Abstract :
The fading of a single magneto-ionic component of a radio wave of frequency 2¿6 Mc/s reflected from the ionosphere at vertical incidence has been recorded at two receiving points separated by about 100 m. On several occasions it has been deduced from the records that the fading is not due to the regular drift of a constant ground-distribution of e.m.f. past the observing point, but that it corresponds to a ground distribution which is varying irregularly at all points. Records obtained under these circumstances have been analysed on the assumption that the fading is caused by the random movement of irregularities in the ionosphere according to the theory suggested by Ratcliffe.9 The results agree, to a first order, with the assumption that in the ionspheric reflecting region there are irregularities moving with velocities in the line of sight which are distributed in a Gaussian manner with r.m.s. value of approximately 2 to 3 m/sec. There is, however, a significant discrepancy between the records and the results of the simple theory, and possible ionospheric causes for this discrepancy are discussed. There is some experimental evidence to suggest that the irregularities responsible for the fading are situated below the point where waves of frequency 4 Mc/s are reflected from region E.
