The Electrical State of the Upper Atmosphere

Abstract

Preceding speakers having marshalled the available evidence for the Heaviside layer, it may be most useful for me, while agreeing broadly with the conclusions drawn from that evidence, to refer to some other points of view and other agencies. For example, in connexion with wireless phenomena at short distances from the transmitting station, the diminution of the density of the air with increase of height, which causes the lower atmosphere to act as a prism with its base on the ground, taken together with diffraction, must be remembered. Consider a source from which electric waves of length 20 metres, 600 metres, and 20,000 metres are being simultaneously emitted, and consider especially the rays emitted horizontally. Up to distances of 100 kilometres, all these waves can be detected by an ordinary aerial—beyond that distance the 20-metre waves vanish but the others remain perceptible. This, I suggest, indicates diffraction of the longer waves, as is supported by the fact that an aerial on a high mast or hill can detect short waves passing overhead like the beam of a searchlight. I want to suggest also that variations of signal strength at these short distances may be due to variations in or movements of the lower atmosphere. (The well-known vertical oscillations of pilot balloons at a height of 10 kilometres suggest movements of the air.)