Philosophiæ Naturalis Principia Mathematica
From RationalWiki
The Philosophiæ Naturalis Principia Mathematica (Mathematical principles of natural philosophy) is Isaac Newton's bestselling 1687 book which contains the Laws of Motion, the Law of Universal Gravitation, and a theoretic derivation of Kepler's Law.
It's also known as Principia Mathematica or Principia, because the real name is too long. It is not to be confused with the Principia Mathematica by Russell and Whitehead, which you also haven't read.