Measurements in electrical engineering by means of cathode rays

This paper is intended as a survey of the present state of knowledge on the subject of the use of cathode rays for measurement purposes in electrical engineering, and specially with a view to possible future developments. Part 1 introduces the subject of measurement methods. Section (I) describes various ways in which information on physical quantities may be obtained by applying them to suitably devised instruments, and in Section (II) is given the history of the development of such instruments, with special reference to those for studying variable quantities. In Section (III) are described various means of producing cathode rays and how they came to be applied to measuring instruments. Part 2 deals in greater detail with measuring apparatus using cathode rays (i.e. an "electron jet") as a "pointer." Sections (IV) and (V) describe historically the development of such apparatus by successive workers in the field, with brief references to the purposes for which it was devised. Certain special problems arise in the use of such apparatus for accurate measurement, and Sections (VI) and (VII) indicate how the solution of these problems has been tackled. In Section (VIII) the auxiliary apparatus found necessary for the study of variable quantities is described. Part 3 contains a brief resume of some of the limitations of the methods described in the paper, and indicates some possible lines of future development. In an Appendix is given an investigation (partly mathematical and partly historical) of certain essential properties of the electron jet as used in the instruments described.