After 1922, experimental interest increased, particularly in the groups led by Millikan at the California Institute of Technology (Caltech) in Pasadena, California, and by Gossling at the General Electric Company in London. Attempts to understand autoelectronic emission included plotting experimental current–voltage (i–V) data in different ways, to look for a straight-line relationship. Current increased with voltage more rapidly than linearly, but plots of type log(i) vs. V were not straight. Walter H. Schottky suggested in 1923 that the effect might be due to thermally induced emission over a field-reduced barrier. If so, then plots of log(i) vs. √ V should be straight, but they were not. Nor is Schottky's explanation compatible with the experimental observation of only very weak temperature dependence in CFE – a point initially overlooked.