VOL. I.] PHILOSOPHICAL TRANSACTIONS. 101 



according to the complication of their several motions, will' somewhat change the 

 position of Jupiter as to that common centre of gravity of all these bodies ; 

 which yet, because of their smallness, may chance to be so little, as that, at this 

 distance, the change of this apparent place may not be discernible. And what 

 is said of Jupiter is in the like manner to be understood of Saturn and his 

 satellite, discovered by Huygens : For all these satellites are to their principals as 

 so many moons to the earth. And I do very well remember, in the letters be- 

 fore cited, Mr. Horrocks expresses some such little inequalities in Saturn's mo- 

 tion, of which he could not imagine what account to give, as if (to use his ex- 

 pression) this crabbed old Saturn had despised his youth. Which for aught I 

 know might well enough have been accounted for, if at that time the satellite 

 of Saturn had been discovered, and that Mr. Horrocks had thought of such a 

 notion as the common centre of gravity of Saturn and his companion, to be 

 considerable as to the guiding of his motion. 



You have now, in obedience to your commands, an account of my thoughts 

 as to this matter, though yet immature and unpolished : What use you will 

 please to make of them I shall leave to your prudence, &c. 



All Appendix, written hy Way of Letter to the Publisher, being an 

 Answer to some Objections made by several Persons to the preceding 

 Discourse. N° 16, p. 281. 



I received yours, and am very well contented that objections be made against 

 my hypothesis concerning tides : being proposed but as a conjecture to be 

 examined ; and upon that examination rectified, if there be occasion ; or re- 

 jected if it will not hold water. 



1 . To the first objection of those you mention, That it appears not how two 

 bodies that have no tie can have one common centre of gravity ; that is, for so 

 I understand the intendment of the objection, can act or be acted in the same 

 manner as if they were connected : I shall only answer, that it is harder to 

 show how they have than that they have it. That the loadstone and iron have 

 somewhat equivalent to a tie, though we see it not, yet by the effects we know. 

 And it would be easy to show that two loadstones at once applied in different 

 positions to the same needle, at some convenient distance, will draw it, not to 

 point directly to either of them, but to some point between both ; which point 

 is, as to those two, the common centre of attraction; and it is the same as if 

 some one loadstone were in that point. Yet have these two loadstones no 

 connection or tie, though a common centre of virtue, according to which they 

 jointly act. And as to the present case, how the earth and moon are connect- 



