IN a uniform field, Paschen's law, namely, breakdown voltage V = f(p.d) (where p is the gas pressure and d is the gap distance), holds for values of p up to about 10 atm., beyond which the improvement in electric strength of air becomes progressively less than would be expected from this relationship. Most published data extend only up to some 1,200 lb./in.2, and beyond this pressure information is sparse and predictions of the electric strength, E, are difficult as a result of the lack of experimental data. The cause of this departure from Paschen's law may be attributed to the nature of the electrode surfaces. At high pressures, the electric strength of air is dependent on the shape, disposition and material of the electrodes and also on the degree of smoothness of their surfaces1–3.