The Growth and Decay of Photo-thermionic Currents from Oxide-coated Filaments. H. D. ARNOLD and H. E. IrEs. (Proc. Nat. Acad. Sciences, Dec., I92L)--Merritt and Case have shown that the illumination of the oxide-coated filament of an audion is followed by an increase of the current between the filament and the plate. Merritt further showed that the increase was chiefly due to radiation of short wave-length and interpreted the effect as due to an increased emission of electrons from the filament under the excitation of the incident light.
In the present investigation light that had passed through a red glass fell on the filament. The change in space current was recorded by a string galvanometer. It was concluded that the heating effect of the red light is mainly responsible for the changes occurring. When light transmitted by blue glass was used the heating effect was quite small, yet there was still a change in the space current. A study of this, as the heating current in the filament varied, led the authors to believe that some light effect different from the true photo-electric effect is the cause of the phenomenon. There is a similarity in the features of the growth and decay of the current to the variation of selenium in resistance under illumination that justifies the suggestion " that the cause of the light effect in the oxide-coated filament may be closely related to that which gives selenium its photo-sensitive properties." G. F. S.