▼OL. XVI.] PHILOSOPHICAL TRANSACTIONS. SQ."* 



very close together. But when the ring and the orbits of these satellites are 

 more opeif, there is a greater distance in latitude between this satellite and the 

 ring, and it may be seen both above and below the ansae. 



The second satellite of Saturn, according to the observations hitherto made, 

 is but three quarters of the length of his ring distant from it, and makes its 

 revolution about him in 2 days 17 hours and 43 minutes. After a great number 

 of choice observations, it was concluded that the proportion of the digression 

 of the second, to that of the first, counting both from the centre of Saturn, 

 is as 22 to 17. And the time of the revolution of the second satellite to that 

 of the first, as 244 to 17 ; which is that very same proportion which Kepler 

 observes between the distances and periods of the primary planets, and which 

 we have found to hold among the other satellites of Satui*n, and is also verified 

 in the satellites of Jupiter : which clearly shows the admirable harmony of the 

 particular systems, with the great system of the world. 



Of all the satellites, there are none so near their primary planet, as these 

 two satellites of Saturn, and which, taken both together, make so great a num- 

 ber of conjunctions with their primary in the same space of time ; for there are 

 no less than 653 in a year ; whereas the first two satellites of Jupiter make to- 

 gether, only 617. 



These two satellites were first of all seen March l684, by means of two ex- 

 cellent object glasses, of 100 and 136 feet, and afterwards by two others, of 

 90 and 70 feet, all made by Siguier Campani, after the discovery of the third 

 and fifth satellites, which had been made by others of his glasses, of 47 and 

 34 feet. We made use of them without tubes, by a more simple contrivance 

 than those proposed either before or since. We have since seen all these satel- 

 lites with that of 34 feet, and continued to observe them with glasses of M. 

 Borelli of 40 and 70 feet, and by those which Mr. Artouquel has lately made, 

 of 80, 155 and 220 feet. It was easy to see these two satellites by these dif- 

 ferent sorts of glasses, after having found out the rules of their motion, by 

 which the eye might with more particular attention be directed to the place* 

 where they ought to appear. 



The Radices or Epochce of their Motions, were these: viz. — The first satellite 

 was observed 45 degrees distant from its perigee, moving towards the west, 

 March 1 1, 1686, N.S. at lOh. 40min. at night; and returned to the same po- 

 sition on the 14th of April at the same hour. The second was 36 degrees 

 distant from the perigee to the west, the 30th of March 1686, N.S. at 8 o'clock 

 in the evening. 



By a Comparison of the Revolutions oj" Saturn's Satellites with those of Jupiter. 

 —It appears that the former, in the same order, perform their revolutions in 



