The stable corona discharge has found use in a large number of electrostaticapplications and one of their important properties is the inception voltage which can beeasily and accurately measured. The empirical Peek's law which yields the corona inceptionfield is previously made in standard air for wire-to-cylinder geometry and used for manyyears. However, the generalisation of this law, which at present derives from Hartmann'sphysical-mathematical model, requires new measurements with varying air physical parameters.This classical law expresses the inception field at the anode surface in function of theanode diameter, the related air density and the humidity. New measurement method ofthepositive DC corona-current voltage characteristics have been introduced in a wire-to-cylinderand wire-to-plane systems. Remarkable similarities between these basically different systemsare shown in this paper and the steady corona-current voltage characteristics are describedby the Townsend's square law in a large range of related air density. The normalizationfactor at air density equals unity and the humidity function suggested by the model are also determined from the measurements. The model values of the inception field at the wire surfaceagree with measured values in both wire-to-cylinder and wire-to-plane systems.