The great fact that lies at the back of all these confirmations of the nebular theory is the fundamental identity of the stuff of which the universe is made; a fact which entered into the prevision of the Ionian cosmologists. Dr. Huggins says that "if the whole earth were heated to the temperature of the sun, its spectrum would resemble very closely the solar spectrum." In referring to this, there may be carrying of "owls to Athens," but that re-statements may sometimes be needful has illustration in Lord Salisbury's Presidential Address to the British Association, 1894, wherein the assumed absence of oxygen and nitrogen in the sun's spectrum is adduced as an argument against the theory of the common origin of the bodies of the solar system. Speaking of the predominant proportion of oxygen in the solid and liquid substances of the earth, and of the predominance of nitrogen in our atmosphere, his lordship asked, "if the earth be a detached bit whisked off the mass of the sun, as cosmogonists love to tell us, how comes it that, in leaving the sun, we cleaned him out so completely of his nitrogen and oxygen that not a trace of these gases remains behind to be discovered even by the searching vision of the spectroscope?" If Lord Salisbury had consulted Dr. Huggins, or some foreign astronomer of equal rank, as Dunér or Scheiner, he would not have put a question exposing his ignorance, and unmasking his prejudice. These authorities would have told him that when a mixture of the incandescent vapours of the metals and metalloids (or non-metallic elementary substances, to which class both oxygen and nitrogen belong), or their compounds, is examined with the spectroscope, the spectra of the metalloids always yield before that of the metals. Hence the absence of the lines of oxygen and other metalloids, carbon and silicon excepted, among the vast crowd of lines in the solar spectrum. Then, too, in extreme states of rarefaction of the sun's absorbing layer, the absorption of the oxygen is too small to be sensible to us.