How did the lead spheres in the Cavendish experiment attract one another?

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The lead spheres in the Cavendish experiment attracted one another through the force of gravity. According to Newton’s law of universal gravitation, any two objects exert an attractive force on each other that is proportional to the product of their masses and inversely proportional to the square of the distance between them, expressed as:

$F = G \frac{m_{1} m_{2}}{r^{2}}$

In the experiment, Henry Cavendish used a torsion balance to measure this incredibly faint gravitational pull. He suspended a rod with two small lead spheres from a thin wire and placed two larger lead spheres nearby. The gravitational attraction between the large and small spheres caused the rod to rotate, twisting the wire. By measuring the displacement of the rod against the wire's restoring force, Cavendish was able to calculate the magnitude of the gravitational force between the masses.1