PREFACE. ix 



tliougli, as I have obfcrvcd *, even the Principles of their 

 own Science cannot be dcmonflrated.by lines and figures. 

 This is to be learned by a man xAio is like Dr. Horfely, not 

 only a Geometer, but aPliilofopher and a Scholar, from a va- 

 luable Work of an antientPhilofopher, upon the Firfl Book of 

 Euclid's Elements ]', as indeed all Works mull be, that are 

 ■written by a man who is both Geometer and Philofopher^ 



The mofc exceptionable part of this Work, and which to 

 fome I am afraid will give much offence, is the laft Book 

 upon Sir Ifaac's Ailronomy. But, iwo, In a Work fuch as 

 this, which treats of the Principles of all things in the Uni- 

 verfe, it was impofiible I could avoid enquiring into the 

 Principle of Motion, the grand Agent in all natural opera- 

 tions, and without which it is impofiible to conceive a ma- 

 terial world ; and my Work would have been exceedingly 

 defeAive, if I had faid nothing of that Principle in the 

 grandefl: and nobleft part of the vifible Creation ; I mean 

 the Celeftial Bodies. But, 2do, It is not the Aftronomy of 

 Sir Ifaac that I find fault with, but the manner of teaching 

 it. The Principia is entirely a Work of Geometry and Aftro- 

 nomy, in which tne Principles of Geometry and Mechanics 

 are wonderfully well applied to the rriotions of the Planets. 

 Now in a Work of this kind, the only purpofe of which was 



* Page 



t The Author is Proclus, an eminent Platonic Philofopher of later times, and who 

 appears to have been as ftudious of Geometry as his mafter Plato. The book is not 

 tranflated, and the printed copy of it very incorreft, fo that it is not to be underftood 

 but by a very good fcholar. See fome Obfervations that I have taken from it. Vol. I, 

 pages 449, 450 j alfo pages 443, 444. 



to 



