hat is the Sun made of? Comte mentioned as a problem, which it was
impossible that man could ever solve, any attempt to determine the
chemical composition of the heavenly bodies. "Nous concevons," he said,
"la possibilite de determiner leurs formes, leurs distances, leurs
grandeurs, et leurs mouvements, tandis que nous ne saurions jamais
etudier par aucun moyen leur composition chimique ou leur structure
mineralogique." To do so might well have seemed hopeless, and yet the
possibility has been proved, and a beginning has been made. In the early
part of this century Wollaston observed that the bright band of colours
thrown by a prism, and known as the spectrum, was traversed by dark
lines, which were also discovered, and described more in detail, by
Fraunhofer, after whom they are generally called "Fraunhofer's lines."
The next step was made by Wheatstone, who showed that the spectrum
formed by incandescent vapours was formed of bright lines, which
differed for each substance, and might, therefore, be used as a
convenient mode of analysis. In fact, by this process several new
substances have actually been discovered. These bright lines were found
on comparison to coincide with the dark lines in the spectrum, and to
Kirchhoff and Bunsen is due the credit of applying this method of
research to astronomical science. They arranged their apparatus so that
one-half was lighted by the Sun, the other by the incandescent gas they
were examining. When the vapour of sodium was treated in this way they
found that the bright line in the flame of soda exactly coincided with a
line in the Sun's spectrum. The conclusion was obvious; there is sodium
in the Sun. It must, indeed, have been a glorious moment when the
thought flashed upon them; and the discovery, with its results, is one
of the greatest triumphs of human genius.

The Sun has thus been proved to contain hydrogen, sodium, barium,
magnesium, calcium, aluminium, chromium, iron, nickle, manganese,
titanium, cobalt, lead, zinc, copper, cadmium, strontium, cerium,
uranium, potassium, etc., in all 36 of our terrestrial elements, while
as regards some others the evidence is not conclusive. We cannot as yet
say that any of our elements are absent, nor though there are various
lines which cannot as yet be certainly referred to any known substance,
have we clear proof that the Sun contains any element which does not
exist on our earth. On the whole, then, the chemical composition of the