Coulomb’s law, a simple mathematical statement,  was
initially experimentally arrived at  in the manner described
above While the original experiments established it at a
macroscopic scale, it has also been established down to
subatomic level  (r ~ 10–10 m) Coulomb discovered his law without knowing the explicit
magnitude of the charge In fact, it is the other way round:
Coulomb’s law can now be employed to furnish a definition
for a unit of charge