As soon as an adequate charge system has been adopted, the potentials and
the field strength within the space can be computed. Whereas the potentials are
found by superposition, i.e. by eqn (4.71) or the corresponding set of linear
equations (compare with eqn (4.72)), the field stresses are calculated by superposition
of magnitudes and directional components. For a Cartesian coordinate
system, for instance, the x-coordinate Ex would then be for a number of n
charges.