RADIOTELEGRAPH Y—-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 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. 
Sea 
. 
Zz re 
sin DAYTIME OVER os ” 
“THWHOLE ATLANTIC & mu = 
WHOLE ATLANTIC 
OURING VHICH SIGNALS 
ARE VERY VARIABLE yy" 
IM STRENGTH VARYING 
> FROM VERY WEAR To 
VERY STRONG , STORNSE 
= NIGHT OVER 
u 
« 
td 
< 
wu 
2 
4 
z 
> 
GLACE GAY 
SUNRISE av 
GL 
\ CLIFDEN 
—_—— _—_—_—o 
ANO MGONLICHT MAY it 
AVE f AN INFQUENEES rg 
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. 
