Page:Popular Science Monthly Volume 26.djvu/410

396 This was done by fanning out with a powerfully dispersive spectroscope the diffused radiance near the sun, until it became sufficiently 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 attainment is made by mounting a few thousand feet above the earth's surface. In the drier and purer air of the mountains, "glare" notably diminishes, and the tell-tale prominence-lines are thus more easily disengaged from the effacing luster in which they hang, as it were, suspended.

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 intermingled with water-spouts, tornadoes, and geysers of raging fire. Certain 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. 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