. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 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 shor
. Annual report of the Board of Regents of the Smithsonian Institution. Smithsonian Institution; Smithsonian Institution. Archives; Discoveries in science. 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 . VARYING. % yt} ' J 8 :?! S» STROWC - 5T0Rn5li i 5,tN«i DAYTIME OVER "£ wVHOlEflTLflNTICs2 §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, howeve
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