AUSTIN: WIRELESS TELEGRAPHY NOTES 



101 



During the experiments in long distance radiotelegraphy 1 

 carried on at Brant Rock during the summer of 1910, the signals 

 sent out by the Birmingham lying at Newport were measured 

 at Brant Rock 45 miles away. The wave lengths used were 1000 

 meters and 3750 meters and the received signals were measured 

 on a 15 ohm tellurium-constantan thermoelement. 2 One milli- 

 meter on the thermoelement galvanometer corresponded to a 

 current of 263 X 10~ 6 amperes. 



The data of the observations are shown in the table. Under 

 the column Calculated, are given the values taken from Table 

 XVI of the paper cited. The difference between the calculated 

 and observed values represents the excess of the ground absorp- 

 tion over that which would have been observed if the waves had 

 passed over salt water. 



Birmingham at Newport, Received at Brant Rock 



If we consider the strength of signal which is proportional to 

 f , it will be found that 95 per cent of the energy was absorbed 

 in the case of the 1000 meter wave, while in the case of the 3750 

 meter wave the ground absorption was not detectable, the ob- 

 served signals being slightly stronger than the calculated values. 



The experiment explains fully why with the short wave lengths 

 ordinarily used, wireless communication has been so difficult 

 over this region and indicates that where such difficulties are 

 encountered longer wave lengths should probably be employed. 



i Bureau of Standards Bulletin, 7: 315. 1911. Abstract, this Journal, 1: 



1911. 

 2 See paper cited, p. 317. 



