PHYSICAL ASTRONOMY. 



\v;is supplied to (Jivgory by Newton himself. The late Professor Jii- 

 gaud, in his Historical Essay on the First Publication of Sir Isaac 

 Newton's Principia, says (pp. 80 and 101) that having been allowed 

 to examine Gregory's papers, he found that the quotations given by 

 him in his Preface are copied or abridged from notes which Newton 

 had supplied to him in his own handwriting. Some of the most no- 

 ticeable of the quotations are those taken from Plutarch's Dialogue 

 on the Face which appears in the Moon's Disk : it is there said, for 

 example, by one of the speakers, that the Moon is perhaps prevented 

 from falling to the earth by the rapidity of her revolution round it ; 

 as a stone whirled in a sling keeps it stretched. Lucretius also is 

 quoted, as teaching that all bodies would descend with an equal ce- 

 lerity in a vacuum : 



Omnia quapropter debent per inane quietum 

 uEque ponderibus non sequis concita ferri. 



Lib. ii. v. 233. 



It is asserted in Gregory's Preface that Pythagoras was not unac- 

 quainted with the important law of gravity, the inverse squares of the 

 distances from the centre. For, it is argued, the seven strings of 

 Apollo's lyre mean the seven planets ; and the proportions of the 

 notes of strings are reciprocally as the inverse squares of the weights 

 which stretch them. 



I have attempted, throughout this work, to trace the progress of the 

 discovery of the great truths which constitute real science, in a more 

 precise manner than that which these interpretations of ancient au- 

 thors exemplify. 



Jeremiah Horrox. 



In describing the Prelude to the Epoch of Newton, I have spoken 

 (p. 395) of a group of philosophers in England who began, in the first 

 half of the seventeenth century, to knock at the door where Truth 

 was to be found, although it was left for Newton to force it open ; 

 and I have there noticed the influence of the civil wars on the prog- 

 ress of philosophical studies. To the persons thus tending towards 

 the true physical theory of the solar system, I ought to have added 

 Jeremy Horrox, whom I have mentioned in a former part (Book v. 

 chap. 5) as one of the earliest admirers of Kepler's discoveries. He 

 died at the early age of twenty-two, having been the first person who 

 ever saw Venus pass across the disk of the Sun according to astro- 

 nomical prediction, which took place in 1G39. His Venus in sole visa. 

 VOL. I. 35 



