February 22, 1894 



NA TURE 



;83 



of devoting a whole chapter to the members of the solar 

 system, or a large part of a chapter and a full-page plate 

 to eclipses of the moon ; again, the discussion of the 

 Glacial Period surely belongs more to the story of our 

 own planet than to that of the sun, and might very well 

 have been omitted. 



This method of treatment is the more objectionable 

 as it has evidently involved the omission of reference to 

 many observations of great interest, and must inevit- 

 ably tend to give the impression that our knowledge 

 is very much less than it is in reality. At the same time 

 it does an injustice alike to the reader, and to the army 

 of workers who devote their energies to the pursuit of 

 this branch of knowledge. 



Again, the story of thesun would certainly lose none of 

 its charm by historical treatment, but we look in vain for 

 even the barest mention of the names of Angstrom, 

 Thaltfn, Faye, Cornu, Perry, Balfour Stewart, and a host 

 of other workers who have taken so great a part in solar 

 inquiries. 



So far as it goes, however, the story of the sun is told 

 in that fascinating way which has deservedly brought the 

 author fame, and our greatest cause of complaint is that 

 it does not go far enough. The first five chapters, occu- 

 pying nearly one-third of the book, deal with the solar 

 system, the sun's distance, and the sun's mass. In these 

 well-worn subjects there is nothing new to tell and little 

 scope for novelty, but occasionally we come across some 

 of the bright illustrations at which the author is so 

 expert ; as, for instance, the endeavour to impress the 

 reader with the magnitude of the velocity of light. 



In chapter vi. a fair account is given of the total amount 

 and spectroscopic analysis of the "light of the sun." A 

 coloured plate of the solar spectrum is of unusual excel- 

 lence, but many of the finer details of Mr. Higgs's photo- 

 graphic spectrum are lost in the reproductions, and 

 scarcely do justice to the originals. 



After a chapter on the causes of eclipses, we come to 

 one on sun-spots, and here we first find evidence of the 

 incompleteness to which reference has been made. The 

 appearances presented by spots are fully described and 

 illustrated by a most liberal allowance of diagrams, but 

 no mention is made of "veiled spots." The rate of solar 

 rotation is discussed in considerable detail, but if the 

 spectroscopic results are to be mentioned at all, Duner's 

 observations might have found a place alongside those of 

 Mr. Crew. The author seems to favour the idea that the 

 varying rotation of the photosphere in different latitudes 

 is produced by the friction of concentric shells of the 

 matter of which it is formed ; other views, not less 

 probable, are utterly ignored ; as, for instance, one which 

 follows from the theory that spots are formed by down- 

 rushes of cool vapours — an explanation which Sir Robert 

 Ball has adopted as the most probable. The reader is 

 also left in blissful ignorance of the fact that astro- 

 nomers have taken the trouble to make a minute study 

 of the spectra of sun^pots, although this work has been 

 going on continuously for the last fifteen years, chiefly at 

 Kensington and Ston> hurst. Uf the existence of the 

 Committee on Solar Phvsics, and of the continuous 

 photographic record of the spots which it has organised, 

 the author seems to have no knowledge. Even the 

 importance of the eleven-yearly period does not appear 

 MO. 1269, VOL. 49] 



to be clearly grasped, and only the very briefest references 

 are made to this fundamental solar unit. 



The chapter on solar prominences contains most of 

 the ordinary information on the subject, and has the 

 merit of including some of the most recent observations 

 by Trouvelot and Fenyi. In addition, Prof. Hale's 

 remarkable work in photographing these objects is con- 

 sidered in some detail. Very little attempt is made, 

 however, to distinguish between quiet and eruptive 

 prominences. 



The solar corona is dismissed in very few words, and 

 the illustrations have not been well chosen. In giving a 

 somewhat detailed account of the American expedition to 

 French Guiana to observe the eclipse of December 1889? 

 it would have been gracious to record the fact that it was 

 during an expedition to this place at the same time that 

 the late Father Perry met with his fate. The authors 

 estimate of our spectroscopic knowledge of the corona is 

 very low, and it is disposed of in twenty lines ; but this 

 meagre description is due to the fact that the most recent 

 observations referred to are those made by Janssen 

 in 1871 ! 



It has been well remarked that ''hypothesis is the 

 soul of investigation,'' but our author makes no at- 

 tempt to give a full or complete account of any theory ; 

 apparently on the ground that we are still so " very 

 ignorant concerning the actual physical nature of the 

 great luminary." The principal pomt of theory touched 

 upon is that which concerns the materials of which 

 the photosphere is composed, the ordinary view that it 

 consists of glowing clouds being accepted. Working on 

 the lines of a suggestion made by Dr. Johnstone Sloney 

 in 1867, the author argues in favour of the view that 

 to carbon " belongs the distinction of being the main 

 source whence sunlight is dispensed." (p. 289.) This 

 certainly seems as probable as the generally accepted 

 idea that the photosphere consists of liquid metals, but 

 it does not give us any further insight into the causes of 

 the various phenomena which are observed. The study 

 of the circulation of the sun's atmosphere will no doubt 

 eventually furnish the key to most of the problems of 

 solar physics ; but here our author leaves us, with nothing 

 more than an unexplained diagram illustrating a theory 

 of the solar currents. 



Of the chapter dealing with solar and magnetic 

 phenomena, we have only to note that the author 

 lepeats the mistake with reference to the Carrington- 

 H.idgson outburst — a subject which has already been 

 discussed in these columns. He makes a suggestion, 

 however, which may be well worth consideration, namely, 

 that the solar and magnetic disturbances may not stand 

 in the relation of cause and effect at all, but are each of 

 them "manifestations of some other influence of electro- 

 magnetic waves on a vast scale sweeping through our 

 system, and mfluencing the magnetic phenomena in the 

 various bodies of which our system is composed." (p. 234). 



We see the author at his beat in the ne<t three chap, 

 ters, discussing step by step the probable cause of the 

 maintenance of solar radiation. The somewhat difficult 

 subject of molecular physics no longer remains obscure 

 under the influence of his luminous exposition, and their 

 application to the sun will be clear to any intelligent 

 reader. This part of the subject is only marred by the 



