I'm trying to learn and understand how Coulomb found is formula. This is from Wikipedia:

> He used a torsion balance to study the repulsion and attraction forces of charged particles, and determined that the magnitude of the electric force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.

Now the question and I didn't found anything about it. How is charged and mesaure the balls?
It was before the was batteries (and before volta...) and even if we create electrostatic on the ball, it can be exact number.

**In other words:** How to do the torsion balance using only the knowledge and materils we had?