On the diurnal variations of the electric waves occurring in nature, and on the propagation of electric waves round the bend of the earth

Abstract

Since the earliest days of electric wave telegraphy it has been known that there exist natural electric waves which frequently affect the receiving apparatus at a wireless telegraph station more powerfully than do the message-bearing waves. In the telephonic method of receiving signals, where the apparatus is so arranged that the effect of a train of waves is to cause a pulse of electric current to pass from the “detector” through the telephones, the natural electric waves make themselves evident as clicks, or as rattling noises, in the telephones. They are easily distinguished from signals, for the sounds produced by the latter are more regular, and, in fact, are often musical in character. The natural electric waves are doubtless due to electric discharges taking place between masses of electrified air, or between such masses and the earth. Till recently it was not known whether the discharges affecting any particular station were taking place at distances of hundreds of miles or at distances of thousands of miles from the station; but it is now certain that for stations in England the distances concerned must usually be reckoned in thousands of miles. This point was settled by tracing and identifying individual natural wave trains at two receiving stations, one in London and the other in Newcastle. It was found that about 70 per cent, of the natural wave trains perceived at one station could be identified with those perceived at the other, and, further, that more than half of these were of much the same intensity at both stations— from which it may fairly be inferred that the distance of the discharge is great compared with the distance between the stations. The number of natural wave trains, or “strays” as they are commonly called for brevity, received at any station varies in general from hour to hour. In England these variations are most pronounced during the summer months, principally on account of the frequency of local lightning storms during these months. (The word local is here intended to mean within a radius of two or three hundred miles of the receiving station.) During the winter months, on the contrary, the number and intensity of the strays are relatively regular. The study of the phenomena belonging to the strays of distant origin may clearly be more favourably pursued in the winter than in summer, since the confusing feature of local lightning discharge is absent in winter. Besides the seasonal variations in the number and the intensity of the strays there is at every station a well-marked diurnal variation. Leaving out the irregularities due to local storms, we may say that the strays are in general more frequent and numerous during the night hours than during the day hours. The variations may be represented graphically as a curve in any of the methods indicated below and then they appear as shown in fig. 1, which may be regarded as a typical 24 hours’ continuous record of the integral of number and intensity. These diurnal variations have not yet been investigated thoroughly. The author has I not been able to find any account of observations in which the effects of local storms have been eliminated.