388 COSMIC T II ILOSOmY. [WML 



dences are daily coming in to show that there is going on a 

 parallel process of chemical evolution from homogeneity to 

 heterogeneity, which is no less wonderful in its significance. 

 The old empirical classification of stars according to their 

 colours is beginning to have a new meaning. The method of 

 comparison is becoming applicable in astronomy, as it has 

 long been employed in the study of organisms, of societies, 

 and of languages. It begins to be probable that among the 

 various groups of stellar bodies there may be found cosmica] 

 matter in many different stages of evolution, — from the pri- 

 mitive nebula which yields but .a simple hydrogen-line, to 

 such a highly-evolved body as our own sun with the many- 

 lined vapour of iron abundant in its heated atmosphere. 

 But into this fascinating region of speculation it would 

 be somewhat premature for us now to enter. Merely 

 indicating what a rich harvest of discovery is here likely 

 to reward the labourers of the immediate future, I would 

 call attention to an interesting speculation of Mr. Spencer's, 

 the possible inadequacy of which need not weaken the 

 effect of the evidence above cited from planetary phe- 

 nomena, and which is in every way worthy of serious 

 consideration. 



According to Mr. Spencer, the distribution of nebulse 

 affords a significant illustration of the nebular hypothesis. 

 Speaking generally, nebulas occur in regions where developed 

 stars are scarce. The vast groups of spherical nebulae, here 

 and there partly developed into starry clusters, which con- 

 stitute the so-called Magellanic Clouds, are situated in a 

 district of the sky that is otherwise starless. Now by far 

 the most striking of this class of facts is one which serves to 

 bring the entire sidereal system into direct comparison with 

 that little portion of it to which we belong. Just as the 

 planets lie almost entirely in a single plane, so the stars are 

 distributed in almost infinite numbers in the plane of the 

 Milky Way, while elsewhere thev occur rarely. And just 



