In this equation, a dimensional constant G is used to describe the relative strength of gravity. This constant has come to be known as the Newtonian constant of gravitation, though its value was unknown in Newton's lifetime. Not until 1798 was Henry Cavendish able to make the first measurement of G using a torsion balance ; this was widely reported in the press as a measurement of the mass of the Earth since knowing G could allow one to solve for the Earth's mass given the above equation. Newton realized that since all celestial bodies followed the same laws of motion, his law of gravity had to be universal. Succinctly stated, Newton's law of gravitation states that the force on a spherical object of mass m 1 due to the gravitational pull of mass m 2 is F = − − G m 1 m 2 r 2 r ^ ^ , where r is the distance between the two objects' centers of mass and r ^ ^ is the unit vector pointed in the direction away from the center of the first object toward the center of the second object.