Figs. 4—8. 



apparent diameter of the moon, and its greatest breadth a little less than half 

 its length. 



It has been conjectured that this, and similar nebulae, are in reality flat cir- 

 cular strata of stars, which are rendered elliptical by projection, being seen in a 

 direction oblique to their plane, and having their diameters foreshortened into 

 the lesser axis of the ellipse. 



In fig. 6, is represented an elliptical spindle-shaped nebula, placed very 

 near that represented in fig. 5. This form of nebulae is very common, and is 

 generally supposed to be produced by an annular mass or ring of stars, which, 

 being seen very obliquely, appears of the elongated form here depicted. Two 

 annular nebulae, seen in directions nearly perpendicular to their planes, and 

 therefore not foreshortened, are represented in fig. 7 and fig. 8. The former 

 is situated between the stars « and & Lyra, and may be seen with a telescope 

 of moderate power. It is well-defined, and is slightly elliptical in its form. 



