410 AUSTIN— ENERGY IN RADIOTELEGRAPHY. [April 19, 



retically it is dififiicult to understand how this great difference in 

 antenna resistance can be produced without changing the field dis- 

 tribution so as to vary the capacity and wave-length, but what is 

 still more remarkable, is that it is found that the ratio between the 

 current in a receiving antenna a few miles distant and the sending 

 current at Arlington remains absolutely unchanged whether the 

 towers are grounded or insulated. But since the sending current 

 with the towers grounded is approximately 50 per cent, larger than 

 when the towers are insulated, they are always kept grounded. For 

 receiving at Arlington there is practically no difiference. 

 Referring again to the formula for the received current 



Ij,= 4.2S-jj^ he 



^/A 



it will be noticed that, if we disregard the absorption term, it bears 

 a striking resemblance to the Hertzian equation for the amplitude 

 of the electric force in the equatorial plane of an oscillator.'* This 

 equation in the form given by Zenneck is^' 



(2) £,= 2.T^-§'3-io'^^C.G.S. 



where £0 is the electric amplitude at the distance d, I the length of 

 the oscillator, and /q the current amplitude in the oscillator, and was 

 derived for continuous oscillations and for an oscillator consisting 

 of two large spheres connected by thin wires with a spark gap in the 

 middle ; an arrangement which produces a uniform current distri- 

 bution throughout the wires. If we substitute the effective values 

 of the electric field E and current / in the antennas, in place of the 

 amplitudes, the equation will, of course, remain true. Therefore, if 

 we are able to determine the length of the Hertzian oscillator which 

 will be equivalent to a wireless antenna, we have at once a very con- 

 venient means of calculating the electric field at any distance not 

 great enough to have the absorption come into play. Theoretical 



* This applies strictly only to values of d amounting to a large number 

 of wave-lengths. 



^J. Zenneck, " Lehrbuch der drahtlosen Telegraphic," p. 45. 



