. But otherwise, the result depends upon the path of the displacement.
FIG.4.
In this case, therefore, a vector suffers a change,
(in its direction, not its magnitude), when it is carried from a point
of a closed curve, along the curve, and back to P. We shall now calculate this vector change:
As in Stokes' theorem for the line integral of a vector around a closed curve, this problem may be reduced to the integration around a closed curve with infinitely small linear dimensions; we shall limit ourselves to this case.