NA TURE 



\May 3, 1877 



panied. The comets of short period — a most interesting 

 class — might well have been treated in somewhat greater 

 detail, and in this division of the work we note several 

 oversights. Thus it is stated that the researches of Dr. 

 Axel Moller upon the motion of Faye's Comet, show that 

 that body sujiports the theory of a resisting medium, first 

 supposed to be indicated by Encke's investigations relat- 

 ing to the comet which bears his name ; but as long since 

 as the year 1S65 Dr. Axel Moller had relinquished this 

 idea, and from a rigorous discussion of the observations 

 at the first three appearances, alluded to by M. Guillemin, 

 had succeeded in representing the observations by the 

 simple application of the planetary perturbations, with- 

 out any hypothesis whatever, and his later researches 

 have also negatived the existence of any trace of the 

 effect of a resisting medium upon the motion of this 

 comet. There is some ambiguity in the definition of the 

 element u, or the longitude of the perihehon in the orbit 

 of a comet ; from the explanation given by M. Guillemin 

 it might lather be inferred that the longitude is reduced 

 to the ecliptic, which is not the case. The comet dis- 

 covered by De Vicoat Rome, February 20, 1S46, is dupli- 

 cated, appearing first on p. 140 with a revolution of fifty- 

 five years, and again en p. 143 with a period of seventy- 

 three years ; the former period resulted from one of the 

 earlier calculations. Pigotl's comet of 1783 is named 

 amongst the contents of a chapter p. 133, but there is no 

 further reference to it. In the catalogue of orbits, there 

 are several cases since the year 1S66 where the inclina- 

 tion has been reckoned overgo", as is frequently the case 

 amongst the German computers, and with the unnecessary 

 addition of the letter R in the column headed "direction 

 of motion." To render these orbits consistent with the 

 method hitherto in general use, and indeed adopted 

 exclusively in the preceding part of the catalogue, the 

 inclination jiven requires to be subtracted from iSo', and 

 for the longitude of perihelion given in the fourth column, 

 2 a — TT, should be substituted. 



These, however, are small defects which may easily be 

 avoided in a future edition. As a whole, M. Guillemin's 

 "World of Comets "must prove a welcome aid to the 

 student on entering upon this branch of astronomy. 



J. R. HlXD 



OUR BOOK SHELF 



Foivncs's Inorganic Chcmistiy. Edited by Henry Watts, 



B.A., F.R.S. Twelfth Edition. (London : Churchills.) 

 In the present edition of this well-known manual the 

 publishers have, wisely as we think, determined to divide 

 it into two parts. In its old form the work had grown to 

 be as unhandsome and cumbersome a volume as could 

 be well imagined ; like an overgrown yeast-cell it was 

 obviously getting too big to hold together much longer, 

 and many a student on his way to and from the lecture- 

 room must have wondered, as he struggled to get the 

 thick squat book into a comfortable carrying position, 

 why ihe process of gemmation was so long delayed. 



The present volume, which treats of ph)sical and inor- 

 ganic chemistry, contains a considerable amount of new 

 matter, and may be regarded as an accurate representation 

 of the present state of knowledge on these subjects. Among 

 the more important additions we may mention an account 

 ofMendeleerVs Laws of reriodicity,'anda very good digest 

 of what is known concerning the new metal gallium 

 and its compounds ; this clement is associated with 

 indium, with the probable atomic weight 68, as already 



indicated by M. Mendeleeff. The position of the cerite 

 metals is also determined in accordance with the specific- 

 heat estimations recently made by Hillebrand. On the 

 other hand, it may be doubted if iodine tetrachloride has 

 any real existence, and Michaelis has proved that the 

 reaction 3PbS0, + 2POCI:; = 3S02CI.^ -f PbgP.Oj is not 

 realised in practice. On the whole, however, the work 

 fully maintains its reputation as a faithful exponent of 

 the state of contemporary chemical knowledge. T. 



The Microscopist : a Manual of Microscopy and Conipen- 

 diuni of the Microscopic Sciences. Third edition. By 

 J. H. Wythe, A.M., M.D. (London : Churchill, 1877.) 

 It is now some twenty-five years since the first edition of 

 this work appeared, and as the author himself remarks in 

 his Preface, it is no small compliment to a work of this 

 kind that for so many years it should hold a place among 

 works of reference, although surrounded by larger and 

 more pretentious volumes. For this third edition the 

 book has been entirely rewritten, the advancement of mi- 

 croscopical science having naturally rendered consider- 

 able enlargements necessary. Still the work retains its 

 principal qualities as before, viz., the precise and clear 

 language, the absence of all unnecessary verbiage, and 

 last but not least, the excellent arrangement of the con- 

 tents. Thus after a brief reference to the history and 

 importance of microscopy, we have able descriptions of 

 the microscope itself and its accessories, followed by 

 general remarks on its use and the more modern methods 

 of microscopic investigation. Then, after a short chapter 

 on the mounting and preserving of objects, we come to 

 well-written and richly illustrated treatises on the appli- 

 cation of the instrument in the difl'erent sciences, each 

 science being spoken of in turn and in a separate chapter. 

 For the beginner this arrangement is of special value, as 

 it enables him quickly to form a general idea of the whole 

 domain of microscopy. Mineralogy and Geology are 

 followed by a chapter on Microscopic Chemistry ; then 

 the author treats of Microscopic Biology, devoting a 

 chapter to Vegetable Histology and Botany, one to Zoo- 

 logy, the next to Animal Histology, and the last to 

 Practical Medicine and Pathology. 



The illustrations are original to a great extent ; many 

 also are taken from the works of Carpenter, Frey, 

 Strieker, Billroth, and Rindtleisch. The larger plates, of 

 which there arc twenty-seven, are particularly well drawn, 

 and add greatly to the general excellence of the work. 



LETTERS TO THE EDITOR 



[T/ie Editor does not hold Jiimsdf responsible for opinio)ts expressed 

 by his correspondents. Neither can lie nndeita/;e to return, 

 or to eorreipond with tite writers of, rejected manuscripts. 

 No notice is talcen of anonyjuons commutiicatioiis. 



The Editor urgently requests correspo7idents to kap their letters as 

 sliott as posiible. The presnire on his space is so great that it 

 is impossible otherwise to ensure the appearance eviti of com- 

 munications containing interesting and novel facts.] 



Hog-Wallows and Prairie Mounds 

 Judging from the desciiptions of these deposits, they must 

 be nearly, if not quite, identical widi ihose which I described in a 

 paper on " The Ancient Glaciers North and East of Llangollen," 

 read at the British Association, 1S65. These are a series of 

 heaps of glacial drift covering more or less completely the 

 habitat of Cheshire Cheese, i.e, the Vale Royal itself, and the 

 slopes which extend from it to those Welsh Mountains that are 

 so piominently seen from Chester. These mounds vary in size 

 and shape according to their posiiion. They are very well- 

 defined and numerous in the valley of the Alyn, between Wrex- 

 ham and Mold, where they have the form of oblong hog-back 

 mounds usually lying parallel to each other with their longer 

 axes (if I may use the term) nearly at right angles to the general 

 slope of the surface. They may be counted by hundreds, and in 

 some pavts are so near together as to form a series of connected 

 undulations. They are largest and most abundant upposiie the 

 mouths of the lateral valleys opening into the m.iiii valley of the 



