VOL. LXXXII.] PHILOSOPHICAL TRANSACTIONS. IIQ 



it very distinctly ; it is of the same kind of colour as the space between the ring 

 and the body, but not so dark. — Oct. 24, 1791 ; 7-feet reflector. With a new, 

 machine-polished, most excellent speculum, he saw that the division on the ring 

 of Saturn, and the open spaces between the ring and the body, are equally dark, 

 and of the same colour with the heavens about the planet. 20-feet reflector. The 

 black division on the ring was as dark as the heavens. It was equally broad on 

 both sides of the ring. With a 40-feet reflector, he saw the division on the ring 

 of Saturn of the same colour as the surrounding heavens. It was an equal breadth 

 on both sides, and he could trace it a great way towards the body of Saturn. 

 With a 20-feet reflector, and power of 600, he could trace the division very 

 nearly as far as the place, where a perpendicular to the direction of the ring would 

 divide the open space between the planet and the ring into 2 equal parts. 



From these observations, added to what has been given in some former papers. 

 Dr. H. thinks himself authorized now to say, that the planet Saturn has 2 con_ 

 centric rings, of unequal dimensions and breadth, situated in one plane, which is 

 probably not much inclined to the equator of the planet. These rings are at a 

 considerable distance from each other, the smallest being much less in diameter 



at the outside, than the largest is parts. 



i. 1.1. • •j„ T'U^ j'.„^„o;^„ Inside diameter of the smaller rinar 6900 



at the mside. The dimension Outside diameter ^. 7^10 



of the two rings and the in- Inside diameter of the larger ring 7740 



termediate space are nearly in Outside diameter 8300 



t' J Breadth ot tlie mner ring 805 



the annexed proportion to each Breadth of the outer ring 280 



ju Breadth of the vacant space 115 



Admitting, with M. de la Lande, that the breadth of the whole ring, as for- 

 merly supposed to consist of one entire mass, is near -i- of the diameter of Saturn, 

 it follows that the vacant space between the 2 rings, according to the above state- 

 ment, amounts to near 2513 miles. It may be remarked, that this opening in 

 the ring must be of considerable service to the planet, in reducing the space that 

 is eclipsed by the shadow of the ring to a much smaller compass; both on account 

 of the direct light it lets through, and because there will be a strong reverberation 

 of the rays of the sun between the two opposit.e edges. And if these rings should 

 be surrounded by some atmosphere, which is highly probable, the refractions 

 that will take place on the edges will still contribute to lessen the darkness which 

 the shadow of an undivided ring would have occasioned. 



As we have now admitted Saturn to have 2 rings entirely detached from each 

 other, so as plainly to permit us to see the open heavens through the vacancy 

 between them; and as in a former paper Dr. H. had given the revolution of the 

 ring, which was then supposed to be all in one united mass, it will be necessary 

 to examine, whether both rings partake in the same revolution, or to which the 

 period which has been assigned belongs ? To decide this point, we must recur 



