February 2, 1899] 



NA TURE 



315 



YOUNG'S GENERAL ASTRONOMY. 

 A Text-book 0/ General Astronomy- By Charles A. 

 Young. Revised edition. Pp. ix + 630. (London : 

 Ginn and Co., 189S.) 



E\'ERY student of astronomy is familiar with this 

 well-known text-book, and it is not too much to 

 say that it is as well used this side of the Atlantic as it 

 is on the other. Written for a general course in colleges 

 and schools, and meant to supply that amount of inform- 

 ation upon the subject which may fairly be expected of 

 "every liberally educated person," it is only natural that 

 too great an attention to details must give way to more 

 general statements. Since the first publication of this 

 volume, now nearly ten years ago, astronomical science 

 has made rapid changes and advances, and the time 

 necessarily comes when minor alterations, notes, and 

 addenda, .ic., in subsequent editions of a text-book like 

 this cannot be satisfactorily inserted without considerable 

 difficulty, and probably detriment to the book itself 

 Prof. Young has therefore thoroughly revised his text- 

 book, and it is this new edition that we have now before 

 us. A glance through the pages of this book, with an 

 occasional reference to the older volume, displays many 

 differences and additions of new matter. In Chapter ix., 

 for instance, we notice that the illustration of the tele- 

 spectroscope has been replaced by a nearly full-page 

 plate of the large grating spectroscope of the Halstead 

 Observatory. In another paragraph, describing a sun- 

 spot spectrum, an excellent reproduction of a photograph 

 of the yellow-green portion of a spot spectrum is added, 

 giving the reader a good idea of the meaning of widened 

 lines in sun-spot spectra. Prof Young refers in another 

 paragraph to the so-called " reversing layer," describing 

 the phenomenon as he saw it in the Spanish eclipse of 

 1870. The only additional matter here added is a brief 

 note, in which it is stated that the photograph of the 

 chromosphere taken in Novaya Zemlya in 1896 "fully 

 confirms the author's visual observations, and appears to 

 establish the reality of the 'reversing layer.'" We may 

 mention that photographs taken at Viziadrug in 1898 

 were more numerous and on a far larger scale than any 

 obtained previously, and have yielded very important 

 results on this very question. Photographs of the so- 

 called " reversing layer" were obtained on several plates 

 successively exposed during twelve seconds, and a com- 

 parison of the chromosphere with the solar spectrum 

 shows many important differences. In fact, to use 

 Sir Norman Lockyer's own words (Nature, No. 1515, 

 vol. lix.) — 



"... practically the lower part of the sun's atmosphere, 

 if present by itself, would give us the lines which 

 specialise the spectra of y Cygni or Procyon. I recog- 

 nise in this result a veritable Rosetta stone which will 

 enable us to read the celestial hieroglyphics presented to 

 us in stellar spectra, and help us to study the spectra 

 and to get at results much more distinctly and certainly 

 than ever before." 



In that part of the same chapter in which the photo- 

 graphy of prominences and chromosphere is discussed. 

 Prof Young mentions that both Hale and Deslandres 

 have devised ingenious arrangements (called spectro- 

 heliographs) by which they are able "to obtain pictures 

 NO. 1527, VOL. 59] 



of the chromosphere and prominences around the whole 

 circumference of the sun at once." Although the text 

 has been carefully perused, the author does not seem to 

 have made it sufficiently clear that besides the pheno- 

 mena around the circumference, those on the solar disc 

 can be photographed by the same means. 



In the chapter devoted to the planets and their 

 motions we find that a thorough revision has taken 

 place, and more especially in respect to the recent 

 values of their elements. Prof. Keeler's beautiful con- 

 firmation of the meteoric theory of the satellites of 

 .Saturn by means of the spectroscope is clearly described 

 and illustrated. 



Lastly, it is interesting to note that in Prof. Young's 

 opinion the meteoritic hypothesis is gaining ground, for 

 to use his own words — 



" While it would be premature to endorse this specu- 

 lation of Mr. Lockyer's as an established discovery (since 

 there remain in it many obscure and doubtful points), 

 there can be little doubt that it marks an epoch in the 

 history of opinion." 



Before bringing this notice to a conclusion it may be 

 stated that the present volume will continue to hold its 

 high position among text-books on this side of the 

 Atlantic. The same standard of clearness of exposition 

 has been maintained throughout, and the illustrations 

 are all to the point. Misprints are very few and far 

 between, and only one has been discovered in our 

 examination, namely, that on p. 536, line 1 1 from top, 

 where "filled" is printed for "fitted." 



W. J. S. L. 



OUR BOOK SHELF. 

 The Campaign in t/ie Tij-ali. Bj- Colonel H. D. 



Hutchinson. Pp. xvi -t- 250. (London : Macmillan 



and Co., Ltd., 1S98.) 

 The "Campaign in the Tirah" is for the most part a 

 reprint of the letters which appeared in the Times during 

 the progress of that expedition, which were written 

 by the author of the present book, and which must be 

 fresh in the minds of the reading public. But Colonel 

 Hutchinson has added to them an introduction in which 

 he deals with the probable causes of the general outbreak 

 on the north-west of India, and an appendix in which he 

 sums up the lessons to be learnt from the campaign, and 

 points the military moral of the whole story. Both these 

 additions are valuable. From the point of vantage of 

 his official position as Director General of military educa- 

 tion in India, Colonel Hutchinson has been able to watch 

 the development of those issues of our frontier policy 

 which have been discussed so freely in England, with 

 more discrimination, and with a more unbiassed mind, 

 than falls to the lot of many public officials who are 

 committed to the support of Government policy. And 

 he is, at the same time, best qualified to gather instructive 

 morals from the object-lessons of the campaign. 



In the introduction we have a very clear expression 

 of opinion as to the meaning of the outbreak, and the 

 origin of it ; and we shall probably not be far wrong if we 

 assume that this opinion tallies closely with that of every 

 frontier official who is in direct touch with Pathan com- 

 munities, or who is conversant with the views of educated 

 Mahomedan gentlemen in the Punjab. Colonel Hutchinson 

 traces the universal uprising of the Pathan tribes along 

 the whole line of the frontier to the natural fear of losing 

 their independence, which was roused by the process of 



