 He forced the cathode to emit electrons using the photoelectric effect by irradiating it with X-rays, and he found that the current flowing through the chamber depended on the electric field between the plates.However, this current showed an exponential increase as the plate gaps became small, leading to the conclusion that the gas ions were multiplying as they moved between the plates due to the high electric field.Townsend observed currents varying exponentially over ten or more orders of magnitude with a constant applied voltage when the distance between the plates was varied.