VOL. I.] PHILOSOPHICAL TRANSACTIONS. Jfc5 



He confesses that he has not had the opportunity of observing Saturn in his 

 oriental quadrat ; yet he doubts not, but that the shadow appears on the left 

 side, considering that the existence of the ring can be no longer doubted of 

 after so many observations of the shadow cast by Saturn's body upon it, accord- 

 ing as it must happen, following that hypothesis; there being no reason why it 

 should cast the said shadow on one side and not on the other. 



Concerning the observation of Jupiter and his satellites, the famous astrono- 

 mer of Bononia, Cassini, having published, that on the 30th day of July l664, 

 at 2-i- of the clock in the morning, he had observed, with Campani's glasses, that 

 there passed through the broad obscure belt of Jupiter two obscurer spots, by 

 him esteemed to be the shadows of the satellites, moving between Jupiter and 

 the sun, and eclipsing him, and emerging from the western limb. This author 

 first conceived that they were not shadows, but some sallies, or prominencies in 

 that belt; but having been since informed of all the observations made by 

 Cassini and Campani with the new glasses, and seen his figure, he candidly and 

 publicly wishes that he had not spoken of that sally, or prominency ; avow- 

 ing that he can no longer doubt, but that it was the shadow of the satellite 

 between Jupiter and the sun. He hopes also, that in time the shadow of Sa- 

 turn's moon will be seen upon Saturn, although we have yet some years to stay 

 for it, and to prepare also for better glasses. 



From this curious observation, he infers the proportion of the diameter of the 

 satellites to that of Jupiter : and judges, that no longer doubt can be made that 

 these four satellites or moons turn about Jupiter, as our moon turns about the 

 earth, and in the same way as the rest of the celestial bodies of our system move: 

 whence also a strong conjecture may be made, that Saturn's moon turns like* 

 wise about Saturn. 



Hence he also takes occasion to intimate, that we need not scruple to con- 

 clude, that if these two planets have moons wheeling about them, as our earth 

 has one that moves about it, the conformity of these moons with our moon 

 proves the conformity of our earth with those planets, which carrying away their 

 moons with themselves, turn about the sun, and very probably make their moons 

 turn about them in turning themselves about their axis; and also, that there is 

 no cause to invent perplexed and incredible hypotheses, for the receding from 

 this analogy, since, says he, if this be truth, the reason for not publishing this 

 doctrine, which was formerly considered an innovation, will be done away, as 

 one of the most zealous doctors of the contrary opinion has given cause to hope. 



But to return to the matter in hand, this author, upon all these observations 

 and relations of Cassini and Campani, finds no reason to doubt any longer of the 



VOL. I. D 



