IRREGULARITY OF THE PLANET SATURN ] 03 



going observations is the situation of its ring, which passes 



before the planet at the south, but behind at the north. 



The ravs of li^ht therefore, which come to the eye from the owin^o the 



' 5 . . , « , L • it position ot the 



very small remaining southern zone ot the saturman globe, rillg between 



pass at no great distance by the edge of the ring, while those the eye and 



, n -i- ^ ^ tuis region, 



from the north traverse a space clear of every object that 



might disturb their course. If therefore we are in the right 

 to ascribe the observed illusion to an approximate interpo- 

 sition of the ring, we have, in the case under consideration, 

 only two known causes, that can modify light so as to turn 

 it out of its course, which are inflection and refraction. 

 The insufficiency of the first to account for the lifting up 

 of the protuberant small segment of the southern regions 

 will not require a proof. The effects of refraction on the 

 contrary are known to be very considerable. Let us there- 

 fore examine a few of the particulars of the case. The 

 greatest elevation of the visible segment above the ring did 

 not amount to more than one second and three or four 

 tenths. Then supposing the ring, the edge of which is pro- the ring haying 

 bably of an elliptical figure, to have a surrounding atmos- JJ SKm*? 

 phere, it will most likely partake of the same form, and the rays of light 

 rays which pass over its edge will undergo a double refrac- arc ren " acte(i ' 

 tion : the first on their entrance into this atmosphere, and 

 the second at their leaving it, and these refractions seem to 

 be sufficient 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 appear- 

 ance of a different curvature or bulge outwards. 



The refractive power of an atmosphere of the ring has The refractive 

 been mentioned in a former paper*, when the smallest satel- P ower of this , 



t. ^ -. ' t • ill atmosphere aU 



lites of Saturn were seen as it were bisected by the narrow rea dy shown, 

 luminous lines under which form the ring appeared when' 

 the Earth was nearly in the plane of it; and the phenome- 

 non, of which the particulars have now been described, ap- 

 pears to be a second instance in support of the former. 



« See Phil. Tans, for 1790, page 7. 



IV. 



