THE POPULAR SCIENCE MONTHLY. 



an observer of solar phenomena, the chap- 

 ters on the sun are among the most inter- 

 esting, instructive, and generally valuable 

 portions of the book. It is worth while to 

 quote two or three passages from these chap- 

 ters in which he sums up the latest results 

 of investigation and theory. After quoting 

 Secchi's later eruption theory of sun-spots, 

 and pointing out an obvious objection to it, 

 he remarks : " Perhaps the true explanation 

 may be that when an eruption occurs at any 

 spot the photosphere somewhere in the neigh- 

 borhood settles down in consequence of the 

 diminution of the pressure beneath, thus form- 

 ing a ' sink,^ so to speak, which is of course 

 covered by a greater depth of cooler vapors 

 above, and so looks dark " (p. 190). 



In regard to the disputed question of the 

 influence of solar disturbances, as indicated 

 by sun-spots, upon the meteorology of the 

 earth, concerning which some extravagant 

 notions have recently been set forth. Prof. 

 Young says, " It is now quite certain that 

 whatever influence the sun-spots exert upon 

 terrestrial meteorology is very slight, if it 

 exists at all." This statement, coming from 

 one who ranks so high as an authority on 

 solar physics, must be rather discouraging 

 to those who have been trying to fix the re- 

 sponsibility for every great tornado, or other 

 unusually destructive storm of late years, 

 upon some unfortunate sun-spot. 



Our author speaks with characteristic 

 modesty, and yet very interestingly, of the 

 phenomenon of " the reversing layer," first 

 observed by him during the solar eclipse of 

 18*70, and which seems to indicate the exist- 

 ence of a gaseous stratum or shell surround- 

 ing the photosphere, and not above five hun- 

 dred miles in thickness, to which the forma- 

 tion of the dark lines in the solar spectrum 

 is mainly due. While by no means aban- 

 doning his own opinion of the probable na- 

 ture of this phenomenon, he frankly states 

 the opposing view of Mr. Lockyer, and points 

 out how observation may be directed to set- 

 tle the question. 



A most inspiring and encouraging state- 

 ment for those who may be troubled by 

 doubts as to whether any important discov- 

 eries remain to be achieved by future stu- 

 dents of the sun is that "among the many 

 thousand lines of the solar spectrum only a 

 few hundred are so far identified." There 



are twelve elements familiar to us on the 

 earth, which are known to exist in the sun, 

 and nine others of whose existence there 

 the evidence is not quite conclusive. Prof. 

 Young does not pronounce quite so positively 

 as some foreign savants have done against 

 the validity of Dr. Henry Draper's conclu- 

 sion that his photographs had demonstrated 

 the presence of oxygen in the sun, but he re- 

 marks that the latest work appears to turn 

 the balance of evidence the other way. He 

 still accepts Rosetti's determination of the 

 effective temperature of the sun, 18,000° 

 Fahr., as being the most probable that has 

 yet been obtained. 



The extraordinary mental picture that 

 we must form of the solar globe, as a body 

 in the gaseous condition and yet possessing 

 in its nuclear mass a consistency like that of 

 tar, has become familiar to readers of the 

 literature of science since the publication 

 of Prof. Young's admirable book on " The 

 Sun," In the present work he presents in 

 briefer form the same general conclusions 

 concerning the constitution of the sun. There 

 are few who will be disposed to accept by 

 preference the views of those who hold that 

 the great mass of the sun is probably liquid 

 instead of gaseous. The brief synopses given 

 of our knowledge of the nature of the visible 

 phenomena of the sun are exceedingly clear 

 and succinct. To begin with the photosphere, 

 which, as the reader knows, is the visible 

 surface of the sun, from which the splendor 

 of its light arises : " The photosphere is prob- 

 ably a shell of incandescent clouds, formed by 

 the condensation of the vapors which are 

 exposed to the cold of space. 



" The photospheric clouds float in an at- 

 mosphere containing, still uncondensed, a 

 considerable quantity of the same vapors out 

 of which they themselves have been formed, ]ust 

 as in our own atmosphere the air around a 

 cloud is still saturated with water vapor. . . . 



" The chromosphere and prominences are 

 composed of the permanent gases, mainly hy- 

 drogen and helium. , . . The appearances 

 are for the most part as if the chromosphere 

 was formed of jets of heated hydrogen as- 

 cending through the interspaces between the 

 photospheric clouds, like flames playing over 

 a coal-fire. 



" The corona also rests on the photo- 

 sphere, . . . but extends to a far greater ele- 



