The permittivity and power factor of micas

Attention is drawn to the electrode difficulty in testing mica, and tests are described which show the order of contact effect which may be obtained with ordinary mercury electrodes. Means are described by which electrode contact effect with mica may be entirely eliminated, and test results are given proving this point. Finally, test results on the power factor and permittivity of ruby, green and amber micas are given, together with the variations produced by changes of stress and temperature. It is shown that over the range of samples tested, the properties of each grade lie within close limits, but that the properties are widely different for the different grades.