function 

 of one variable, and the evaluation of indeterminate ex- 

 pressions ; the remaining four chapters are devoted to 

 elementary integration, formulae of reduction, rational 

 fractions, and a few applications of the integral calculus. 

 We presume that the miscellaneous examples are taken 

 from South Kensington papers ; those in the text are old 

 friends which figure in Todhunter's works. In the text, 

 the following slips occur : p. 4, 1. 15, for /(a) read/'(.t-) ; 



X T-O ^Jj 



p. 18 (6), reade"" ; p. 37 (3), for -^— we get — ; p. 40 



720 5 



(3)) ? (« - bYla for the maximum ; p. 41, 1. 4 up, for 2^4-3^, 

 read 3^ + 2^ ; p. 42 (i), read cos^ 6 and 3 V3<^Vi6 ; p. 62 

 (4), ? last connecting sign (read - ) ; p. 71 (4), for tt read 

 TT^ ; p. 80 (24), in first place read {i-^x^Y. In the 

 answers, we differ from the author in (i), (20), (74), and 



(88). We prefer to work (84) from j {i+t^fdt, where t 



stands for tan x. 



Star Groups. By J. Ellard Gore. (London : Crosby 

 Lockwood and Son, 1891.) 



A KNOWLEDGE of the principal constellations visible in 

 our latitudes may be easily acquired from the thirty maps 

 and accompanying text contained in this work. All stars 

 down to the sixth magnitude are shown, and brief de- 

 scriptions given of the objects of interest in each constel- 

 lation. The maps are intended to be useful as an 

 introduction to larger atlases, and will doubtless serve 

 this purpose well ; but a beginner unacquainted with the 

 motions of the heavenly bodies will hardly find in them 

 what he requires. G. 



The Universal Atlas. (London : Cassell and Company, 

 1891.) 



This atlas is being issued in twenty-eight parts, including 

 the index, eight of which have already appeared. It con- 

 tains fifty-eight single page maps and thirty-two double 

 page, several illustrating physical geography. The maps 

 are well drawn and reproduced, and full of detail, whilst 



NO. 1 151, VOL, 45] 



their large scale has enabled the names of all places of 

 any importance to be printed with perfect legibility. In 

 fact, all who require a good atlas, for reference or other- 

 wise, would do well to obtain this one. G. 



La Transcaucasie et la Pdninsule d'ApcMron. Calouste 



S. Gulbenkian. (Paris: Hachette et Cie., 1891.) 

 This is a very pleasant book of travels, well worthy of 

 the attention of all who for any reason take interest in the 

 Caucasus. The author has no very stirring adventures to 

 tell us of, but he presents lucid and attractive descriptions 

 of the towns and districts through which he passed, and 

 of the manners and customs of the inhabitants. Especially 

 good are the chapters he has devoted to the petroleum 

 industry — chapters which have already appeared in the 

 Revue des Deux Mondes. He gives also a very interest- 

 ing account of Oriental carpets, the manufacture of which 

 plays so great a part in the Caucasus. 



How to Organize a Cruise on the Broads. By E. R. 



Suffling. (London: Jarrold and Sons, 1891.) 

 In preparing this little book, the author did not attempt 

 to provide a guide to the Broads. He intended the 

 volume to serve merely as a supplement or appendix to 

 the various guides already accessible. A cruise on the 

 Broads is heartily enjoyed by everyone who tries it under 

 tolerably favourable conditions, and certainly not least by 

 students of natural history. Anyone who may think of 

 making the experiment will find in Mr. Suffling's pages 

 all the information that is really necessary for the forma- 

 tion of suitable plans. In one chapter he presents a brief 

 and interesting diary of what may be looked for at the 

 Broads during the various months of the year. 



LETTERS TO THE EDITOR. 



[The Editor does not hold himself responsible for opinions ex- 

 pressed by his correspondents. Neither can he undertake 

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

 manuscripts intended for this or any other part of I^^ATVKK. 

 No notice is taken of anonymous communications.^ 



A Difficulty in Weismannism. 



I HAD intended to accept Prof. Hartog's challenge, and say a 

 few words on this subject at an earlier date, but absence from 

 home and many engagements have interfered until now. 



In some respects it would have been more convenient to defer 

 such a discussion until Weismann's last essay, "Amphimixis," 

 has become more widely known, or even until the appearance 

 of his complete and detailed work, which is expected some time 

 next year. Prof. Weismann tells me that the points raised by 

 Prof. Hartog are considered in this treatise, and, such being 

 the case, he is unwilling to tax his already over-strained eye- 

 sight with any earlier reply. 



As the question has been raised, I will briefly speak of the 

 manner in which I have tried to see my way through such diffi- 

 culties. I do not, however, wish to involve anyone else in the 

 responsibility for the attempt, which is no doubt crude and 

 insufficiently thought out. 



Accepting Prof. Hartog's five theses as fair statements, I have 

 always proceeded to make his hypothesis B, and in this I 

 believe I am following Prof. Weismann. Hypothesis A had 

 never occurred to me, and I agree with Prof. Hartog in con- 

 sidering it as valueless But I believe a way through the difficul- 

 ties raised against hypothesis B may be found in the assumption 

 of a relationship between the Ahnenplasmas in the germ- 

 cell. Such a relationship is perhaps hinted at by Prof. Hartog 

 in Thesis IIL, where he speaks of these units as lying "asso- 

 ciated together," and in this respect the metaphor of two packs 

 of cards in Thesis IV. is, I believe, inadequate. I have always 

 been accustomed to regard the relationship between the ancestral 

 units, the " pattern " or figure which they form, as an essential 

 part of the process. I have regarded the units as the necessary 

 material, like the pigments in a colour-box, while their arrange- 



