. 307 



r*> 



When we separate the results of actual observation from 

 those of mere inductive conclusions, in this much disputed 

 question of the existence or non-existence of a self-luminous, 

 vaporous matter in the universe, we find that although the 

 increasing improvements in telescopic vision may, indeed, 

 considerably diminish the number of nebula?, they cannot by 

 any means wholly exhaust them. By the application of in- 

 creasing powers, each new instrument may resolve what the 

 preoeding ones had left unresolved, but it must at the same 

 time, in consequence of its greater powers of penetrating 

 space, replace (at least partially) the resolved nebula? by 

 others not previously reached. 28 A resolution of the older, 

 and the discovery of new nebula?, would therefore follow one 

 another in endless succession, as the fruit of increased optical 

 power. For if we suppose a different result, we must either, 

 according to my view, assume the occupied regions of space 

 to be limited, or that the world-islands, to one of which our 

 system belongs, are so remote from each other that no tele- 

 scopic instrument can ever be invented of sufficient power 

 to penetrate to the confines of any other of these worlds, 

 and that our last or extremest nebula? may resolve themselves 

 into clusters of stars, which, like the stars in the Milky Way, 

 " are projected on a black ground entirely free from vapour."* 

 But can we believe in the probability of a condition of the 

 universe, and of a degree of perfection in optical instruments, 

 in which the entire firmament will no longer exhibit any 

 unresolved nebulous spots ? 



The hypothetical assumption of a self-luminous fluid, ap- 

 pearing, when sharply-defined, in round or oval nebulous spots, 

 must not be confounded with the equally hypothetical assump- 



* Compare Edinburgh Revieiv, vol. Ixxxvii. 1848, p. 186. 

 19 Cosmos, vol. iii. p. 195, and note. 

 TOL. iv. C 



