Quantity is determined electro-statically by the repulsion a charge of
given quantity exercises upon an identical charge at a known distance.
The force evidently varies with the product of the two quantities, and
by the law of radiant forces also inversely with the square of the
distance. The dimensions given by these considerations is Q * Q/(L*L).
This is the force of repulsion. The dimensions of a force are
(M * L) /(T^2). Equating these two expressions we have:
(Q^2)/(L^2) = (M*L)/(T^2)
or
Q = ((M^.5)*(L^1.5)) / T
which are the dimensions of electrostatic quantity.