RADIOTELEGKAPHY MARCONI. 



125 



cate with these shore stations unless by means of specially powerful 

 instruments. 



It is also to be noticed that in order to reach ships in the Mediter- 

 ranean 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 the daytime. Although no such obstacles lie between the 

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

 for North America, a night transmission of 1,000 miles is there of 

 exceptionally rare occurrence. The same effect3 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. 



S»«.t _ « 5 NIGHT OVER Z 2 



wui WHOLC ATLANTIC Jq 



Z ct OURiNC WHICH 5ICNRIS o — 

 v3 ^ ARE VERT VARIABLE ,Jf> jj 

 VtRYJ 3jJ .NSTRENC.TH VARYING. % yt} 



' J 8 :■! S» STROWC - 5T0Rn5li i 



5,tN«i DAYTIME OVER "£ 



w VHOlEflTLflNTICs2 

 §3 





VtRY STRONC, . 5TORt1 

 ~HAVC M OCCIOEOEr 

 ANO MOONIICHT T\K 

 ■JAVE AN INFLUENCE 



' T'?*r 



CVREENWKjWTWH 



Fig. 8. 



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 a 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. 



I have here some diagrams which have been carefully prepared 

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

 signals received at Clifden from Glace Bay. 



The curves traced on the diagram (fig. 8) show the usual varia- 

 tion in the strength of these transatlantic signals on two wave lengths 

 — one of 7,000 meters and the other of 5,000 meters. 



