CXX. A theory of the abnormal cathode fall

Summary A theory of the abnormal cathode fall is given, according to which conduction in the dark space is closely analogous to that in a high vacuum between a plane thermionic cathode and plane anode. According to the theory, the width of the dark space with given current and voltage should be determined by the atomic weight of the gas and universal constants. The theory is compared with the measurements of Aston and of Aston and Watson. The relatively small divergence between the simple theory and experiment can be removed, partially at least, by taking into account the electrons liberated at the cathode, information concerning which is given by Cheney's measurements, and the collisions of the positive ions with neutral molecules. But it seems difficult to reconcile the theory with Aston's determination of the variation of the electric field through the dark space.