Discussion on “the reluctance of some irregular magnetic fields” (Douglas), Deer Park, Md., June 29, 1915. (see proceedings for May, 1915)

Charles R. Underhill: I wish to call attention to a special case of reluctance. It has to do with solenoid design; the design of plunger electromagnets, or magnets with movable cores. Let it be assumed that a constant mean effective alternating e. m. f. at constant frequency is to be impressed upon a coil. When the constant mean effective alternating e. m. f. is impressed upon the coil, it is found that a certain mean effective current flows through the coil, and from this knowledge together with the number of turns and the dimensions of the coil, the permeance of the coil can be calculated, and since reluctance is the reciprocal of permeance it is a simple matter to determine the reluctance of the coil.