The Propagation of Radio Waves over the Earth

Abstract

IN NATURE of March 7 there are two letters dealing with the subject of the transmission of electric waves over the earth's surface. Prof. Appleton has given some results which indicate that very marked interference effects occur at night. So far as I understand, he has suggested an interpretation of the experimental results in terms of the simple theory in which the maxima and minima of received intensity are supposed due to the interference of a direct ray over the surface of the earth, and a single reflected ray, passing from the earth to the Heaviside layer and back to the receiver. But the problem is scarcely so simple as this, for the multiple reflection may occur, the ray passing many times between the earth and upper layer before reaching the receiver. Such an effect would obscure the main results if the intensity of these rays were of the same order as those of the direct ray.