made with a view to investigate its Magnitude , &c_ 16*3 
tenths. Then supposing the ring, the edge of which is pro- 
bably of an elliptical figure, to have a surrounding atmosphere, 
it will most likely partake of the same form, and the rays 
which pass over its edge will undergo a double refraction : 
the first on their entrance into this atmosphere, and the se- 
cond at their leaving it, and these refractions seem to be suf- 
ficient to produce the observed elevation. For should they 
raise the protuberant appearance only half a second, or even 
less, the segment could no longer range with the rest of the 
globe of Saturn, but must assume the appearance of a different 
curvature or bulge outwards. 
The refractive power of an atmosphere of the ring has 
been mentioned in a former paper,* when the smallest satel- 
lites of Saturn were seen as it were bisected by the narrow' 
luminous line under which form the ring appeared when the 
earth was nearly in the plane of it; and the phenomenon, of 
which the particulars have now been described, appears to be 
a second instance in support of the former. 
* See Phil. Trans, for 1790, page 7, 
