736 THE UNIVERSE. 



the Crab nebula, an animal of which its singular form 

 puts one in mind. 



The nebulae mark the limits of sidereal investigation. 

 In proportion as with our new means we extend our 



323. Sijiral Nebula of the Constellation of the Greyhounds {Canes Venatici], 



researches further into the starry sphere, we find new 

 luminous bodies of this class. But in the extreme depth 

 of the heavens there are still a certain number which 

 cannot be resolved. 



Already 4500 nebulae are known. They are scattered 

 through both hemispheres, and the least of them consists 



