April 21, 1892] 



NATURE 



579 



perature of the cooled column is erroneously stated to 

 be the temperature of the air. A little more detail, es- 

 pecially in connection with the suspension of the tube in 

 Chapman Jones's boiling-point apparatus, would have 

 been advisable. 



Bunsen's method of calibrating a eudiometer is given, 

 but none of the methods for utilizing the results to obtain 

 the volume at any point is mentioned. 



The indiscriminate use of both English and French 

 units throughout the book does not seem to have any 

 advantage ; indeed, to give the dimensions of a tube as 

 " I millimetre in bore, ... 8 inches in length," may be 

 practical enough, but it is hardly scientific. 



The meaning of expressions such as "water . . . 

 drawn back ... by the partial vacuum," " liquid " of 

 a given " gravity," " ammonia condensed in hydrochloric 

 acid," "the tension of aqueous vapour," might be con- 

 veyed in language free from objection. 



The book is almost free from typographical errors ; 

 only two were noticed. On p. 227, cadmium sulphate 

 is printed for cadmium sulphide, and the letter {a) 

 should be replaced by {b) at the foot of p. 349. 



The table of contents, referring to page and para- 

 graph, and the index are particularly complete. A useful 

 appendix giving results of typical analysis, constants 

 for calculating results, &c., is added, and a list of works 

 of reference is given in the introductions to the different 

 parts. The relative importance of different estimations is 

 indicated by difference in the type, and cross-references 

 are frequently introduced. These points alone go a long 

 way to indicate the pains taken by the authors to meet 

 the wants of the student. J. W. R. 



ASTRONOMY. 



Elementary Mathematical Astronomy. By C. W. C. 

 Barlow and G. H. Bryan. " University Correspondence 

 College Tutorial Series." (London : W. B. Clive and 

 Co., 1892) 



THE task of writing a book on astronomy which shall 

 enable a beginner to grasp all the fundamental 

 principles and methods without entering into elaborate 

 details of mathematics is by no means a light one. What 

 the authors have done, and we may say very successfully 

 too, has been to strike a mean between the numerous non- 

 mathematical works and those which involve high mathe- 

 matics, using just enough to enable the reader, if he 

 wishes, to proceed to the more advanced treatises. 



To simplify matters further, all investigations which 

 require a knowledge of the elements of dynamics have 

 been collated together at the end under the title of 

 dynamical astronomy, thus separating them from those 

 of descriptive astronomy, which only needs elementary 

 geometry, trigonometry, and algebra. Some of the chief 

 properties of the eUipse which are of astronomical im- 

 portance are contained in the appendix, while for the 

 properties of the sphere an introductory chapter has been 

 inserted. 



This summary will give an idea of the range over 

 which the student will have to extend his mathematical 

 abilities, and after all it is by no means an extensive one, 

 considering the ground which this work covers. 

 NO. I 173, VOL. 45] 



In the chapter on the Observatory a very good account 

 is given of the transit circle and its accompanying errors ; 

 but of course, without spherical trigonometry, many points 

 of great importance with regard to the reduction of ob- 

 servations have had to be omitted. The chapters on the 

 earth, sun's apparent motion and time, all contain lucid 

 and concise explanations, which are well illustrated by 

 figures showing the great circles involved. Many in- 

 teresting problems are worked out in the chapters on the 

 moon and eclipses, while that on the planets contains a 

 good account of the stationary points in their apparent 

 motion. 



" The Distances of the Sun and Stars " is the title of the 

 chapter that concludes the non-dynamical section, and in 

 it the interesting problems on finding the parallax of the 

 sun are discussed, together with the various results that 

 ensue from the aberration of light. 



Coming now to the second part of the book, the rota- 

 tion of the earth and the resulting consequences are first 

 dealt with, in which the proofs of the former are clearly 

 described ; while many problems relating to pendulum 

 oscillations, variation of gravity at different places, «S:c., 

 are fully expounded. The following two and concluding 

 chapters are devoted wholly to the laws of universal 

 gravitation, and to the multiple applications to which 

 they are subjected. These chapters are perhaps the 

 best in the volume, and contain, of course, some most 

 important problems, such as the determination of the 

 density of the earth, precession, tides, &c. 



The examples and examination-papers, which are by 

 no means few in number, will be found to be both ori- 

 ginal and well selected ; and this is really important, for 

 a sound knowledge of this subject can be obtained only 

 by the continual practice of working them out. 



In conclusion, we may state that altogether the work 

 is one that is sure to find favour with students of astro- 

 nomy, and will be found useful to those for whom it is 

 especially intended. This is by no means the first 

 volume that we have received which is published in this 

 Tutorial Series, and the present work is a good example 

 of the excellent text-books of which it is composed. 



OUR BOOK SHELF. 



Practical Fruit Culture. By J. Cheal, F.R.H.S., 

 Member of Fruit Committee, Royal Horticultural 

 Society, &c. Illustrated. (London : George Bell and 

 Sons, 1892.) 



Within the last few years farmers and others have 

 often been advised to take to the cultivation of fruit, and 

 there can be little doubt that much of the profit con- 

 nected with fruit-growing — now absorbed by foreign 

 traders— might, under certain conditions, be kept in the 

 hands of our own people. The most important of these 

 conditions is that persons who think of devoting attention 

 to fruit culture shall obtain sound information about the 

 work they propose to undertake, and that at all the later 

 stages of their enterprise they shall act under the guidance 

 of trustworthy authorities. ' In the present Httle volume, 

 which forms one of Bell's " Agricultural Series," Mr. Cheal 

 has brought together, and carefully arranged, a great 

 many facts which cannot fail to be of service to intelligent 

 fruit-growers. He begins with a chapter on the general 

 prospects of culture for profit. Then come chapters on 

 the selection of soil and situation, the preparation of the 



