VOL. VIII.] PHILOSOPHICAL TRANSACTIONS. 53 



of the first with the second, made us seclude the period of 2-^ days. We there- 

 fore judged, by these observations, that this last planet finishes its revolution 

 about Saturn in 4 -J- days; that the semidiameter of this circle is three semidia- 

 meters and a fourth of Saturn's ring; and that it was towards its greatest west- 

 ward digression the 23d of Dec. and Jan. 1, about 7 in the evening. 



On these grounds, after the 4th observation, we made an epheineris of this 

 planet, which has served us since, until the occultation of Saturn, without having 

 found any other difference in the observations, but that, as for the nearest 

 planet, the return to the same place, after one revolution of 4-.^- days, is made 

 one hour later, so that one circuit is finished in 4 days and 13 hours. We 

 have also learned by the following observations, that when the interior satellite 

 is much distant from its great digressions, it has some southern latitude in re- 

 spect to the line of the wings in the upper semicircle, and some northern lati- 

 tude in the inferior; as has also the old satellite, which has more of it in propor- 

 tion to the diameter of its circle. 



Our application to observe the planet nearest to Saturn, in the small time we 

 had at evenings, by reason of his proximity to the sun beams, had diverted us 

 from the other more remote planet. But Feb. 6, we began fo see it again, and 

 the weather favoured us well enough to observe it almost all the days following, 

 until the 20th of Feb. except the 9th and 18th. It was conveniently seen by 

 Campani's telescope of 17 feet, by which the first discovery of it had been 

 made ; and by another of 20 feet, made by Lebas, with which Mr. Picard ob- 

 served it also constantly, and sometimes in the company of Mr. Huygens and 

 Mr. Mariotte. The first observations of the distances were made by an estimate 

 of the eye, comparing the exterior satellite with Saturn and with the other 

 satellites. The last were made by the measure of the time between the passage 

 of the planet, and that of the centre of Saturn. This new planet more and 

 more removed from Saturn till the Qth of Feb. when we measured the difference 

 between its passage and that of the centre of Saturn, and found it 30 sec. of 

 an hour, which give at least 10 diameters of Saturn; but on the 20th, it was 

 already too near the beams of the sun to measure its distance; which yet by 

 estimate was judged greater than it had been the 1 Qth. 



By the apparent swiftness of its motion during the first days, it is easy to see, 

 that this planet had been seen in conjunction with Saturn Feb. 3 ; and by its 

 motion on the west it appears, that it was in the inferior part of its circle: and 

 because, during this time of 17 days, it removed more and more from Saturn, it 

 is certain that it remained in the same quadrant of the inferior western circle 

 above 17 days, and that its whole time of revolution is more than 68 days. It 

 was these last days a,t a distance almost equal to that which it had about the end 



