Dependence of the transition from Townsend to glow discharge on secondary emission

In a recent paper Sijacic and Ebert have systematically studied the transition from Townsend to glow discharge, refering to older work from von Engel (1934) up to Raizer (1991), and they stated a strong dependendence on secondary emission gamma from the cathode. We here show that the earlier results of von Engel and Raizer on the small current expansion about the Townsend limit actually are the limit of small gamma of the new expression; and that for larger gamma the old and the new results vary by no more than a factor of 2. We discuss the gamma-dependence of the transition which is rather strong for short gaps