Discussion on “control of direct-current hoists in iron and steel mills” (Stoltz and Lum), and “direct-current control for hoisting equipment in industrial plants” (Snyder), Pittsburgh, Pa., April 16, 1915. (see proceedings for

H. D. James: The paper by Messrs. Stoltz and Lum brings out the importance of continuity of service. The theoretical calculations in connection with the arcing of electric switches are difficult owing to the many factors that enter into the problem, yet it is the most important item that has to do with the maintenance of an electric contactor. The mechanical construction of a switch is easily analyzed and passed upon by a good mechanical engineer. The question, however, of the life of contacts, freedom from freezing and wear on arc shields and surrounding parts of the switch is still somewhat obscure. So many data on this question are of doubtful value because some of the factors are not available and others are not accurately determined.