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The new lines, accordingly, filled places in a manner already prepared for them, and were thus unmistakably associated with the hydrogen-spectrum. This is now known to be represented in prominences by twenty-seven lines, forming a kind of harmonic progression, only four of which are visibly darkened in the Fraunhofer spectrum of the sun. The chemistry of "cloud-prominences" is simple.
They made apparent a close connection between coronal outflows and chromospheric jets, cone-shaped beams serving as the sheaths, or envelopes, of prominences. M. Hansky, indeed, thought that every streamer had a chromospheric eruption at its base.
Astronomers, thus liberated, by the acquisition of power to survey them at any time, from the necessity of studying prominences during eclipses, were able to concentrate the whole of their attention on the corona. The first thing to be done was to ascertain the character of its spectrum.
Her shaggy, loose-jointed body, her irregular, sketchy outlines, like those of the landscape the hollows and ridges, the slopes and prominences her tossing horns, her bushy tail, her swinging gait, her tranquil, ruminating habits all tend to make her an object upon which the artist eye loves to dwell. The artists are for ever putting her into pictures too.
"There was certainly not the beauty of the eclipse of 1869. Then immense radiations shot out in all directions, and threw themselves over half the sky. In 1869, the rosy prominences were so many, so brilliant, so fantastic, so weirdly changing, that the eye must follow them; now, scarcely a protuberance of color, only a roseate light around the sun as the totality ended.
Here was a berg that had suddenly turned turtle and exposed its greater, under-water bulk to the air. About it the sea was dark and vivid blue, and the berg sparkled in the sun with prismatic reflections that gave all the hues of the rainbow to its prominences, while the bulk glowed like a fire opal. Between it and the schooner the sea ran in a lasher of diminishing turmoil.
I fancied it must be spirals of vapour that had caught the light and made this crest of fiery tongues against the sky, but indeed it was the solar prominences I saw, a crown of fire about the sun that is forever hidden from earthly eyes by our atmospheric veil. And then the sun!
The isolation of H and K in solar prominences from any other of the lines usually distinctive of calcium was experimentally proved by Sir William and Lady Huggins in 1897 to be due to the extreme tenuity of the emitting vapour.
Janssen's spectroscope furnished him besides with the strongest confirmation of what had already been reported by the telescope and the camera as to the continuous nature of the scarlet "sierra" lying at the base of the prominences. Everywhere at the sun's edge the same bright lines appeared. It was not until the 19th of September that Janssen thought fit to send news of his discovery to Europe.
At the eclipse of 1868, which the astronomers, aroused by the wonderful scene of 1842, and eager to test the powers of the newly invented spectroscope, flocked to India to witness, Janssen conceived the idea of employing the spectroscope to render the prominences visible when there was no eclipse. He succeeded the very next day, and these phenomena have been studied in that way ever since.
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