Abstract
The increase in electron path length, particularly at low electron energies, evaluated on the basis of the formula given by Massey and Burhop, and the consequent increase in the ionization cross section measurements reported by Tate and Smith are not born out by the recent experiments. It is shown that the size of the electron path length is not governed by the diameter of the final aperture alone but primarily by the energy available to the electrons normal to the field direction. This analysis shows that, in agreement with experimental observations, there is negligible increase in electron path length in the Tate and Smith experiments.