THE SIDEREAL UNIVERSE. 705 



celestial vault. Large spaces seem entirely without them, 

 whilst in other regions they are dispersed like numerous 

 archipelagoes; and the observer can, for instance, particu- 

 larly near the Virgin, see more than 300 traverse the field 

 of the telescope within an hour. 



Although the dispersion of the nebulae apparently does 

 not follow any plan, yet some exact law seems to have pre- 



256. The Crab Nebula: Constellation of the Bull {Taurus). 



sided at their formation, for there are generally very few 

 stars in their vicinity, as if they had drawn towards their 

 centre all the cosmical particles of the regions in which they 

 are placed. Thus Herschel, in his nocturnal explorations, 

 when he saw few stars pass before his instrument, calcu- 

 lated upon a nebula appearing in their place, and was so 

 certain of this that he used to tell his secretaries to be 



