A description is given of an electronic sequence control circuit for the operation of a Wilson cloud chamber used in cosmic‐ray work. Necessary delays are introduced by unbalanced multivibrator circuits whose periods are adjustable by means of potentiometers. The circuit operating the magnetic‐type valve makes use of two thyratrons, one to conduct the valve current and the second, to interrupt it, permitting large values of this valve current and therefore fast action. Minor modifications readily adapt the circuit to a chamber used in other investigations.