The object of this paper is to point out an electrical experimental method for finding the torsional-stress distribution in cylindrical shafts of circular cross-section and of any axial outline. The method has been applied to the problem considered by F. A. Willers, and the paper includes a series of curves that will enable the designer to find, at a glance, the maximum torsional stress in a shaft of two diameters for various diameter and fillet proportions. It should be remarked that the results for a shaft of two diameters may be applied to most shafts of several diameters since the length of any two adjacent portions of the shaft are usually sufficiently long to make the analysis apply. Special shaft outlines, for instance shafts with oil throwers, can be investigated by the method.