A HISTORY OF SCIENCE 



"Con. i. There is, therefore, a power of gravity 

 tending to all the planets ; for doubtless Venus, Mer- 

 cury, and the rest are bodies of the same sort with 

 Jupiter and Saturn. And since all attraction (by 

 Law iii.) is mutual, Jupiter will therefore gravitate 

 towards all his own satellites, Saturn towards his, the 

 earth towards the moon, and the sun towards all the 

 primary planets. 



"CoR. 2. The force of gravity which tends to any 

 one planet is reciprocally as the square of the distance 

 of places from the planet's centre. 



"CoR. 3. All the planets do mutually gravitate 

 towards one another, by Cor. i and 2, and hence it is 

 that Jupiter and Saturn, when near their conjunction, 

 by their mutual attractions sensibly disturb each 

 other's motions. So the sun disturbs the motions of 

 the moon; and both sun and moon disturb our sea, 

 as we shall hereafter explain. 



"The force which retains the celestial bodies in their 

 orbits has been hitherto called centripetal force; but 

 it being now made plain that it can be no other than a 

 gravitating force, we shall hereafter call it gravity. 

 For the cause of the centripetal force which retains the 

 moon in its orbit will extend itself to all the planets by 

 Rules i., ii., and iii. 



" PROPOSITION VI., THEOREM VI. 



" That all bodies gravitate towards every planet; and 

 that ike weights of ike bodies towards any the same planet, 

 at equal distances from the centre of the planet, are t>ro- 



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