be sufficiently intense, the bands belonging to the metal
reveal themselves with perfect definition. Into holes drilled in a
cylinder of retort carbon, pure culinary salt is introduced. When the
carbon is made the positive electrode of the lamp, the resultant
spectrum shows the brilliant yellow lines of the metal sodium.
Similar experiments made with the chlorides of strontium, calcium,
lithium, [Footnote: The vividness of the colours of the lithium
spectrum is extraordinary; the spectrum, moreover, contained a blue
band of indescribable splendour. It was thought by many, during the
discourse, that I had mistaken strontium for lithium, as this blue
band had never before been seen. I have obtained it many times since;
and my friend Dr. Miller, having kindly analysed the substance made
use of, pronounces it pure chloride of lithium.--J. T.] and other
metals, give the bands due to the respective metals. When different
salts are mixed together, and rammed into holes in the carbon; a
spectrum is obtained which contains the bands of them all.

The position of these bright bands never varies, and each metal has
its own system. Hence the competent observer can infer from the bands
of the spectrum the metals which produce it. It is a language
addressed to the eye instead of the ear; and the certainty would not
be augmented if each metal possessed the power of audibly calling out,
'I am here!' Nor is this language affected by distance. If we find
that the sun or the stars give us the bands of our terrestrial metals,
it is a declaration on the part of these orbs that such metals enter
into their composition. Does the sun give us any such intimation?
Does the solar spectrum exhibit bright lines which we might compare
with those produced by our terrestrial metals, and prove either their
identity or difference? No. The solar spectrum, when closely
examined, gives us a multitude of fine dark lines instead of bright
ones. They were first noticed by Dr. Wollaston, but were multiplied
and investigated with profound skill by Fraunhofer, and named after
him Fraunhofer's lines. They had been long a standing puzzle to
philosophers. The bright lines yielded by metallic vapours had been
also known to us for years; but the connection between both classes of
phenomena was wholly unknown, until Kirchhoff, with admirable
acuteness, revealed the secret, and placed it at the same time in our
power to chemically analyse the sun.

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