Re-Focussing of Electron Paths in a Radial Electrostatic Field

Abstract

The method which utilises a uniform magnetic field is the one customarily employed for the analysis of electronic velocities. As the presence of a magnetic field is objectionable in certain investigations, analysis by an electrostatic field was considered. The theoretical considerations for a two-dimensional, inverse first power, radial electrostatic field (given in the preceding paper) show re-focussing at 127\ifmmode^\circ\else\textdegree\fi{}17\ensuremath{'} of the same order as that in the magnetic case at 180\ifmmode^\circ\else\textdegree\fi{}. The present paper describes the apparatus and procedure used in verifying the predicted re-focussing at 127\ifmmode^\circ\else\textdegree\fi{}17\ensuremath{'}. A radial electrostatic field was produced by a difference of potential between two coaxial cylindrical surfaces. Three oxide coated filaments allowed electrons to enter the field either normally or in directions making 5\ifmmode^\circ\else\textdegree\fi{} with the normal. Satisfactory refocussing and resolution were found.