The control of current across a spark gap by means of an external magnetic field

An experimental study was made of the electrical discharge between parallel plates when the pressure between the plates had been reduced to a value slightly less than the critical pressure—i.e. to the condition when a tube begins to harden. Under these conditions the application of a transverse magnetic field will produce a discharge between the electrodes for potentials less than the normal potential required. It is believed that this is due to the lengthening of the path traversed by the ions in crossing the gap. The results obtained may be harmonized by means of the values found by Carr (Proc. Roy. Soc. 1903) who made a study of Paschen's Law in the region of critical pressure. In general it is found possible, under the conditions studied, to start a discharge and control the value of the current through a circuit of which the gap is a part by means of varying the magnetic field superposed on the gap and without altering either the impressed E.M.F. or the ohmic resistance of the circuit.This control is effected by altering the effective length of the spark gap in the circuit by means of the external magnetic field.