It was Isaac Newton's Principia that founded the law of universal gravitation on 5th July 1687. It is the same principia that inspired Albert Einstein into formulating the Einstein field equations (the general relativity theory). It is still the same principia, I believe, will lead us to the quantum theory of gravity (Quantum gravity)

According to Newton’s Principia, the force of gravity governs the movement of bodies in the solar system. It is this simple mathematical law which determines the motion of bodies. The force of gravity accurately predicts the planetary orbits, it was used to put the first man on the moon, it predicts the return of comets, the rotation of galaxies, the solar eclipses, artificial satellites, satellite communications and television, the GPS and interplanetary probes. I almost forgot, it is why NASA was established in the first place.

The book has an active table of contents for readers to access each chapter,

LIFE OF SIR ISAAC NEWTONxiv
BOOK I.1
THE MATHEMATICAL PRINCIPLES OF NATURAL PHILOSOPHY.1
AXIOMS, OR LAWS OF MOTION.20
OF THE MOTION OF BODIES.43
SECTION II.65
Of the Invention of Centripetal Forces.65
SECTION III.91
Of the motion of bodies in eccentric conic sections.91
SECTION IV.110
Of the finding of elliptic, parabolic, and hyperbolic orbits, from the focus given.110
SECTION V.123
How the orbits are to be found when neither focus is given.123
SECTION VI.171
How the motions are to be found in given orbits.171
SECTION VII.183
Concerning the rectilinear ascent and descent of bodies.183
SECTION VIII.202
Of the invention of orbits wherein bodies will revolve, being acted upon by any sort of centripetal force.202
SECTION IX.212
Of the motion of bodies in moveable orbits; and of the motion of the apsides.212
SECTION X.230
Of the motion of bodies in given superficies, and of the reciprocal motion of funependulous bodies.230
SECTION XI.255
Of the motions of bodies tending to each other with centripetal forces.255
SECTION XII.300
Of the attractive forces of sphærical bodies.300
SECTION XIII.333
Of the attractive forces of bodies which are not of a sphærical figure.333
SECTION XIV.353
Of the motion of very small bodies when agitated by centripetal forces tending to the several parts of any very great body.353
BOOK II.365
OF THE MOTION OF BODIES.365
SECTION I.365
Of the motion of bodies that are resisted in the ratio of the velocity.365
SECTION II.381
Of the motion of bodies that are resisted in the duplicate ratio of their velocities.381
SECTION III.421
Of the motions of bodies which are resisted partly in the ratio of the velocities, and partly in the duplicate of the same ratio.421
SECTION IV.436
Of the circular motion of bodies in resisting mediums.436
SECTION V.449
Of the density and compression of fluids; and of hydrostatics.449
SECTION VI.469
Of the motion and resistance of funependulous bodies.469
SECTION VII.507
Of the motion of fluids, and the resistance made to projected bodies.507
SECTION VIII.571
Of motion propagated through fluids.571
SECTION IX.600
Of the circular motion of fluids.600
BOOK III.619
RULES OF REASONING IN PHILOSOPHY.621
PHÆNOMENA OR APPEARANCES.625
PROPOSITIONS634
OF THE MOTION OF THE MOON'S NODES.724
END OF THE MATHEMATICAL PRINCIPLES.863
THE SYSTEM OF THE WORLD.865