1909] 



on Researches in Radiotelegraphy . 



659 



in radiotelegraphy. Every receiving apparatus associated with an 

 antenna of a certain height and kind must be subjected to waves of 

 a certain minimum amplitude to give any appreciable signal. For all 

 lower amplitudes that particular receiving arrangement is perfectly 

 deaf. Now it is a matter of common experience that with a given 

 radiotelegraph ic apparatus and antenna, it is possible to receive 

 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 

 making 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 

 succeeded by wet weather, the radiotelegraphic communication be- 

 tween two stations on land is considerably improved. 



^S 4 

 g'e 5 



73 -S 



1/10 



1/100 



1/1000 



1/10000 



1/10^ 



n-„*^^„^ {Kilometres 500 

 Distance ] ^^ .^^^ 3^3 



1000 



1500 

 937 



2000 

 1250 



3500 

 1562 



Fig. 5. — Cukves showing Decrease in Wave Amplitude with Distance 

 FOR Waves 1000 Ft. in Length. (Dr. Zenneck.) 



In another paper Dr. Hack has shown that even underground 

 water is an advantage in facilitating radiotelegraphic communication. 

 Since a shore station must always be established on shore for com- 

 munication 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 veiT 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 outwards from the antenna in cases where 

 this antenna is established in the centre of towns or dry districts. 



Dr. 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 1000 feet in 

 length, and for various coefficients of absorption (see Fig. 5). Thus, 



