Abstract :
Many measurements are recorded of the strength at Cambridge of the signals from Horsea during September 1921, in which the Vallauri method of measurement was employed. The field strength is deduced from the measured E.M.F. of the signal, the effective height of the receiving aerial being determined experimentally both from the distribution of current in the aerial up-lead, and by comparing the receptive power of the aerial with that of a loop. Incidentally, the measurements of effective height provide a very accurate verification of the law that for short distances the E.M.F. set up in an aerial is in direct proportion to the frequency of the incident waves. It is found that at a wave-length of 3 000 m the Horsea signals suffer in their journey an absorption of 40 per cent, and evidence is produced of a regular diurnal variation of intensity. The accuracy of the aural method of comparison is discussed, and the feasibility of making long-distance measurements with a visual indicator, instead of by aural comparison, is pointed out
