It was now some thirty years since the spectroscope gave us for the
first time certain knowledge of the nature of the heavenly bodies, and
revealed the fundamental fact that terrestrial matter is not peculiar
to the solar system, but is common to all the stars which are visible
to us. Professor Rowland had since shown us that if the whole earth
were heated to the temperature of the sun, its spectrum would resemble
very closely the solar spectrum. In the nebulæ, the elder Herschel saw
portions of the fiery mist or "shining fluid," out of which the
heavens and the earth had been slowly fashioned. For a time this view
of the nebulæ gave place to that which regarded them as external
galaxies--cosmical "sand heaps," too remote to be resolved into
separate stars, though, indeed, in 1858, Mr. Herbert Spencer showed
that the observations of nebulæ up to that time were really in favor
of an evolutional progress. In 1864 he (the speaker) brought the
spectroscope to bear upon them; the bright lines which flashed upon
the eye showed the source of the light to be glowing gas, and so
restored these bodies to what is probably their true place, as an
early stage of sidereal life. At that early time our knowledge of
stellar spectra was small. For this reason partly, and probably also
under the undue influence of theological opinions then widely
prevalent, he unwisely wrote in his original paper in 1864, that "in
these objects we no longer have to do with a special modification of
our own type of sun, but find ourselves in presence of objects
possessing a distinct and peculiar plan of structure." Two years
later, however, in a lecture before this association, he took a truer
position. "Our views of the universe," he said, "are undergoing
important changes; let us wait for more facts with minds unfettered by
any dogmatic theory, and, therefore, free to receive the teaching,
whatever it may be, of new observations."