From the known approximate solutions of the problem of ship wave resistance we may, with the degree of accuracy of these solutions, investigate the influence of a change of ship form upon the wave resistance. The problem not being linear, it is of course, having regard to the mutual induction between the different parts of the ship’s surface, not possible to indicate the influence of a finite change at one point as independent of that at another point. But for infinitesimal changes the problem may be considered as linear and in this case the solution can be given in a form very suitable for use in designing practice, viz., by constructing “influence lines” as sections of “influence surfaces” indicating the change in wave resistance for unit change of displacement at the different points of the surface of the hull. These curves show immediately at what points a given form should be modified in order to reduce the wave resistance and allow an estimate of the tendency and magnitude of the variation of the latter for a projected change of form.