Discussion on “effect of altitude on the spark-over voltages of bushings, leads and insulators,” (Peek) and “insulator depreciation and effect on operation” (Austin), New York, December 11, 1914. (see proceedings for December,

Harvey L. Curtis: For many years it has been known that there may be considerable leakage over the surface of insulators. However, it is only within a comparatively short time that quantitative measurements have been made. The present investigation^∗ was undertaken to determine the conditions under which leakage would become troublesome in the use of electrical instruments. It has been extended to cover a considerable number of insulators; and for these the effects of temperature, humidity, voltage and exposure to light were studied.