Both the amplitude and the phase of the ionospheric potential and Carnegie curve of atmospheric electricity are considered to distinguish causes for the negatively charged earth in fair weather. Satellite-observed longitudinal distributions of electrical activity are convolved with local diurnal variations of cloud-to-ground lightning and point discharge current to produce universal dirurnal variations which are compared with the Carnegie curve. The amplitude ratio (maximum-minimum)/mean) for the predicted universal diurnal variation of point discharge shows good agreement with the Carnegie curve, whereas the predicted amplitude ratio for lightning is 2--3 times greater. These comparisons suggest that conduction current other than lightning is the dominant charging agent for the Earth's surface. ¿American Geophysical Union 1993