nge in
1889.[680] It was by Professor Rowland shown to be irresistible. Two
hundred carbon-lines were, through his comparisons, sifted out from
sunlight, and it contains others significant of the presence of
silicon--a related substance, and one as important to rock-building on
the earth, as carbon is to the maintenance of life. The general result
of Rowland's labours was the establishment among solar materials, not
only of these two out of the fourteen metalloids, or non-metallic
substances, but of thirty-three metals, including silver and tin. Gold,
mercury, bismuth, antimony, and arsenic were discarded from the
catalogue; platinum and uranium, with six other metals, remained
doubtful; while iron was recorded as crowding the spectrum with over two
thousand obscure rays.[681] Gallium-absorption was detected in it by
Hartley and Ramage in 1889.[682]

Dr. Henry Draper[683] announced, in 1877, his imagined discovery, in the
solar spectrum, of eighteen especially brilliant spaces corresponding to
oxygen-emissions. But the agreement proved, when put to the test of very
high dispersion, to be wholly illusory.[684] Nor has it yet been found
possible to identify, in analysed sunlight, any significant _bright_
beams.[685]

The book of solar chemistry must be read in characters exclusively of
absorption. Nevertheless, the whole truth is unlikely to be written
there. That a substance displays none of its distinctive beams in the
spectrum of the sun or of a star, affords scarcely a presumption against
its presence. For it may be situated below the level where absorption
occurs, or under a pressure such as to efface lines by widening and
weakening them; it may be at a temperature so high that it gives out
more light than it takes up, and yet its incandescence may be masked by
the absorption of other bodies; finally, it may just balance absorption
by emission, with the result of complete spectral neutrality. An
instructive example is that of the chromospheric element helium. Father
Secchi remarked in 1868[686] that there is no dark line in the solar
spectrum matching its light; and his observation has been fully
confirmed.[687] Helium-absorption is, however, occasionally noticed in
the penumbrae of spots.[688]

Our terrestrial vital element might then easily subsist unrecognisably
in the sun. The inner organisation of the oxygen molecule is a
considerably _plastic_ one. It is readily modified by heat, and these
modifications are