 In common gas-filled tubes, such as those used as gaseous ionisation detectors, magnitudes of currents flowing during this process can range from about 10−18 amperes to about 10−5 amperes.Townsend's early experimental apparatus consisted of planar parallel plates forming two sides of a chamber filled with a gas.A direct current high-voltage source was connected between the plates; the lower voltage plate being the cathode while the other was the anode.