How did Coulomb, who did not have a method for measuring charges, manage to establish the dependence of the modulus

How did Coulomb, who did not have a method for measuring charges, manage to establish the dependence of the modulus of the force of electrostatic interaction of bodies on their charges?

For reasons of symmetry, the pendant suggested that when two identical conducting balls come into contact, their total charge is equally distributed between the balls.

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