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XVI. On the Propagation of Electromagnetic Wares round 

 the Earth. 



To the Editors of the Philosophical Magazine. 

 Gentlemen, — 



IN my paper under the aboA*e title which appeared in 

 the issue of the Phil. Mag. for Sept. 1919, p. 365, 

 I derived an expression [(15) page 377] for the current, 

 generated in a receiving antenna for wireless telegraphy, 

 as a function of the constants of a transmitting station and 

 of the angular distance between transmitter and receiver. 

 This theoretical formula is based on the assumption of a 

 perfectly insulating atmosphere (cr = 0, e=l), and^ as an 

 instance, it was compared with Dr. Austin's measurements 

 of the received current at Darien due to the waves sent out 

 by the Nauen station. Unfortunately in this application of 

 Dr. Austin's data to our formula (15), a numerical oversight 

 crept in which Dr. G. Vallauri (Livorno) was kind enough 

 to point out to me in a private letter. 



The correct value yielded by (15) for the received current 

 is I 2 =T9 . 10" 10 amp. instead of 0'6 . lO" 12 amp. The value 

 obtained experimentally was 1'3 . 10 ~ 6 amp., hence, in this 

 instance, the theoretical value for the received current is 

 about seven tJiousand times too small. 



If, as another instance, we apply (15) to Dr. Austin's 

 measurements of the Eilvese-Darien transmission, we find 

 the theoretical value for the received current to be twelve 

 tJiousand times too small. 



Hence, notwithstanding this numerical oversight, the con- 

 clusion arrived at in my paper, that, assuming the atmosphere 

 to be a perfect insulator (<r = Q, e = 1), one obtains values for the 

 wave-amplitude at a big distance from a transmitting station 

 in flagrant contrast with the experiments, remains valid. 



Yours faithfully, 

 Physical Laboratory, BALTH. VAN DEK PoL, jun. 



Teyler's Institute, 

 Haarlem (Holland). 

 12. 4. 20. 



