6o THE POPULAR SCIENCE MONTHLY. 



with existing instruments, to obtain results of extreme value from ob- 

 servations kept up with persistence and scrupulous care for several 

 years at the top of some rainless mountain, if such can be found ; but 

 the undertaking would be a difficult and serious affair, quite beyond 

 any private means. 



Related to this subject is the problem of the connection between 

 the activity of the solar surface and magnetic disturbances on the 

 earth — a connection unquestionable as matter of fact, but at present 

 unexplained as matter of theory. It may have something to do with 

 the remarkable prominence of iron in the list of solar materials ; or 

 the explanation may, perhaps, be found in the mechanism by means of 

 which the radiations of light and heat traverse interplanetary space, 

 presenting itself ultimately as a corollary of the perfected electro- 

 magnetic theory of light. 



The chromosphere and prominences present several problems of 

 interest. One of the most fruitful of them relates to the spectroscopic 

 phenomena at the base of the chromosphere, and especially to the 

 strange differences in the behavior of different spectrum-lines, which, 

 according to terrestrial observations, are due to the same material. 

 Of two lines (of iron, for instance) side by side in the spectrum, 

 one will glow and blaze, while the other will sulk in imperturbable 

 darkness ; one will be distorted and shattered, presumably by the 

 swift motion of the iron vapor to which it is due, while the other 

 stands stiff and straight. Evidently there is some deep-lying cause 

 for such differences ; and as yet no satisfactory explanation appears 

 to me to have been reached, though much ingenious speculation has 

 been expended uj)on it. Mr. Lockyer's bold and fertile hypothesis, 

 already alluded to, that at solar and stellar temperatures our elements 

 are decomposed into others more elemental yet, seems to have failed 

 of demonstration thus far, and rather to have lost ground of late ; and 

 yet one is almost tempted to say, " It ought to be true," and to add 

 that there is more than a possibility that its essential truth will be 

 established some time in the future. 



Probably all that can be safely said at present is, that the spectrum 

 of a metallic vapor (iron, for instance, as before) depends not only 

 upon the chemical element concerned, but also upon its physical con- 

 ditions ; so that, at different levels in the solar atmosphere, the spec- 

 trum of the iron will differ greatly as regards the relative conspicu- 

 ousness of different lines ; and so it will happen that, whenever any 

 mass of iron vapor is suffering disturbance, those lines only which par- 

 ticularly characterize the spectrum of iron in that special state will be 

 distorted or reversed, while all their sisters will remain serene. 



The problem of the solar corona is at present receiving much at- 

 tention. The most recent investigations respecting it — those of Dr. 

 Huggins and Professor Hastings — tend in directions which appear to 

 be diametrically opposite. Dr. Huggins considers that he has sue- 



