The apparent (measured) electric strength of a liquid dielectric depends on the nature of the cathode used. The field emission of electrons from the metallic cathode is assumed to be responsible for this effect; it may provide space charge which distorts the electric field in the dielectric. The nature of the cathode determines the range of electric fields over which the emission becomes appreciable. In this paper we discuss in detail the emission of charge and the formation of space charge. Because of theoretical and experimental uncertainties connected with supposedly uniform metallic surfaces, an electrode consisting of an electrolyte solution is also considered. Although the experimental results demonstrate that ions are emitted from such cathodes under the influence of strong electric fields, the role in providing space charge is similar to that of metal electrodes which emit electrons. For the former electrode, the considerations regarding space‐charge formation predict a definite dependence of apparent electric strength on electrolyte concentration and provide a way of testing the basis of the theory. Certain experiments reported here confirm the predictions of the theory.