396 THE POPULAR SCIENCE MONTHLY. 



This was done by fanning out with a powerfully dispersive spec- 

 troscope the diffused radiance near the sun, until it became suffi- 

 ciently attenuated to permit the delicate flame-lines to appear upon 

 its rainbow-tinted background. This mischievous radiance — which 

 it is the chief merit of a solar eclipse to abolish during some brief 

 moments — is due to the action of the atmosphere, and chiefly of the 

 watery vapors contained in it. Were our earth stripped of its 

 " cloud of all-sustaining air," and presented, like its satellite, bare to 

 space, the sky would appear perfectly black up to the very rim of the 

 sun's disk — a state of things of all others (vital necessities apart) the 

 most desirable to spectroscopists. The best approach to its attain- 

 ment is made by mounting a few thousand feet above the earth's sur- 

 face. In the drier and purer air of the mountains, " glare " notably 

 diminishes, and the tell-tale prominence-lines are thus more easily dis- 

 engaged from the effacing luster in which they hang, as it were, sus- 

 pended. 



The Peak of Teneriffe, as we have seen, offers a marked exception 

 to this rule, the impalpable dust diffused through the air giving, even 

 at its summit, precisely the same kind of detailed reflection as aqueous 

 vapors at lower levels. It is accordingly destitute of one of the chief 

 qualifications for serving as a point of vantage to observers of the 

 new type. 



The changes in the spectra of chromosphere and prominences (for 

 they are parts of a single appendage) present a subject of unsurpassed 

 interest to the student of solar physics. There, if anywhere, will be 

 found the key to the secret of the sun's internal economy ; in them, if 

 at all, the real condition of matter in the unimaginable abysses of heat 

 covered up by the relatively cool photosphere, whose radiations could, 

 nevertheless, vivify 2,300,000,000 globes like ours, will reveal itself ; 

 revealing, at the same time, something more than we now know of the 

 nature of the so-called " elementary " substances, hitherto tortured, 

 with little result, in terrestrial laboratories. 



The chromosphere and prominences might be figuratively described 

 as an ocean and clouds of tranquil incandescence, agitated and inter- 

 mingled with water-spouts, tornadoes, and geysers of raging fire. Cer- 

 tain kinds of light are at all times emitted by them, showing that 

 certain kinds of matter (as, for instance, hydrogen and "helium"*) 

 form invariable constituents of their substance. Of these unfailing 

 lines Professor Young counts eleven.f But a vastly greater number 

 appear only occasionally, and, it would seem capriciously, under the 

 stress of eruptive action from the interior. And precisely this it is 

 which lends them such significance ; for of what is going on there 



* The characteristic orange line (Ds) of this unknown substance has recently been 

 identified by Professor Palmieri in the spectrum of lava from Vesuvius — a highly inter- 

 esting discovery, if verified. 



f "The Sun," p. 193. 



