BOOK VII. 



PHYSICAL ASTRONOMY. 



CHAPTER I. 

 PRELUDE TO NEWTON. 



The Ancients. 



Tj^XPRESSIONS in ancient writers which may be interpreted as in- 

 U dicatiug a notion of gravitation in the Newtonian sense, no doubt 

 occur. But such a notion, we may be sure, must have been in the 

 highest degree obscure, wavering, and partial. I have mentioned 

 (Book i. Chap. 3) an author who has fancied that he traces in the 

 works of the ancients the origin of most of the vaunted discoveries 

 of the moderns. But to ascribe much importance to such expressions 

 would be to give a false representation of the real progress of science. 

 Yet some of Newton's followers put forward these passages as well 

 deserving notice ; and Newton himself appears to have had some 

 pleasure in citing such expressions ; probably with the feeling that 

 they relieved him of some of the odium which, he seems to have ap- 

 prehended, hung over new discoveries. The Preface to the Principia 

 begins by quoting 1 the authority of the ancients, as well as the mod- 

 erns, in favor of applying the science of Mechanics to Natural Phi- 

 losophy. In the Preface to David Gregory's Astronomies Physicce et 

 Geometricce EUmenta, published in 1702, is a large array of names of 

 ancient authors, and of quotations, to prove the early and wide diffu- 

 sion of the doctrine of the gravity of the Heavenly Bodies. And it 

 appears to be now made out, that this collection of ancient authorities 



1 Cum veteres Mechanlcam (uti author est Pappus), iu rerum Naturaliura investi- 

 gatione maximi fecerint, ct recentiores, missis forniis substantialibus et qualitati- 

 bus oceultis, Phenomena Naturae ad leges mathematicas revocare aggressa stint ; 

 visutn est in hoc Tractatu JfaiJicsin excolcrc quatenus ea ad Philosophiam spectat. 



