THE CONSTITUTION OF NEBULJE. 



135 



into the simple or compound annular nebula of a type which is given 

 in Fig. 7. 



The space within most of these elliptie rings is not perfectly dark, 

 but is occupied either by a diffused nebulous light, as in Fig. 1, or, as 



Fig. 9. 



Elliptical Annulab Nebula. 



in most cases, by a bright nucleus, round which sometimes one ring, 

 sometimes several, are disposed in various forms. In Fig. 8 a represen- 

 tation is given of a compound annular nebula, with very elliptic rings 

 and bright nucleus. 



Pig. 10. 



Elongated Nebula. 



According as the ring has its surface or its edge turned toward us, 

 or according as our line of sight is perpendicular or more or less 

 obliquely inclined to the surface of the ring, its form approaches that 



