*
Implicit in this is the assumption of additivity of charges and conservation:
two charges (q/2 each) add up to make a total charge q Charles Augustin de
Coulomb (1736 – 1806)
Coulomb, a French
physicist, began his
career as a military
engineer in the West
Indies 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