Practical considerations in the reconciliation of the direct and indirect methods of measuring the air-earth current

Abstract

Progress in any field of scientific interest is often advanced by the failure to find agreement between two different approaches to a particular measurement in the field. This is so because it forces attention on the theory behind the measurements and the conditions under which the measurements were made. Such a problem is identified in the field of Atmospheric Electricity. Differing results have been found for the value of the fine weather air- earth current when measured by the "indirect- and "direct'' methods of approach. The indirect method involves the recording of the fine weather conductivity and the potential gradient and equating their product with the conduction current. In the direct method, the total charge arriving at a portion of the earth's surface is measured. The direct method, though more difficult, appears to be the more fundamental measurement and a critical review of previous experiments and the hypotheses attempting to explain their differing results, is made. The limitations of work at ground level, in that it predicts a system from the examination cf one of the system's boundaries, is indicated. The experimental problems associated with the direct and indirect methods are described with particular reference to the site used for the measurement of atmospheric electricity at Durham Observatory. In particular, the effects of pollution and the displacement current are discussed and some details of an unsuccessful attempt to devise a form of the direct method that would enable the true magnitude of any convection current to be found, are given. Suggestions are made for the measurements required and the conditions under which they should bo made if the final resolution of those differences in the recording of the fine weather air-earth current is to be achieved.