Principia

The Philosophiæ Naturalis Principia Mathematica, also known simply as the Principia, was a book by Isaac Newton which explained his theory of gravity. It was published on 5 July, 1687. (PROSE: Time Traveller's Diary, Newtons Sleep)

As a young boy, Newton encountered an angel which showed him his future, in which he remembered writing the Principia. (PROSE: Newtons Sleep)