The dielectric properties of some homogeneous materials at high electric stress

Specimen-electrode systems suitable for measurements at high stress are considered, and the stresses estimated for which they are suitable. Measurements at 50 c/s on mica, polystyrene and phenol formaldehyde up to stresses of the order of 106 V/cm, approximately equal to one-fifth of the intrinsic electric strengths, show that the changes of phase angle, if any, do not exceed 0.0005 With phenol formaldehyde an increase of capacitance of 2.5 parts in 1 000 was observed.