great dispersive power that the continuous spectrum reflected by our
atmosphere should be greatly weakened, while a bright line would
suffer no diminution by the high dispersion. On October 20th
Lockyer,[10] having news of the eclipse, but not of Jansen's
observations the day after, was able to see these lines. This was a
splendid performance, for it enabled the prominences to be observed,
not only during eclipses, but every day. Moreover, the next year
Huggins was able, by using a wide slit, to see the whole of a
prominence and note its shape. Prominences are classified, according
to their form, into "flame" and "cloud" prominences, the spectrum of
the latter showing calcium, hydrogen, and helium; that of the former
including a number of metals.

The D line of sodium is a double line, and in the same eclipse (1868)
an orange line was noticed which was afterwards found to lie close to
the two components of the D line. It did not correspond with any known
terrestrial element, and the unknown element was called "helium." It
was not until 1895 that Sir William Ramsay found this element as a gas
in the mineral cleavite.

The spectrum of the corona is partly continuous, indicating light
reflected from the sun's body. But it also shows a green line
corresponding with no known terrestrial element, and the name
"coronium" has been given to the substance causing it.

A vast number of facts have been added to our knowledge about the sun
by photography and the spectroscope. Speculations and hypotheses in
plenty have been offered, but it may be long before we have a complete
theory evolved to explain all the phenomena of the storm-swept
metallic atmosphere of the sun.