The geometrical aberrations of general electron optical systems I The conditions imposed by symmetry

During the past few decades, a great deal of information has been collected about the nature and magnitude of the image-forming and image-marring properties of optical and electron optical systems, the symmetry of which differs either slightly or radically from that of the familiar axially symmetrical systems. The present memoir opens with a brief survey of this work; in the subsequent sections, Hamilton’s point characteristic function and Sturrock’s work on perturbation characteristic functions are used to demonstrate the underlying unity behind all these scattered analyses, and to derive the properties of the imagery of any type of system.