Consider n charges on the horizontal axis, with their coordinates xk and their charges qk. The equation of the lines of force is similar to (1):
This equation can be deduced delimiting a "tube of force"
by revolving a portion of a line of force around the horizontal axis. Obviously
there is no flux through the "walls" of the tube. Then equation
(1') is really conservation of flux through any vertical section of the
"tube": flux is proportional to solid angle for point charges,
and the solid angle through a transverse section is 
.
Thus the methods designed above to study lines of force and equipotentials created by two charges can be applied to this situation as well.