6l4 PHILOSOPHICAL TRANSACTIONS. [anNO l/QO. 



northern plane of the ring is not, like the belts of Jupiter or those of Saturn, 

 subject to variations of colour and figure; but is most probably owing to some 

 permanent construction of the surface of the ring itself. That however, for 

 instance, this black belt cannot be the shadow of a chain of mountains, may be 

 gathered from its being visible all round on the ring; for at the ends of the ansae 

 there could be no shades visible, on account of the direction of the sun's illumi- 

 nation, which would be in the line of the chain ; and the same argument will 

 hold good against supposed caverns or concavities. It is also pretty evident, that 

 this dark zone is contained between 2 concentric circles, as all the phaenomena 

 answer to the projection of such a zone. Thus, in fig. 4, which was taken May 

 11, 1780, the zone is continued all round the ring, with a gradual decrease of 

 breadth towards the middle answering to the appearance of a narrow circular 

 plane, projected into an ellipsis. 



With regard to the nature of the ring, we may certainly afiirm, that it is no 

 less solid and substantial than the planet itself. The same reasons which prove 

 to us the solidity of the one will be full as valid when applied to the other. 

 Thus we see in fig. 3 and 4, the shadow of the body of Saturn on the ring, 

 which in fig. 3 is eclipsed towards the north, on the following side, and in fig. 

 4 about the middle, according to the opposite situation of the sun. In the same 

 manner we see the shadow ,of the ring cast on the planet, where in fig. 1 and 2 

 we find it on the equatorial part; and May 28, 1780, it was seen towards the 

 south. If we deduce the quantity of matter, contained in the body, from the 

 power by which the satellites are kept in their orbits, and the time of their revolu- 

 tion, it must be remembered, that the ring is included in the result. It is also 

 in a very particular manner evident, that the ring exerts a considerable force on 

 these revolving bodies, since we find them strongly affected with many irregula- 

 rities in their motions, which we cannot properly ascribe to any other cause than 

 the quantity of matter contained in the ring; at least we ought to allow it a 

 proper share in the eflfect, as we do not deny but that the considerable equatorial 

 elevation of Saturn must also join in it. 



The light of the ring of Saturn is generally brighter than that of the planet: 

 for instance, April 19, 1777> the southern part of the ring, which passed before 

 the body, was seen very plainly brighter than the disk of Saturn, on which it 

 was projected; and on the 27th of the same month, with a power of 410, the 

 7-feet reflector had hardly light onough for Saturn, when the ring was sufilciently 

 bright. Again, March 11, 1780, he tried the powers of 222, 332, and 449, 

 successively, and found the light of Saturn less intense than that of the ring; 

 the colour of the body with the high powers turning to a kind of yellow, while 

 that of the ring still remained white. The same result happened on June 25, 

 1781, with the power 460. 



