XXIV INTRODUCTION. 



of the universe, its structure and motions, al 

 though it must be sedulously studied by all who 

 would become acquainted with physical science, 

 and all who desire to understand the whole of 

 the Principia. 



It has been deemed expedient in giving the pro 

 positions of the First Book, to anticipate in some de 

 gree their application to the motions of the heavenly 

 bodies, which form the subject of the Third. This 

 course was naturally suggested by the circumstance 

 that the greater part of these propositions bear a dis 

 tinct reference to the heavenly motions. But it is 

 truly gratifying to find, as we now do, from Sir D. 

 Brewster s valuable Life of Sir Isaac Newton (one 

 of the most precious gifts ever made both to 

 scientific history and physical science), that the 

 illustrious author himself considered this the best 

 method of teaching the Principia to those not 

 thoroughly conversant with mathematics. Applied 

 to by the celebrated Dr. Bentley, who was desirous 

 of so far understanding the book that he might be 

 able to lecture upon its uses in behalf of Natural 

 Religion, he laid down a plan of reading closely 

 resembling that sketched in the beginning of this 

 Introduction ; recommending that after the earlier 

 propositions of the First Book, the Third should be 

 taken so far as to perceive its scope, and then such 



