JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. I, DECEMBER 19, 1911. No. 10. 



RADIO-TELEGRAPHY. — A ship's antenna as a Hertzian oscil- 

 lator. L. W. Austin, Naval Wireless Telegraphic Laboratory. 



In the work on long distance radio-telegraphy 1 it was shown 

 that the equation giving the value of the current in the receiving 

 antenna in terms of the sending antenna current, the antenna 

 heights, the wave length, and the distance was identical in form 

 with the Hertzian equation for the amplitude of the electric waves 

 at a distance from the oscillator, provided this distance was not 

 great enough to involve the atmospheric absorption. 



I have made a calculation of the current which might be ex- 

 pected in a receiving antenna, making use of the form of radiation 

 formula given by Zenneck. 2 



# = 2 7r --3.10 10 c.g.s. 

 X d 



Here I represents the length of the oscillator, X the wave length, 

 J the current and d the distance in the equatorial plane from the 

 oscillator. The difficulty in applying the equation to the case 

 of the scout cruisers Birmingham and Salem lies in the determi- 

 nation of the dimensions of the electrical oscillator which would 

 be equivalent to the antenna system of the ships. Considering 

 the antenna as forming half the oscillator, the lower half of which 

 may be imagined to be below the surface of the sea, I would be 

 equal to 2/i where h is the height to the center of capacity of the 

 antenna. But, since the lower half of the antenna contributes 



1 Bull. Bur. Standards, 7: 315. 1911. 



2 Zenneck, Leitfaden der Drahtlosen Telegraphie, p. 43. 



275 



