August i6, 1906] 



NA TURE 



379 



«ork is contrasttd with that of his ihree groat ron- 

 Imiijurarics, C'avfiidish, Schecle and Lavoisier. 



Oiir explanation of these defects may be found in 

 Ihr fan that he was not, as he said, "a practical 

 ilurnisl," or, as we should say, a trained chemist. 

 Ihis was perfectly true. That he Unew little .about 

 llie substances which he employed in his experiments 

 is evident from his habit of applying to his chemical 

 friends for such materials as a man like Scheele would 

 never have hesitated to prepare himself, and, more- 

 over, the absorbing interest of his laboratory seems to 

 h.ive obliterated any inclination towards the study of 

 tr\t-books. 



Priestley, in both his social and scientific life, seems 

 1(1 have been pursued by an ironical fate. On the 

 one hand his honest zeal in the cause of reform was 

 liirned against him to his undoing; on the other, his 

 r\|)eriments which were founded on his cherished 

 iheory of phlogiston became the weapon which demo- 

 lished it. Priestley was fortunately endowed with a 

 serene disposition, and in spite of his many misfor- 

 tunes it would be incorrect to suppose that his life was 

 not a source of real happiness and satisfaction. .Such 

 at least may be gathered from the perusal of the 

 volume before us. J- B. C. 



SrilHRICAI. ASTKOXUM Y. 

 A Conipeiidiuin of Splierical Astrojwwy with its 

 Appticiitions to the Determination and Reduction of 

 I'osilioiis of the Fixed Stars. By Prof. Simon 

 Newcomb. Pp. xviii-l-444. (London: Macmillan 

 and Co., Ltd., 1906.) Price 12.';. 6d. net. 



A.S Prof. Newcomb has been in close touch with all 

 branches of the astronomy of position during 

 the last fortv vears, and as so much of the progress 

 that has been made is his work, a text-book by him 

 on spherical astronomy will be eagerly examined by 

 .ill who are interested in the subject. 



With such qualifications we may be sure, before 

 opening his book, that we shall be conducted to the 

 various points on the frontiers of the subject, some of 

 u hich it is necessary to occupy before an advance can 

 be made in any direction ; and we are also certain 

 to be spared those tiresome digressions into problems 

 such as " To find the season of the year, when twilight 

 is shortest in a given latitude," which serve to 

 di-grade astronomy into a mere examination subject. 



Let us examine Prof. Newcomb's arrangements. 

 His first three chapters, forming part i., are intro- 

 ductory. They serve to equip the reader with a 

 competent knowledge of spherical trigonometry, inter- 

 linlation, and least squares. A pleasing feature at the 

 ( nd of each chapter is a page or two of bibliography. 



Part ii. opens with a chapter on spherical co- 

 ordinates. Practical illustration is given of the 

 problem, so simple in theory and so laborious in 

 practice, of turning latitude and longitude into right 

 ascension and declination; and here we find a striking 

 feature differentiating Prof. Newcomb's book from 

 oni- that would be written bv a mere lecturer on 

 NO. 1920, VOL. 74] 



astronomy. The lecturer, if he gave an example at 

 all, would probably work to the nearest tenth of a 

 degree with four-figure logarithms, and tell the 

 reader that that sufficiently illustrates the method. 

 Prof. Newcomb's book is for those who may want to 

 carry out actually calculations of the kind. He there- 

 fore places before the reader two different computa- 

 tions of the same problem each with seven-figure 

 logarithms, and knowing that the difficulty is the 

 practical one of keeping out numerical blunders, and 

 not in the last degree the theoretical one of under- 

 st.inding the formulae, he adds a test computation, 

 thus forcibly insisting upon the superior value ol 

 checks by test equations over checks by duplicate 

 computation. 



The fifth chapter of the book, the second of part ii., 

 is on time, solar and sidereal, mean and apparent, 

 Creenwich and local, the Besselian and Julian year, 

 with numerical examples. 



The sixth chapter is on par.illax, naturally sub- 

 divided into figure of the earth, and formulae for 

 parallax in right ascension and so on. 



The seventh chapter is a very short one on aberra- 

 tion. 



The next chapter is on refraction. "There is 

 perhaps," savs the author, " no branch of practical 

 astronomy on which so much has been written .... 

 and which is still in so unsatisfactory a state." Prof. 

 Newcomb gives an excellent account of the various 

 hypotheses as to the state of the upper regions of the 

 atmosphere. We have not found any allusion to the 

 wav in which observed refractions are mixed up with 

 division error, and R-D discordance. The question 

 of svstematic corrections has been reserved for a later 

 chapter. 



The ninth chapirr, the last of part ii., is devoted to 

 precession and nutation. This chapter, in particular, 

 is full of formula; .and data for practical use, and, 

 like the previous chapter, it concludes with an excel- 

 lent bibliography. 



Part iii. is devoted to the " reduction and deter- 

 mination of positions of the fixed stars." It is the 

 part of the book where the author at length closes 

 with the observations, and to which the previous parts 

 are in fact merely introductory. But even now two 

 more chapters of an introductory kind still remain, 

 chapter x., on the application of precession and proper 

 motion, chapter xi., on star corrections. In chapter 

 xii. we come to a description of the methods of obser- 

 vation and allusion to the systematic errors to which 

 observation is liable. 



Chapter xiii. may be regarded as the real purpose 

 of the book. It describes how individual catalogues 

 are corrected so as to reduce them to an adopted 

 system, and thus render them comparable with one 

 another. .\t the end of the chapter is given a list 

 of star catalogues. 



The book concludes with an appendix giving tables 

 and precepts for their use. W'e are inclined to con- 

 sider some of these tables a mistake, or, at least, 

 their inclusion in this book a mistake. The fact is 

 that tables in constant use wear out very fast, and we 



