The physical nature of the electrical breakdown of solid dielectrics

WHILE the physical phenomena in connection with the electrical rupture of gaseous insulators have been thoroughly investigated by J. J. Thomson, J. Stark, J. Townsend, J. B. Whitehead, F. W. Peek, Jr., and many others, the nature of the breakdown in solid and liquid insulating materials has up till now remained in complete obscurity. According to the prevailing opinion the rupture takes place at the moment when the density of the electrical field exceeds a certain limit at any point in the insulator. This is called the electrical strength of the material and is based on a reasoning analogous to that which gave rise to the theory of mechanical resistance against a breakdown.