SCIENTIFIC LITERATURE. 563 



ever came more opportunely than this new edition of The Sun. Within the 

 past few jears discovery has followed discovery, and theory has obscured 

 theory in solar physics so rapidly that the general reader, desirous to keep 

 on safe ground, has found himself in a more or less uncomfortable position. 

 One authority, of great weight, has been telling him that the " faculse" and 

 the "prominences" are identical phenomena; another authority, of per- 

 haps equal weight, has assured him that this is not so. Likewise, in regard 

 to the most interesting question of the connection of sun spots with terres- 

 trial magnetism: on the one hand stand positive as.sertions of an intimate 

 relationship of that kind, and on the other hand stands Lord Kelvin 

 with his dictum and the dicta of Kelvin in science have frequently been 

 deemed of equal weight to those of Lord Coke in law asserting that " we 

 may be forced to conclude that the supposed connection between magnetic 

 storms and sun spots is unreal, and that the seeming agreement between 

 the periods has been a mere coincidence." 



Then there have been new theories of sun-spots, new determinations of 

 the solar parallax, new identifications of elements in the sun, the wonderful 

 work of Langley on the infra-red portion of the spectrum, the questions 

 raised by Lockyer's theory of the "dissociation" of elements in the sun, 

 the question of the existence of oxygen in the solar atmosphere, the ques- 

 tion whether the sun-spots are really depressions, and many other new and 

 puzzling things, the most surprising of all being, perhaj^s, the discovery in 

 a Norwegian mineral of " helium," an element which had been found in 

 the sun as long ago as 1868, but the presence of which on the earth had 

 never been detected. 



Amid such a confusion the unprofessional wayfarer in science needs a 

 guiding hand, and that is what Prof. Young now most seasonably offers. 

 There is a fairness, a power of discrimination, and a judicial balance in our 

 author's treatment of vexed questions that must create in the reader's mind 

 both confidence and admiration. His brief, shrewd reply to the remark of 

 Lord Kelvin, quoted above, concerning sun-spots and magnetic storms, will 

 find many highly interested readers, and it is made all the more attractive 

 by the vista of possible future discovery which it opens with the suggestion 

 that "it is not perhaps outside the limits of possibility that both the solar 

 and terrestrial disturbance have a common origin in some invasion of 

 power or matter from outer space that the solar tumult is the brother, and 

 not the father, of our own aurora." 



Prof. Young's discussion of Helium, its Identification and Properties, 

 is, of course, luminous and informing in the highest degree. Nothing can 

 be more pleasing than to note the manner in which an unexpected dis- 

 covery, full of momentous consequences for the work with which he is 

 identified, is received, assimilated, and irradiated by the mind of a leader 

 in science. 



Among the new matters treated, one of the most interesting, because it 

 relates to hoped-for advances in the future, is the effort to render the 

 corona visible when the sun is not eclipsed. It is certainly encouraging to 

 know that to Prof. Young " the case appears by no means absolutely hope- 

 less." When we remember the advance in our knowledge of the promi- 

 nences following Janssen's and Lockyer's discovery in 1868, that those 

 phenomena could be rendered visible with the spectroscope in ordinary 

 daylight, and consider the ignorance that probably would have i^revailed 



