Abstract:
Part I of this thesis is concerned with the measurement of the natural atmospheric electric field. In Chapter 1, two new field mills are described and discussed. The asymmetrical mill has specially shaped plates and generates a signal from which the sign (direction) as well as the magnitude of the field can be determined without the need for a synchronous detector and its associated phase reference generator. The effects of noise on the performance of the mill have been examined in some detail and the results, which have been confirmed experimentally, show that although simple, the asymmetrical mill has several undesirable features. The high frequency synchronised mill is more complicated electronically but does not have many of the undesirable features peculiar to the asymmetrical mill while retaining the advantage of giving sign discrimination without needing a separate mechanical arrangement to generate a phase reference signal for its synchronous detector. Chapter 2 considers the problem of calibrating field mills under plane screens and a method is developed which enables accurate calibrations to be performed even when the screen is relatively small.