Non-conductor

—1. A substance which does not allow the pa age of electricity through it at all, or only in a very small | degree; an insulator or dielectric. Strictly speaking, there is no substance which will prevent the pa age of electricity. The substances named in the following list are more or le efficient in the order in which they are given, the best non-conductor being named first: dry air, gla , paraffin, ebonite, shellac, gutta perch a, resin, silk, wool, porcelain, oils. The most efficient non-conductors lose their virtue if their surface be moist, the electricity pa ing by the conducting power of the moisture. This circumstance also shows why it is nece ary to dry previously the bodies on which it is desired to develop electricity by friction. 2. Any material which is a poor conductor of heat. Such non-conductors are used as a covering for steam pipes or for retaining the cold in refrigerators, etc.