Further measurements on wireless waves received from the upper atmosphere

In previous papers the authors have described the development of experimental methods of measuring the directions and relative intensities of both the electric and magnetic forces in wireless waves received at the earth’s surface from a distant transmitting station. In this work it was seen that the detection of the arrival of waves deflected from the upper atmosphere, and polarised with their electric force in a horizontal plane, was rendered difficult owing to the relatively great reflecting powTer of the earth resulting from its high conductivity. By a suitable choice of wave-length and careful attention to detail in the design and construction of the apparatus, however, the methods employed enabled measurements to be made on both vertically and horizontally polarised waves. The results of such measurements enabled a direct proof to be given of the fact that the fading of wireless signals on a vertical aerial and the variations of bearings experienced on the closed-loop type of wireless direction-finder are due to the reception respectively of vertically and horizontally polarised waves deflected from the upper atmosphere in their passage from the transmitter to the receiver. On arrival at the receiver, these indirect or atmospheric waves interfere with the direct or ground waves, in a manner determined by their relative magnitude and phase, and produce the intensity and apparent direc­tional variations mentioned above. The results of such interference phenomena have been investigated experimentally by Appleton and Barnett and by Holling-worth. In a more recent publication the present authors have provided experimental evidence showing that the path of the indirect waves is confined to the great circle plane between the transmitter and receiver. The measurements of the quantities in the received waves as previously described by the authors were confined to observations on the transmissions from the Bournemouth broadcasting station over a short period. The object of the present paper is to describe the continuation of these measurements and their extension to the transmissions from other stations.