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A study has been made of thermionic emission from tungsten filaments cataphoretically coated with alkaline earth oxides. It was found that the emission from the oxide‐coated filament was not influenced by the variation of work‐function with crystallographic direction of the base metal. A Richardson plot of emission at zero field yielded an apparent work function of 1.3 volts and an A value of 0.048 amp/cm2‐deg2. In retarding potential data, the energy of thermionic electrons showed an apparent deviation from Maxwell‐Boltzmann statistics. This deviation was interpreted as due to a potential drop through the coating. Such an interpretation led to a conductivity activation‐energy of 1.3 volts. A strip theory of patches was used to explain the accelerating potential data. Satisfactory agreement with experiment was found with a patch amplitude of 0.2 volt and a period of 2×10-6 meter.