[en] The cross section and the current density at the two ends of a positive column, measured as functions of pressure, were found to be different in glow discharges operated between copper electrodes in air, nitrogen and helium in the pressure range of 100-760 Torr and at an electrode distance of 7 mm. Taking into consideration the occurrence of the dissociative recombination of positive molecular ions, the observed difference is explained by the different pressure dependences and magnitudes of the cathode and anode falls, which determine the current densities at these places. (author)