358 PHILOSOPHICAL TRANSACTIONS. [aNNO 1794, 



they are almost as bright as that belt. The shadow of the ring on Saturn is per- 

 fectly black, like the shadow of Saturn on the ring. The shadow of the ring on 

 Saturn, on each side, is bent a little southwards; so that the apparent curve it 

 makes departs a little from the ring. Also, he tried 5 new concave eye-glasses, 

 but they all proved defective in figure; with one of them, power 36o, he saw 

 the quintuple belt pretty well. With regard to the field of view, they are full 

 as convenient as convex glasses. 



Dr. H. then proceeds to deduce the period of Saturn's rotation from the series 

 of the observations he had made; whence he infers, that, there can remain no 

 doubt about the true quantity of the period in general. He therefore takes a mean 

 of the determinations, which gives 10*^ 16™ 15'. 5 for the approximate rotation 

 of Saturn on its axis. He then adds : 



It now becomes necessary to construct tables for a general calculation of all 

 the observations. For if these should contain descriptions contradicting the cal- 

 culated appearances of the quintuple belt, our assigned period could not be con- 

 sidered as sufficiently established; on the contrary, if the calculated and observed 

 appearances are found to agree, we may rest satisfied that the rotatory motion of 

 this planet, which has so long eluded our strictest attention, is at length obtained. 

 In consequence of a few trials, which were made after the 7th of January, by 

 tables constructed on this mean period, I found that some small correction was 

 required; and obtaining another very good observation on the l6th of the same 

 month, it gave an interval which included 100 revolutions of the equator of 

 Saturn. Now, making the proper deduction for the planet's retrograde motion 

 during the time that passed between the first and last observation, we have from 

 Dec. 4, is'' 46'" 51% to Jan. l6, 8^ 25"' 30% an interval of 42 days IS*" 38™ 

 48', in which the equator of Saturn moved over 35998°.87, from which we 

 compute a period of lO'^ iQ"^ 0^.44. The following table has been constructed 

 on this last period, and in the use of them the complement of the geocentric 

 longitude of Saturn is always to be added, as has been explained in the tables of 

 the satellites of that planet, Phil. Trans, vol. 80. 



