Some of the properties of an electron emission system have been investigated by means of a special electron gun, for accelerating voltages in the range 18-30 volts. The voltage was varied in steps of 1 or 2 volt intervals, and it was found that the emission varied in a periodic manner over all regions of the cathode - marginal, extra-axial and central; the variations were greatest for the central region. Here, the change from `normal' to `abnormal' may occur over a one volt energy interval; an energy change of two volts can alter the periodic pattern and convert a maximum of emission density into a minimum. Changes of temperature of some 30°C also produce profound effects on the form of the distributions.
Anomalies also appear in the total current to the axial system of collectors. For example, for every beam energy between 21 and 23.8 volts, there are three separate temperatures of the emitter at which `threshold' current begins to flow.
The pattern of standing waves across the emitter has a wavelength of about 0.01 mm. This is interpreted as arising from the presence of a saddle-back field produced by initial velocity effects together with the space charge of the beam. The electrons oscillate in this field. An analogy is afforded by the occurrence of oscillations under certain field conditions for the transition region between lens and mirror in the case of the symmetrical arrangement of electrodes.