alt 19
Hydrogen 4
Aluminium 2
Zinc 2
Copper 7

The probability is overwhelming that all these substances exist in the
atmosphere of the sun.

Kirchhoff's discovery profoundly modified the conceptions previously
entertained regarding the constitution of the sun, leading him to
views which, though they may be modified in detail, will, I believe,
remain substantially valid to the end of time. The sun, according to
Kirchhoff, consists of a molten nucleus which is surrounded by a
flaming atmosphere of lower temperature. The nucleus may, in part, be
_clouds_, mixed with, or underlying true vapour. The light of the
nucleus would give us a continuous spectrum, like that of the Drummond
light; but having to pass through the photosphere, as Kirchhoff's beam
passed through the sodium flame, those rays of the nucleus which the
photosphere emit are absorbed, and shaded lines, corresponding to the
rays absorbed, occur in the spectrum. Abolish the solar nucleus, and
we should have a spectrum showing a bright line in the place of every
dark line of Fraunhofer, just as, in the case of Kirchhoff's second
experiment, we should have the bright sodium lines of the flame if the
lime-light were withdrawn. These lines of Fraunhofer are therefore not
absolutely dark, but dark by an amount corresponding to the difference
between the light intercepted and the light emitted by the
photosphere.

Almost every great scientific discovery is approached
contemporaneously by many minds, the fact that one mind usually
confers upon it the distinctness of demonstration being an
illustration, not of genius isolated, but of genius in advance. Thus
Foucault, in 1849, came to the verge of Kirchhoff's discovery. By
converging an image of the sun upon a voltaic arc, and thus obtaining
the spectra of both sun and arc superposed, he found that the two
bright lines which, owing to the presence of a little sodium in the
carbons or in the air, are seen in the spectrum of the arc, coincide
with the dark lines D of the solar spectrum. The lines D he found to
he considerably strengthened by the passage of the solar light through
the voltaic arc.

Instead of the image of the sun, Foucault then projected upon the arc
the image of one of the solid incandescent carbon points, which of
itself would give a continuous spectrum; and he found that the lines D
were thus _generated_ in that spectrum. Foucault's conclusion from
this admirable exper