Factors affecting the design of an automatic electron-trajectory tracer

The paper describes a new method of determining electron trajectories in an electrostatic field. Information derived from a model electrode system in an electrolytic tank is passed automatically and continuously to a differential analyser, where the equations of motion of the electron are integrated and its trajectory is traced on an output table. Electric-field components in the tank are sampled by means of pairs of probes dipping into the electrolyte, and the voltage between the two probes of each pair is balanced automatically on a potentiometer and is thus converted into a shaft rotation which can be fed into the differential analyser. The output shafts from the differential analyser determine the mean position of the probes in such a way that it moves along the trajectory which is being plotted. Results obtained with apparatus based on these principles are described, and a detailed analysis of the factors affecting the overall accuracy is included in the paper. The conclusion is reached that the method is a promising one, but that a digital computor would give much more satisfactory results than the differential analyser which was used.