March 1 8, 187 5 J 



NA TURE 



585 



have proved that we have sohd grounds for maintaining 

 that man, considered both in his psychical and his physical 

 nature, has been developed gradually and normally, and 

 must be regarded as a link in one and the same serial 

 chain of development to which all other organic bodies 

 belong. Furthermore, he asserts that we cannot regard 

 the organic and the inorganic as of heterogeneous origin ; 

 such an assumption would militate against the unity of 

 the universe ; and therefore we must assume that the 

 organic. has been developed from the inorganic. As deve- 

 lopment depends upon attraction and motion, and assimi- 

 lation regulates the combinations of atoms and molecules^ 

 the ultimate development of more highly organised bodies 

 is dependent upon the assimilation of more perfect com- 

 binations of matter, or, in other words, on better food, and 

 hence the striving of the animal nature to obtain definite 

 forms of nourishment must of necessity have exercised a 

 paramount influence on its higher development. Thus, he 

 argues that the organs of the senses, as sight, taste, &c., 

 resulting ultimately in the formation of brain and nerve 

 centres, have been developed in the vicinity of the mouth 

 as auxiliaries in the process of nutrition. The author 

 believes that every group of organisms has a definite 

 supreme beyond which it cannot ascend : and while he 

 considers that, mentally and psychically, the best of the 

 human race will probably in remote future ages be able to 

 attain a higher degree of perfection^ than any allotted to 

 us in the present age of the world, he does not anticipate 

 that externally they will differ greatly from ourselves. 



The difficulty of answering why animals no longer pass 

 the bounds of their parental types, he meets by assuming 

 that the cosmical, natural, and geognostic relations which 

 rendered such an advance possible in the case of the human 

 race, and of the forms from which it was directly deve- 

 loped, no longer exist, and that hence the lower animals 

 must remain fixed within their several limits. 



We do not know how far his German readers may 

 approve of the phonetic mode of spelling adopted by the 

 author, but we confess that, notwithstanding the high 

 authorities which its advocates advance in its justification, 

 we fail to recognise its expediency or desirableness, and 

 greatly prefer the ordinary mode. 



OUR BOOK SHELF 



The Aerial World: a Popular Account of the Pheno- 

 mena and Life of the Atmosplierc. By G. Hartwig, 

 M. and P. D. With eight Chromoxylographic Plates, 

 a Map, and numerous Woodcuts. (London : Long- 

 mans and Co., 1874.) 



Dr. Hartwig is already well known as one of the most 

 successful popularisers of the results of scientific research ; 

 and judged of from the point of view from which they 

 are written, his books must, we think, be reckoned as of 

 considerable value, and as likely to be of much use, both 

 in spreading accurate scientific information and in giving 

 their readers a taste for further independent study of 

 science. Under present conditions we deem works of 

 this class a perfectly fair means of scientific propa- 

 gandism, hopmg all the same that the time will come 

 when the gospel of science will need no allurements to 

 make it attractive to the people. In this volume Dr. 

 Hartwig gives a vast amount of information on a great 

 many subjects intimately or remotely connected with the 

 air. It is not merely a popular^ treatise on Meteorology, 



which of course has a large share of space devoted to it, 

 but it contains as well much information on Sound, Light, 

 Aerolites, Geology, Ocean Currents, Flight of Birds and 

 Insects, Aerostatics, and many other things in " the 

 heavens above, the earth beneath, and the waters under 

 the earth.'' All the information in the book is valuable 

 and rendered attractive mainly by a profusion of anec- 

 dotes, on the whole happily introduced. Dr. Hartwig's 

 style is fluent and generally agreeable, sometimes elo- 

 quent and occasionally florid. His information, collected 

 from a vast variety of sources, so far as we have tested 

 it, is accurate and well up to time. We sincerely wish 

 the work a large circulation. The numerous illustrations 

 add in the main to its attractions. 



LETTERS TO THE EDITOR 



[Tlie Editor docs not hold himself responsible for opinions expressed 

 by his correspondents. Neither can he ttndertake to return, 

 or to correspond with the writers of, rejected manuscripts. 

 No notice is taken oj anonymous communicaiions.] 



A Gyrostat Problem 



The following question, taken from an examination paper set 

 to the students of the Natural Philosophy Class in this Univer- 

 sity, .Sir \V. Thomson desires me to send to Nature, as one 

 likely to be interesting to its readers. 1 he answer will be sent 

 b.ter, when the examination is over : — 



"A gyrostat, hung by a cord CC at a distance of .six centi- 

 metres from its centre of gravity, keeps its axis B B horizontal 

 v.hen turning in azimuth at the rate of one- fourth of a radian * 

 per second. How many revolutions does the fly-wheel A A 

 make per second ? The weight of the wheel and case is 2,250 

 grammes, the mass of the wheel alone is 1,800 grammes, and 

 its radius of gyration is four centimetres." 



The University, Glasgow, March 13 D. M'Farlane 



* The term radian has been recently introduced by Prof. James Thomson 

 to denote the unit angle, that is, the angle subtended by an arc equal in 

 ength to the radium. 



