164 PIONEERS OF EVOLUTION PART 



while the photographic plate is a scarcely less impor- 

 tant witness. The one has demonstrated that many 

 nebulae, once thought to be star-clusters, are masses 

 of glowing hydrogen and nitrogen gases ; that, to 

 quote the striking communication made by the 

 highest authority on the subject, Sir William Huggins, 

 in his Presidential Address to the British Association, 

 1891, 'in the part of the heavens within our ken, 

 the stars still in the early and middle stages of 

 Evolution exceed greatly in number those which 

 appear to be in an advanced condition of condensa- 

 tion/ The other, recording infallible vibrations on 

 a sensitive plate, and securing accurate registration 

 of the impressions, reveals, as in Dr. Roberts's 

 grand photograph of the nebula in Andromeda, a 

 central mass round which are distinct rings of 

 luminous matter, these being separated from the 

 main body by dark rifts or spaces. To quote Sir W. 

 Huggins once more, ' We seem to have presented to 

 us some stage of cosmical evolution on a gigantic 

 scale/ 



The great fact that lies at the back of all these 

 confirmations of the nebular theory is the funda- 

 mental identity of the stuff of which the universe is 

 made ; a fact which entered into the prevision of the 

 Ionian cosmologists. Sir W. 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 the late Lord Salisbury's 

 Presidential Address to the British Association, 1894, 



