Page:Popular Science Monthly Volume 3.djvu/145

Rh 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. 7, or, as



in most cases, by a bright nucleus, round which sometimes one ring, sometimes several, are disposed in various forms. In Fig. 8 a representation is given of a compound annular nebula, with very elliptic rings and bright nucleus.



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