The behaviour of a low pressure intermittent gas discharge in air is studied at various values of pressure and as a function of the parameters of the external circuit. It is shown that the `self-capacity' of the discharge does not represent a true capacitive effect due to charged particles in the inter-electrode gap, but can be explained in terms of the finite width of the discharge pulse. Empirical relations connecting the critical potentials, the pulse width and the circuit capacity are presented.