PHYSICAL ASTRONOMY. 549 



time an improved edition was in contemplation ; that .Newton had 

 been pressed by his friends to undertake it, and had refused. 



When Bentley had induced Newton to consent that a new edition 

 should be printed, he announces his success with obvious exultation to 

 Cotes, who was to superintend the work. And in the mean time the 

 Astronomy of David Gregory, published in 1*702, showed in every 

 page how familiar the Newtonian doctrines were to English philos- 

 ophers, and tended to make them more so, as the sermons of Bentley 

 himself had done in 1692. 



Newton's Cambridge contemporaries were among those who took a. 

 part in bringing the Principia before the world. The manuscript 

 draft of it was conveyed to the Royal Society (April 28, 1680) by Dr. 

 Vincent, Fellow of Clare Hall, who was the tutor of Whiston, New- 

 ton's deputy in his professorship ; and he, in presenting the work, spoke 

 of the novelty and dignity of the subject. There exists in the library 

 of the University of Cambridge a manuscript containing the early 

 Propositions of the Principia as far as Prop, xxxiii. (which is a part 

 of Section vii., about Falling Bodies). This appears to have been a 

 transcript of Newton's Lectures, delivered as Lucasian Professor : it is 

 dated October, 1684. 



Is Gravitation proportional to Quantity of Matter ? 



It was a portion of Newton's assertion in his great discovery, that 

 all the bodies of the universe attract each other with forces which are 

 as the quantity of matter in each : that is, for instance, the sun attracts 

 the satellites of any planet just as much as he attracts the planet itself, 

 in proportion to the quantity of matter in each ; and the planets at- 

 tract one another just as much as they attract the sun, according to 

 the quantity of matter. 



To prove this part of the law exactly is a matter which requires care- 

 ful experiments ; and though proved experimentally by Newton, lias 

 been considered in our time worthy of re-examination by the great as- 

 tronomer Bessel. There was some ground for doubt; for the mass of 

 Jupiter, as deduced from the perturbations of Saturn, was only yoV(T 

 of the mass of the sun ; the mass of the same planet as deduced from 

 the perturbations of Juno and Pallas was yoVs" ^ ^at ^ ^ e ^ lln * ^ 

 this difference were to be confirmed by accurate observations and cal- 

 culations, it would follow that the attractive power exercised by Jupi- 

 ter upon the minor planets was: greater than that exercised 



