A method is described for initiating a current discharge through an object, e.g. a spark-gap, which is initially broken down by a separate impulse-voltage generator. The isolation of the current source necessary to enable the impulse voltage to be developed across the object is provided by a chain of spark-gaps; these are arranged to break down subsequently, in succession, and so complete the discharge path for the current source. This arrangement offers a number of advantages over the microsecond switch due to Bellaschi.An analysis of the operation of the initiating circuit is given; this enables the number and settings of the auxiliary gaps to be determined when account is taken of the various factors that affect the electrode voltages. The causes and effects of incorrect operation are considered and means of inhibiting the discharge of the current source under these conditions are described.The method has been used in the production of current pulses for spark-discharge work, in a gap with a breakdown voltage of up to 150 kV. A delay of about 1.0 microsec between breakdown and the start of the current discharge has been obtained with an initiating circuit having five gaps.