202 



Gommendatore G. Marconi 



[June 2, 



Mediterranean, the electric waves have to pass over a large portion of 

 Europe and, in many cases, over the Alps. Such long stretches of 

 land, especially when including very high mountains, constitute, as 

 is well known, an insurmountable barrier to the propagation of short 

 waves during day time. Although no such obstacles lie between the 

 English and Irisli stations and ships in the North Atlantic en route 

 for North America, a night transmission of 1000 miles is there of 

 exceptionally rare occurrence. The same effects generally are notice- 

 able when ships are communicating with stations situated on the 

 Atlantic coast of America. 



Although high-power stations are now used for communicating 

 across the Atlantic Ocean, and messages can be sent by day as well 

 as by night, there still exist periods of fairly regular daily occurrence 

 during which the strength of the received signals is at a minimum. 

 Thus in the morning and the evening, when, in consequence of the 

 difference in longitude, daylight or darkness extends only part of the 

 way across the ocean, the received signals are at their weakest. It 

 would almost appear as if electric waves, in passing from dark space 

 to illuminated space and vice versa, were reflected and refracted in 

 such manner as to be diverted from the normal path. 



Later results, however, seem to indicate that it is unlikely that 

 this difficulty would be experienced in telegraphing over equal dis- 

 tances north and south on about the same meridian, as, in this case, 

 the passage from daylight to darkness would occur more rapidly over 

 the whole distance between the two stations. 



S.W-C OflYTIME OVER ^^ 

 ^"^''""WHOLEflTLflNTIC Siu- 



NOOFT" 



NIIIHT OVER 

 WHOLE ATLANTIC 



OURIN<; WHICH %1CNAIS S — 

 s3 ^ «RC WERY VABIRBLt sJ' ^ 

 , , IN STUENCTH VARYINC; |. 



'yi raxSH-vitr-ryjzhr.io~ { - 



VtRY STRONC, . 5TORn5| 



HWt A OCCIOEO tFFECl 



AND HOONLICHT DAY 



AVt AN INTLUENCtr 



Jj^ (^REtNWlCHTItlt 



Fig. 8. 



I have here some diagrams which have been carefully prepared 

 by Mr. II. J. Round. These show the average daily variation of the 

 signals received at Clifdcn from Glace Bay. 



The curves traced on diagram Fig. 8 show the usual variation in 

 the strength of these transatlantic signals on two wave lengths — one 

 of 7000 metres and the other of 5000 metres. 



The strength of the received waves remains as a rule steady during 

 day-time. 



Shortly after sunset at Clifden they become gradually weaker, and 



