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On wireless interference phenomena between ground waves and waves deviated by the upper atmosphere.
536
CURRENT TOPICS.
[J. F. I.
On Wireless Interference Phenomena between Ground Waves and Waves Deviated by the Upper Atmosphere. E . V . APPLETON and M. A. F. BARNETT. (Proc. Royal Soc., A 7 6 4 . ) - - T h e experimental evidence for the existence of the Kennelly-Heaviside layer is accumulating. This is an ionized stratum of the atmosphere high above the earth from which electrical waves are reflected. The authors of this paper in a previous communication related how they determined the angle of incidence of electrical waves assumed to be reflected from the layer, and interpreted their results " as yielding a direct experimental proof of the existence of the Kennelly-Heaviside layer, and also as demonstrating that the ' f a d i n g ' of broadcasting signals at moderate distances from the transmitter was due mainly to interference phenomena between two sets of waves arriving at a receiver with an appreciable path difference." In the present paper they make use of another method published by them about two years ago. It is analogous to Lloyd's mirror interference system. Let light fall at almost grazing incidence on a horizontal mirror and after reflection proceed to a vertical screen, upon which is incident also light from the same source that arrives without having been reflected. The two rays falling on the screen have traversed different paths, and may, therefore, arrive in different phases. For one length of wave their effects will reinforce each other; for a different length they will be in opposition. Substitute for the source of light the sending station, for the mirror the layer in the upper air and for the screen the receiving station. In the experimental work a station near Peterborough received, while two sending stations were used at Bournemouth and at the National Physical Laboratory. The respective distances were 236 and I24 km. " Considerable difficulty has been experienced in finding a small wave-length range suitable for the experiment and free from interference by Continental broadcastmg stations, which often transmit to 2 or 3 A.M." The wave-lengths employed were from 36o to 4oo m. At the receiving station poorly selective amplifiers were made use of and photographic registration of the effect was obtained with an Einthoven galvanometer. A change of emitted wave-length was made uniformly during 5 secs., the change being 5 or Io metres. All the 4oo records taken show " the variation of the rectified signal current with time." Several reproductions of records are given. One pair was taken between the same stations and with the same original wave-length, but in one case the change was 5 m. and in the other twice as much. In the latter case the record shows twice as many maxima as does the former. The authors interpret their observations as showing that the equivalent height of the reflecting layer rises gradually during the night only to sink rapidly about half an hour before sunrise. The reflected ray disappears altogether as the morning proceeds. G. F. S.
CURRENT TOPICS.
[J. F. I.
On Wireless Interference Phenomena between Ground Waves and Waves Deviated by the Upper Atmosphere. E . V . APPLETON and M. A. F. BARNETT. (Proc. Royal Soc., A 7 6 4 . ) - - T h e experimental evidence for the existence of the Kennelly-Heaviside layer is accumulating. This is an ionized stratum of the atmosphere high above the earth from which electrical waves are reflected. The authors of this paper in a previous communication related how they determined the angle of incidence of electrical waves assumed to be reflected from the layer, and interpreted their results " as yielding a direct experimental proof of the existence of the Kennelly-Heaviside layer, and also as demonstrating that the ' f a d i n g ' of broadcasting signals at moderate distances from the transmitter was due mainly to interference phenomena between two sets of waves arriving at a receiver with an appreciable path difference." In the present paper they make use of another method published by them about two years ago. It is analogous to Lloyd's mirror interference system. Let light fall at almost grazing incidence on a horizontal mirror and after reflection proceed to a vertical screen, upon which is incident also light from the same source that arrives without having been reflected. The two rays falling on the screen have traversed different paths, and may, therefore, arrive in different phases. For one length of wave their effects will reinforce each other; for a different length they will be in opposition. Substitute for the source of light the sending station, for the mirror the layer in the upper air and for the screen the receiving station. In the experimental work a station near Peterborough received, while two sending stations were used at Bournemouth and at the National Physical Laboratory. The respective distances were 236 and I24 km. " Considerable difficulty has been experienced in finding a small wave-length range suitable for the experiment and free from interference by Continental broadcastmg stations, which often transmit to 2 or 3 A.M." The wave-lengths employed were from 36o to 4oo m. At the receiving station poorly selective amplifiers were made use of and photographic registration of the effect was obtained with an Einthoven galvanometer. A change of emitted wave-length was made uniformly during 5 secs., the change being 5 or Io metres. All the 4oo records taken show " the variation of the rectified signal current with time." Several reproductions of records are given. One pair was taken between the same stations and with the same original wave-length, but in one case the change was 5 m. and in the other twice as much. In the latter case the record shows twice as many maxima as does the former. The authors interpret their observations as showing that the equivalent height of the reflecting layer rises gradually during the night only to sink rapidly about half an hour before sunrise. The reflected ray disappears altogether as the morning proceeds. G. F. S.