Experiments to Determine the Density of the Earth (1798): Henry Cavendish’s heroic struggle for precision as he improves John Michell’s apparatus such that for the first time he is able to measure the gravitational constant exactly. For that he measures the minuscule attraction of two weights. From this he calculates the gravitational force per mass and such is able to calculate (“weigh”) the earth’s mass and incidentally of all parts of the solar system.