Cavendish Experiment - Did Cavendish Determine G?

Did Cavendish Determine G?

The formulation of Newtonian gravity in terms of a gravitational constant did not become standard until long after Cavendish's time. Indeed, one of the first references to G is in 1873, 75 years after Cavendish's work. Cavendish expressed his result in terms of the density of the Earth, and he referred to his experiment in correspondence as 'weighing the world'. Later authors reformulated his results in modern terms. thus:

After converting to SI units, Cavendish's value for the Earth's density, 5.448 g cm−3, gives

G = 6.74 × 10−11 m3 kg−1 s−2,

which differs by only 1% from the currently accepted value: 6.67428 × 10−11 m3 kg−1 s−2.

For this reason, historians of science have argued that Cavendish did not measure the gravitational constant.

Physicists, however, often use units where the gravitational constant takes a different form. The Gaussian gravitational constant used in space dynamics is a defined constant, and the Cavendish experiment can be considered as a measurement of the astronomical unit. In Cavendish's time, physicists used the same units for mass and weight, in effect taking as a standard acceleration. Then, since was known, played the role of an inverse gravitational constant. The density of the Earth was hence a much sought-after quantity at the time, and there had been earlier attempts to measure it, such as the Schiehallion experiment in 1774.

For these reasons, physicists generally do credit Cavendish with the first measurement of the gravitational constant.