J18 PHILOSOPHICAL TRANSACTIONS. [aNNO 1792, 



at a division of the ring of Saturn, it was highly necessary to express that sur- 

 mise witli proper doubts concerning the reality of so wonderful a construction ; 

 but his late views of its southern plane, assisted by some conclusions drawn from 

 the discovery of the quick rotation of the ring, have enabled him to speak, de- 

 cisively on this subject. His suspicion of a divided or double ring arose chiefly 

 from the following circumstances. 



In the first place, the black belt, during the time of about 10 years observa- 

 tion, on the northern plane, was subject to no kind of change ; but remained 

 always permanently of the same breadth and colour. With regard to its breadth, 

 it is true that it could only be judged of in that part of it which goes across the 

 body of the planet, by the rules of perspective, which made Dr. H. suppose it to 

 be as broad there as it was on the two sides ; yet now, as we know that the ring 

 revolves in about lOi hours, it is very certain that the apparently narrow part 

 across the body, and that which was hidden behind the planet, in the course of 

 an evening, when he had been observing Saturn for many hours together, must 

 have been exposed to view in their full breadth, on the sides of the ring ; and that 

 if there had been any dilFerence, he must have perceived it ; especially as he was 

 continually on the look out for such phenomena, by way of ascertaining, if pos- 

 sible, the rotation of the ring. 



In the next place, the colour of this dark belt was also uniformly the same, 

 whenever he observed it under equally favourable circumstances ; and being so 

 well defined on both its borders, and, in every part of the revolving ring, present- 

 ing us with the same view of colour, breadth, and sharpness of its outlines, no kind 

 of hypothesis but a division of the ring, through which the open heavens may be 

 seen, will answer the conditions of this phenomenon. It remained therefore only 

 to ascertain, whether the southern plane would present us with the same aspect. 

 And since Dr. H. had lately a great number of fine views of the ring of Saturn, 

 he here delivers as many of the observations as will be sufficient to throw light 

 enough on the subject, to enable us to decide the question, whether this ring be 

 double or single ? 



Observations on the Ring of Saturn. — Sept. 7, 1790; 20-feet reflector. No 

 dark division can as yet be seen on the ring of Saturn ; but it is hardly open 

 enough to expect it to be visible. — Aug. 5, 1791 ; 20-feet reflector. The black 

 list, on this side of the ring of Saturn, is exactly in the same relative place where 

 it was seen on the northern plane. — Sept. 25, 1791 ; 20-feet reflector. The 

 black division goes all around the ring, as far as he can trace it, exactly in the 

 same place where he used to see it on the north side. — Oct. 13, 179^ 5 10-feet 

 reflector. The black division on the southern plane of Saturn's ring is in the 

 same place, of the same breadth, and at the same distance from the outer edge, 

 that he had always seen it on the northern plane. With a power of 400, he saw 



