Isaac Newton 
Newton’s Principia; First Book, Sections I., II., III [PDF ebook] 
With Notes and Illustrations, and a Collection of Problems, Principally Intended as Examples of Newton’s Methods

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. I take this opportunity to express my thanks to Mr. Stearn, of King’s College, for his kindness in correcting the errors of the press and for many valuable suggestions.