It was only in the 80’s, after thousands of observations of the spectra
of stars, nebulæ, and comets had been secured, that the full meaning of
the revelations of the spectroscope began to dawn upon the world.
Before the introduction of spectrum analysis all stars were supposed
to be suns, and the only difference recognized among them was one of
brilliancy and the variation of brilliancy in the case of some of them.
It ultimately came out that great classes might be recognized by
the differences of their spectra, which were ultimately traced to
differences in their chemistry and in their temperature, as determined
by the extension of the spectra in the ultra-violet, the whiter stars
being hotter than the red ones, as a white-hot poker is hotter than a
red-hot poker.
Next there was evidence to show that a large proportion of the stars
were not stars at all like the sun, but swarms of meteorites; and in
this way the mysterious new stars which appear from time to time in
the heavens, and a large number of variable stars, were explained as
arising from collisions among such swarms.
The inquiry which dealt with the spectroscopic results, having thus
introduced the ideas of meteor swarms and collisions to explain many
stellar phenomena, went further and showed that the various chemical
changes observed in passing from star to star might also be explained
by supposing the whole stellar constitution to arise from cool
meteoritic swarms represented by nebulæ, the changes up to a certain
point being explained by a rise of temperature due to condensation
towards a centre. Here the new view was opposed to that of Laplace,
advanced during the last century, that the stars were produced by
condensation and cooling; but Kelvin had shown, before the new view
was enunciated, that Laplace’s view was contrary to thermodynamics,
a branch of science which had developed since Laplace published his
famous _Exposition du Système du Monde_.
After all the meteorites in the parent swarm had been condensed into
the central gaseous mass, that mass had to cool. So that we had in
the heavens not only stars more or less meteoritic in structure,
of _rising_ temperature, but stars chiefly gaseous, of falling
temperature. It was obvious that representatives of both these classes
of stars might have nearly the same mean effective temperature, and
therefore more or less the same spectrum. A minute inquiry entirely
justified these conclusions.
So far had the detailed chemistry of the stars been carried in the
latter years of the century that the question of stellar evolution gave
rise to that of inorganic evolution generally, the sequence in the
phenomena of which can only be studied in the stars, for laboratory
work without stint has shown that in them we have celestial furnaces,
the heat of which transcends that of our most powerful electric sparks.
In this way astronomy is paying the debt she owes to chemistry.