all so closely together that they
cannot be critically examined; but when more than one prism is used
and the spectrum by this means spread out widely, the dark lines are
made to stand apart. They are then found to number many thousands. We
speak now of the analysis of sunlight. Experimentation was naturally
turned, however, to terrestrial gases and solids on fire, and it was
found that these also produce like series of dark lines in the
spectrum. Or when the substances are consumed _as solids_, then the
spectral effects are reversed, and the lines that would be dark lines
in the luminous colored spectrum become themselves luminous lines on
the screen; but these lines hold the same relation in mathematical
measurement, etc., as do the _dark_ lines in the colored spectrum.

Skillful spectroscopists succeeded in detecting and delineating the
lines that were peculiar to each substance. By burning such substances
in flame, they were able to produce the lines, and thus verify
results. By such experimentation the various lines present in the
solar spectrum were separated from the complex result, and the
conclusion was reached that in the burning surface of the sun certain
substances _well known on earth are present_; for the lines of those
substances are shown in the spectrum.

No other known substances would produce the given lines. The
conclusion is overwhelming that the substances in question are present
in a gaseous condition in the burning flames of the sun. Down to the
present time the examination of the sun's atmosphere has shown the
existence therein of thirty-six known elements. These include sodium,
potassium, calcium, magnesium, iron, copper, cobalt, silver, lead,
tin, zinc, titanium, aluminium, chromium, silicon, carbon, hydrogen
and several others.

It was thus established that in the constitution of the sun many of
the well-known elements of the earth are present. There could be no
mistake about it. An identity of lines in such a case proved beyond
dispute the identity of the substance from which such lines are
derived. The existence of common materials in the central sphere of
our system and in _one_ of his attendant orbs--our own--could not be
doubted. The discovery of such a fact led by immediate inference to
the expectation and belief that the _other_ planets were of like
constitution, or in a word, that the whole solar system was
essentially composed of identical materials.

As the inquiry proceeded, i