What was the original purpose of the Cavendish experiment?

The original purpose of the Cavendish experiment was to determine the density of Earth.12

It is a common misconception that Henry Cavendish and his contemporary John Michell designed the experiment to measure the gravitational constant (G). In fact, the formulation of Newton’s law of universal gravitation involving G did not occur until the late 19th century, long after the experiment was performed in 1797–98.1

By using a torsion balance to measure the incredibly weak gravitational attraction between lead spheres, Cavendish was able to calculate Earth’s mean density as 5.48 times that of water. This result was remarkably accurate, falling within 1 percent of the modern accepted value. The experiment also served to demonstrate that Newton’s law of gravitation holds true on scales much smaller than those of the solar system.12