Why did Cavendish and Michell not originally describe their experiment as measuring G?

Henry Cavendish and John Michell did not describe their experiment as a measurement of the gravitational constant (G) because that specific formulation of Newton’s law of universal gravitation did not exist during their time. The mathematical expression involving G was not developed until the late 19th century.12

Instead, the experiment was originally devised by John Michell and later performed by Henry Cavendish for the express purpose of determining Earth’s mean density. By measuring the gravitational attraction between lead spheres using a torsion balance, Cavendish was able to calculate the density of the planet relative to water. It was only in later years that this data was used to derive the value of G as it is understood in modern physics.12