I believe that the reason that the ampere is chosen as the base
unit in the SI system is that it is a much easier unit to maintain
practically. Since the ampere can be defined in terms of the force
between two current carrying wires, it is possible to design very accurate
current balances that can be used to standardize the unit. The coulomb,
on the other hand, is defined in terms of an electrostatic experiment
leading to much greater difficulty in developing standards.
While all this might not be as esthetically pleasing as we would
like, we have to remember that having a standard for current that
facilitates easy comparisons has important commercial consequences.
Dr. Mark H. Shapiro
Physics Department
California State University, Fullerton
Fullerton, California 92634