In 1776, he
returned to Paris and
retired to a small estate
to do his scientific
research 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