LONDON, EDINBURGH, and DUBLIN 



PHILOSOPHICAL MAGAZINE 



AND 



JOURNAL OF SCIENCE. 



[SIXTH SERIES.] 



DECEMBER 1907. 



LXVTIL On Magnetic Oscillators as Radiators in Wireless 

 Telegraphy. By J. A. Fleming, D.Sc, F.R.S.* 



AN oscillator of the open or Hertzian type is commonly 

 called an electric oscillator because the effects produced 

 in the external field are to a large extent determined by 

 the potential o£ the free electric charges which alternately 

 make their appearance on the open ends. If, however, the 

 oscillator consists of a metallic circuit completed by a con- 

 denser, the plates of which are very near together, the effects 

 in the external space are mostly or entirely determined by 

 the current in the circuit and little if at all by the con- 

 denser-plate charges, because these being of opposite sign 

 and near together neutralize each other's effects in the field. 

 Such a closed or nearly closed circuit is called a magnetic 

 oscillator. In the case of an open oscillator or simple doublet 

 Hertz showed that if (j> is the maximum electric moment, or 

 product of the maximum static charge on each end and the 

 distance between them, and if X is the wave-length of the 

 emitted radiation, the energy radiated by the oscillations in 

 ergs per period is given by the expression 



*=w « 



This expression can be reduced to a more convenient form 

 for practical measurement as follows : — 



Let C be the capacity in microfarads of each sphere or 



* Communicated by the Physical Society : read October 25th, 1907. 

 Phil. Mag. S. 6. Vol. 14. No. 84. Dec. 1907, 2 Z 



