142 



NATURE 



{Dec. 20, 1877 



instance L. 39836, a star which Lalande considered a sixth 

 magnitude. 



Different views will be taken with regard to the proper 

 contents of a celestial atlas, intended for general use, and 

 it is not nerefore desirable to be too critical upon this 

 point, but to take, we will say, two'extreme uses to which 

 an atlas of the pretensions of Dien's may be applied, first 

 for following a small planet with the aid of a chart pro- 

 fessing to contain stars to a less degree of brightness, and 

 secondly, for identifying the naked-eye stars by the 

 general maps including only these brighter stars, an 

 elementary purpose for which an atlas may be quite as 

 readily adapted as a globe. In the former case Dien's 

 maps are not sufficiently filled in to allow of a planet 

 equaUing in brightness stars of Bessel's ninth magnitude 

 being identified without some trouble and disappointment, 

 and in the latter case we meet with a failing which is only 

 too common with star- atlases — the outlines of constella- 

 tions are so prominently drawn as seriously to interfere 

 with, if not entirely to obliterate the naked-eye stars of 

 the lower magnitudes, in using the " Atlas " in the open air. 

 As a model of what an atlas should be in the latter 

 respect, we must still refer to Argelander's " Uranometria," 

 which, in our opinion, has yet no equal for the more 

 elementary uses of such a work. 



Among the best features in the new edition of Dien's 

 " Atlas " are the delineation of the southern heavens, in 

 which Brisbane's stars are laid down, the view of the dis- 

 tribution of double and multiple stars by M. Flammarion, 

 the orbits of some of the principle revolving double-stars, 

 and figures of remarkable nebulae and clusters of stars, 



OUR BOOK SHELF 



Horticulture. By F. W. Burbidge. With Illustrations. 

 (London: E. Stanford, 1877.) 



This is one of the series of small handbooks on the British 

 maufacturing industries, edited by Mr. G. Phillips Bev;\n, 

 of which we have already noticed several volumes, A 

 compact work on practical gardening, to serve as a guide 

 to the amateur gardener and fruit-grower, was much 

 wanted, and this volume to a certain extent supplies the 

 desideratum. After a short chapter on commercial garden- 

 ing, the author treats of the cultivation of fruit, and of the 

 various descriptions of vegetables and herbs ; and then 

 of gardening in its various departments, but more from 

 the economical than from the amateui^'s point of view. 

 If the owner of a garden wants to turn his bit of land 

 to the most profitable account, he will find Mr, Burbidge 

 an admirable guide ; but if he infers from the title of the 

 book that he will obtain from it advice as to the treatment 

 of his pelargoniums, fuchsias, and chrysanthemums, or 

 the management of his hothouses, he will be disappointed. 

 We fancy that information of this kind would commend 

 itself to a larger number of readers than the guide-book 

 information of the exact number of acres in each of our 

 London parks, and the annual cost of maintaining them. 

 The advice as to the culture of fruit and vegetables seems 

 to us very good ; but the rather poor woodcuts do not 

 add to the value of the volume. 



Mittheilungen aus dem k. zoologischen Museum su 

 Dresden. Herausgegeben mit Unterstiitzung der Gene- 

 ral-direction der koniglichen Sammlungen fiir Kunst 

 nnd Wissenschaft, von Dr, A, B, Meyer, Director des 

 konighcben zoologischen Museums. Zweites Heft mit 

 Tafel. (Dresden, 1877.) 



In a former volume of Nature (vol. xiii.,p. 464) we have 



given some account of the origin of this meritorious work, 

 of which the second portion is now before us. Like the 

 former half of the first volume of the contributions the 

 present section is chiefly occupied with memoirs based upon 

 the collections made by Dr, A, B. Meyer during his well- 

 known expedition to New Guinea and the adjacent islands. 

 Herr Th, Kirsch, the entomologist of the Dresden Mu- 

 seum, commences with two articles upon the lepidoptera 

 and beetles collected by Dr. Meyer in New Guinea. Of 

 the former Herr Kirsch enumerates 167 species, of which 

 133 belong to the diurnal section. Several novelties are 

 described and well figured. The next article is by Dr. 

 Meyer himself, and gives us an account of a large series of 

 Papuan skulls which he collected on the mainland of New 

 Guinea and in the Island of Mysore, in the Bay of Geeldink. 

 The collection, embracing altogether 135 examples, is, 

 we believe, by far the finest of this branch of the human 

 family ever made, and should, we suppose, lead to some 

 definite results upon that somewhat mysterious subject — 

 the differentiation of the various races of mankind by their 

 skulls. A second article by Dr. Meyer relates to the speci- 

 mens of anthropoid apes in the Dresden Museum. We 

 cannot say that the photographic plates of the stuffed speci- 

 mens of these creatures are either elegant or likely to be of 

 very great use, butitis.'satisfactory tohave the vexed ques- 

 tion of the identity of the celebrated '"' Mafoka " lately living 

 in the Zoological Gardens at Dresden, and long supposed to 

 be a gorilla, finally set at rest, as is done by von Bischoff's 

 article on its anatomy, which follows that of Dr. Meyer. 

 A memoir on the Hexactinellid Sponges collected by Dr. 

 Meyer in the Philippine Seas, in the preparation of which 

 Herr W. Marshall has given his assistance, concludes 

 this interesting volume, of which we may say that it adds 

 materially to the status of the Dresden Museum, and to 

 the scientific fame of its energetic director. 



LETTERS TO THE EDITOR 



[The Editor does not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he undertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken of anonymous communications. 



The Eddor 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 atui novel facts. ^ 



The Radiometer and its Lessons 



I AM obliged to ask you to allow me to add a few words, by 

 way of further explanation, to my letter printed in Nature, 

 vol. xvii. p. 80. 



In trying to estimate the effect of the communication of heat 

 between a solid body and contiguous gas, I have assumed that 

 certain simplifying suppositions may be legitimately made, for 

 the most patt identical with what are very commonly adopted in 

 discussing the pressure exerted by a gas on a solid in contact 

 with it. That is to say, I have assumed, first, that we may 

 resolve the velocities of the mjlecules of gas into three rectangu- 

 lar components, one perpendicular to the surface of the soiid 

 and the other two parallel to it ; second, that we may conceive 

 of the who!e number of molecules as divided into three equal 

 parts, one- third moving in the direction of each of the resolved 

 components of the velocity respectively ; third, that the mutual 

 pressure between the solid and the gas, and any communication 

 of heat from one to the other, may, for the purpose in 

 hand, be attributed to direct impacts of molecules against 

 the solid surface ; fourth, that all the molecules endowed 

 with a velocity perpendicular to the solid surface, and con- 

 tained within a layer adjacent to this suiface of a thickness 

 not greater than the mean length of path, will strike the surface, 

 while none of those which are outside this layer will ever reach 

 it ; fifth, that the particles which have struck the solid surface 

 will return from it with an average velocity corresponding to the 

 temperature of the surface, and will retain this velocity until 

 they arrive at the farther side of the layer before- mentioned. It 

 was on the supposition that these are legitimate assumptions that 



