He invented a
torsion 
balance 
to
measure the quantity of
a force and used it for
determination of forces
of electric attraction or
repulsion between small
charged spheres He
thus arrived in 1785 at
the inverse square law
relation, now known as
Coulomb’s law The law
had been anticipated by
Priestley and also by
Cavendish 
earlier,
though 
Cavendish
never published his
results Coulomb also
found 
the 
inverse
square law of force
between unlike and like
magnetic poles