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The simultaneous picturing, moreover, of the entire chromospheric ring, with whatever trees or fountains of fire chance to be at the moment issuing from it, has been accomplished by a very simple device.
Happily, however, the unanswerable arguments of the photographic camera were soon to be made available against such hardy incredulity. Thus, the virtual discovery of the solar appendages, both coronal and chromospheric, may be said to have been begun in 1842, and completed in 1851. The current Herschelian theory of the solar constitution remained, however, for the time, intact.
In March, 1895, Professor Ramsay obtained from the rare mineral clevite a volatile gas, the spectrum of which was found to include the yellow prominence-ray. Helium was actually at hand, and available for examination. The identification cleared up many obscurities in chromospheric chemistry.
This inference was fully borne out by the researches of Wüllner; and Janssen expressed the opinion that the chromospheric gases are rarefied almost to the degree of an air-pump vacuum. Hence was derived a general and fully justified conviction that there could be outside, and incumbent upon the chromosphere, no such vast atmosphere as the corona appeared to represent.
The reflected light derived from the corona was weaker than in 1878, while its original emissions were proportionately intensified. Nevertheless, most of the bright lines recorded as coronal were really due, there can be no doubt, to diffused chromospheric light.
An instructive example is that of the chromospheric element helium. Father Secchi remarked in 1868 that there is no dark line in the solar spectrum matching its light; and his observation has been fully confirmed. Helium-absorption is, however, occasionally noticed in the penumbræ of spots. Our terrestrial vital element might then easily subsist unrecognisably in the sun.
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.
It served to bring out at least one important fact that of the uncommon strength in chromospheric regions of the twin violet beams of calcium, designated "H" and "K"; and prominence-photography signalised its improvement by the registration, in the spectrum of one such object, of twenty-nine rays, including many of the ultra-violet hydrogen series discovered by Sir William Huggins in the emission of white stars.
Maunder conjectures all "white" nebulæ to be made up of sunlets in which the coronal element predominates, while chromospheric materials assert their presence in nebulæ of the "green" variety. Among the ascertained analogies between the stellar and nebular systems is that of variability of light. On October 11, 1852, Mr. Hind discovered a small nebula in Taurus.
It is difficult to imagine by what chromospheric machinery this curious result can be produced. Alcyone in the Pleiades presents the same characteristic. Alone among the hydrogen lines, crimson C glows in its spectrum, while all the others are dark. Luminosity of the Wolf-Rayet kind is particularly constant, both in quantity and quality.
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