rity in the
incandescent lime, is exhausted. Kirchhoff formed a spectrum of the
limelight, and after the two bright lines had vanished, he placed his
salt flame in front of the slit. The two dark lines immediately
started forth. Thus, in the continuous spectrum of the lime-light, he
evoked, artificially, the lines D of Fraunhofer.

Kirchhoff knew that this was an action not peculiar to the sodium
flame, and he immediately extended his generalisation to all coloured
flames which yield sharply defined bright bands in their spectra.
White light, with all its constituents complete, sent through such
flames, would, he inferred, have those precise constituents absorbed,
whose refrangibilities are the same as those of the bright bands; so
that after passing through such flames, the white light, if
sufficiently intense, would have its spectrum furrowed by bands of
darkness. On the occasion here referred to Kirchhoff also succeeded in
reversing a bright band of lithium.

The long-standing difficulty of Fraunhofer's lines fell to pieces in
the presence of facts and reflections like these, which also carried
with them an immeasurable extension of the chemist's power. Kirchhoff
saw that from the agreement of the lines in the spectra of terrestrial
substances with Fraunhofer's lines, the presence of these substances
in the sun and fixed stars might be immediately inferred. Thus the
dark lines D in the solar spectrum proved the existence of sodium in
the solar atmosphere; while the bright lines discovered by Brewster in
a nitre flame, which had been proved to coincide exactly with certain
dark lines between A and B in the solar spectrum, proved the existence
of potassium in the sun.

All subsequent research verified the accuracy of these first daring
conclusions. In his second paper, communicated to the Berlin Academy
before the close of 1859, Kirchhoff proved the existence of iron in
the sun. The bright lines of the spectrum of iron vapour are
exceedingly numerous, and 65 of them were subsequently proved by
Kirchhoff to be absolutely identical in position with 65 dark
Fraunhofer's lines. Angstroem and Thalen pushed the coincidences to 450
for iron, while, according to the same excellent investigators, the
following numbers express the coincidences, in the case of the
respective metals to which they are attached:--

Calcium 75
Barium 11
Magnesium 4
Manganese 57
Titanium 118
Chromium 18
Nickel 33
Cob