328 AUSTIN: SIGNALS IN RADIOTELEGRAPHY 



percentage steps, and partly to the shortness of the wave trains 

 which would not permit the direct and deflected trains to overlap 

 for any considerable difference of path. 



These facts indicate that the greater strength of night signals 

 is probably due not to a decrease in absorption, but rather to 

 additional energy which reaches the receiving station by reflec- 

 tion. This explanation would involve the idea that at night the 

 vipper atmosphere becomes stratified in such a way that at some 

 given height differing at different times, there is a sufficiently 

 sudden change in conductivity to permit reflection. It is con- 

 ceivable that this stratification is broken up in the day time 

 either by vertical convection currents, or by the more or less 

 irregular ionization produced by the ultra violet rays or cathode 

 particles from the sun.'^ 



It is certain that the difference between night and day signals 

 is much less at long waves than at short, but the observations on 

 the Clifden signals (X about 7000 meters) at Brant Rock (2460 

 miles) and at Arlington (2840 miles) do not agree with the obser- 

 vations of Marconi at Glace Bay that the day signals are equal 

 to or better than those at night.* At Brant Rock during the 

 autumn and winter the received current from Clifden thru 25 

 ohms resistance was in general about 35.10"'' amp. in the day 

 time, rising at times to 55.10"" amp., while at night the current 

 frequently amounted to more than 100. lO"*' amp. In summer 

 the signals were always faint and much of the time inaudible in 

 the day time, varying probably between 7.10"" and 12. 10"'^ amp. 

 Night signals were much louder, no exact measurements being 

 made on them. The observations on Clifden at Arlington agree 

 qualitatively with the Brant Rock results. 



^ The difference in summer and winter day signals at great distances perhaps 

 indicates that reflection plays some part even in the day time. 



* It is conceivable that the directive receiving antenna at Glace Bay may have 

 an influence on the phenomenon. 



