RADIOTELEGRAPH Y—FLEMING. 165 
all lower amplitudes that particular receiving arrangement is per- 
fectly deaf. Now, it is a matter of common experience that with a 
given radiotelegraphic apparatus and antenna, it is possible to re- 
ceive signals for greater distances over sea water than over dry land, 
and that if the soil is very dry the distance may be cut down very 
considerably indeed. This is not due merely to the difficulty of mak- 
ing what the telegraphists call a good earth at the sending station, 
it is due to the absorption of the wave by the earth for the whole 
distance which extends between the two stations. Hence, also, it is 
a common experience that when particularly dry weather is suc- 
ceeded by wet weather, the radiotelegraphic communication between 
two stations on land is considerably improved. 
In another paper Doctor Hack has shown that even underground 
water is an advantage in facilitating radiotelegraphic communica- 
tion. Since a shore station must always be established on shore for 
’ 
ws 
re 
re 
ne 1 1/10 
8S 
an 2 1/100 
SS 
os By distanc} 
SE 3 ance alone 1/1000 
aS 
ae 4 1/10000 
ae 
ay 
PS 5 1/10° 
£8 
SEs 
is) 
6 
; Kilometres 500 1000 1500 2000 3500 
Distance | wiles 312 625 937 1250 1562 
Fic. 5.—Curves showing decrease in wave amplitude with distance for 
waves 1,000 feet in length (Doctor Zenneck). 
communication with ships, it is in consequence generally the custom 
to select a site for that station as near as possible to the coast, and to 
take pains to get a very good conducting connection between the foot 
of the antenna and the soil, and also if necessary between the antenna 
earthplate and the sea. Fessenden has suggested for this purpose the 
use of what he calls a wave chute, which is merely a metallic network 
extending some distance outward from the antenna in cases where 
this antenna is established in the center of towns or dry districts. 
Doctor Zenneck has also given a series of curves which show in a 
remarkable manner the reduction in wave amplitude due to both dis- 
tance and surface absorption, calculated for waves of 1,000 feet in 
length, and for various coefficients of absorption (see fig. 5). Thus, 
for example, if we are propagating plane waves 1,000 feet long over 
a surface which by itself would reduce the wave amplitude to 0.867 
of its initial amplitude in 1,000 kilometers, then, when we consider 
the decrease by distance as well, we have to take account of the fact 
that this last cause reduces the wave amplitude at 1,000 kilometers to 
