VOL. LXXX.] PHILOSOPHICAL TRANSACTIONS. ClQ 



planet, its belts, and its figure. April Q, 1775, Dr. H. observed a northern 

 belt on Saturnj which was a little inclined to the line of the ring. May 1, 

 \77^i there was another belt, inclined about 15° to the same line, but it was 

 more to the south, and on the following side came up to the place in which the 

 ring crosses the body. July 13, the belt was again depressed towards the north, 

 almost touching the line where the ring passed behind the body. April 8, 1777, 

 there were 2 fine belts, both a little inclined to the ring. In like manner Dr. 

 H. sets down many other similar observations till near the end of the year 

 1780; and then he adds, it will not be necessary to continue the account of 

 these belts up to the present time ; but that he had constantly observed them, 

 and found them generally in equatorial situations, though now and then they 

 were otherwise. 



We may draw 1 conclusions from what has been reported. The first, which 

 relates to the changes in the appearance of the belts, is, that Saturn has proba- 

 bly a very considerable atmosphere, in which these changes take place ; just as 

 the alterations in the belts of Jupiter have been shown, with great probability, 

 to be in his atmosphere. This has also been confirmed by other observations : 

 thus, in occultations of Saturn's satellites, they seem to hang to the disc a long 

 while before they would vanish. And though we ought to make some allowance 

 for the encroachment of light, by which a satellite is seen to reach up to the 

 disc sooner than it actually does, yet, without a considerable refraction, it could 

 hardly be kept so long in view after the apparent contact. The time of hanging 

 on the disc, in the 7th satellite, has actually amounted to 20 minutes. Now, as 

 its quick motion during that interval carries it through an arch of near 6°, we 

 find that this would denote a refraction of about 1", provided the encroaching of 

 light had no share in the effect. By an observation of the 6th satellite, the re- 

 fraction of Saturn's atmosphere amounts to nearly the same quantity ; for this 

 satellite remained about 14 or 15 minutes longer in view than it should have done; 

 and as it moves about 2^ degrees in that time, and its orbit is larger than that 

 of the 7 th, the difference is inconsiderable. What has been said will suffice to 

 show, that very probably Saturn has an atmosphere of a considerable density. 



The next inference we may draw from the appearance of the belts on Saturn 

 is, that this planet turns on an axis, which is perpendicular to the ring. The 

 arrangement of the belts, during the course of 14 years that Dr. H. had ob- 

 served them, has always followed the direction of the ring, which is what he 

 calls being equatorial. Thus, as the ring opened, the belts began to advance 

 towards the south ; and to show an incurvature answering to the projection of 

 an equatorial line, or to a parallel of the same. When the ring closed up, they 

 returned towards the north ; and are now, while the ring passes over the centre, 



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