SPECIAL RESULTS. NEBULJE. 215 



VII. 



THE NEBULAE. WHETHER ALL NEBULA! ARE MERELY REMOTE 



AND VERY DENSE CLUSTERS OF STARS ? - THE TWO 

 MAGELLANIC CLOUDS IN WHICH NEBULSS AND NUME- 

 ROUS CLUSTERS OP STARS ARF. CROWDED TOGETHER. 



THE BLACK PATCHES OR " COAL-SACKs" OF THE SOUTHERN 

 CELESTIAL HEMISPHERE. 



BESIDES the visible celestial bodies which shine with sidereal 

 light, either by their own proper light, or by planetary illu- 

 mination, either isolated, or variously associated forming 

 multiple' stars and revolving round a common centre of 

 gravity, we behold also other forms or masses having 

 a milder, fainter, nebulous, lustre ( 358 ) . These, which are 

 seen in some instances as small disk-shaped luminous clouds 

 having a well-defined outline, whilst in other instances their 

 forms vary greatly, their boundaries are ill-defined, and they 

 are spread over much wider spaces in the sky, appear at 

 the first glance, to the assisted eye which views them through 

 the telescope, to differ altogether from the heavenly bodies 

 which have been treated of in detail in the four preceding 

 sections. As astronomers have been inclined to infer from 

 the observed but hitherto unexplained movements of visible 

 stars ( 359 ) the existence of other unseen celestial bodies, 

 VOL. in. p 



