**Chronology of Gravitational Physics and Relativity**

1640 | Ismael Bullialdus suggests an inverse-square gravitational force law. |

1665 | Isaac Newton deduces the inverse-square gravitational force law from the "falling'' of the Moon. |

1684 | Isaac Newton proves that planets moving under an inverse-square force law will obey Kepler's laws. |

1686 | Isaac Newton uses a fixed length pendulum with weights of varying composition to test the weak equivalence principle to 1 part in 1000. |

1798 | Henry Cavendish measures the gravitational constant. |

1845 | Urbain Leverrier observes a 35'' per century excess precession of Mercury's orbit. |

1876 | William Clifford suggests that the motion of matter may be due to changes in the geometry of space. |

1882 | Simon Newcomb observes a 43'' per century excess precession of Mercury's orbit. |

1887 | Albert Michelson and Edward Morley do not detect the ether drift. |

1889 | Roland von Eotvos uses a torsion fiber balance to test the weak equivalence principle to 1 part in one billion. |

1893 | Ernst Mach states Mach's principle; first constructive attack on the idea of Newtonian absolute space. |

1905 | Albert Einstein completes his theory of special relativity and states the law of mass-energy conservation. |

1907 | Albert Einstein introduces the principle of equivalence of gravitation and inertia and uses it to predict the gravitational redshift, |

1915 | Albert Einstein completes his theory of general relativity. |

1916 | Albert Einstein shows that the field equations of general relativity admit wavelike solutions. |

1918 | J. Lense and Hans Thirring find the gravitomagnetic precession of gyroscopes in the equations of general relativity. |

1919 | Arthur Eddington leads a solar eclipse expedition which claims to detect gravitational deflection of light by the Sun. |

1921 | T. Kaluza demonstrates that a five-dimensional version of Einstein's equations unifies gravitation and electromagnetism. |

1937 | Fritz Zwicky states that galaxies could act as gravitational lenses. |

1937 | Albert Einstein, Leopold Infeld, and Banesh Hoffman show that the geodesic equations of general relativity can be deduced from its field equations. |

1957 | John Wheeler discusses the breakdown of classical general relativity near singularities and the need for quantum gravity. |

1960 | Robert Pound and Glen Rebka test the gravitational redshift predicted by the equivalence principle to approximately 1%. |

1962 | Robert Dicke, Peter Roll, and R. Krotkov use a torsion fiber balance to test the weak equivalence principle to 2 parts in 100 billion. |

1964 | Irwin Shapiro predicts a gravitational time delay of radiation travel as a test of general relativity. |

1965 | Joseph Weber puts the first Weber bar gravitational wave detector into operation. |

1968 | Irwin Shapiro presents the first detection of the Shapiro delay. |

1968 | Kenneth Nordtvedt studies a possible violation of the weak equivalence principle for self-gravitating bodies and proposes a new test of the weak equivalence principle based on observing the relative motion of the Earth and Moon in the Sun's gravitational field. |

1976 | Robert Vessot and Martin Levine use a hydrogen maser clock on a Scout D rocket to test the gravitational redshift predicted by the equivalence principle to approximately 0.007%. |

1979 | Dennis Walsh, Robert Carswell, and Ray Weymann discover the gravitationally lensed quasar Q0957+561. |

1982 | Joseph Taylor and Joel Weisberg show that the rate of energy loss from the binary pulsar PSR1913+16 agrees with that predicted by the general relativistic quadrupole formula to within 5%. |