6S2 Dr. J. A. Fleming on Magnetic Oscillators 



Hence we have in this case for the power W radiated in ergs 

 per second, 



w 10-4x156x177000 



^ = 551523 = ° 22 ( nearl - y) 



or about 52 microwatts. 



This is the energy sent out per second through the surface 

 o£ a sphere described round the oscillator the radius of 

 which is large compared with the wave-length of the oscil- 

 lator in question. 



It is evident therefore that the true radiative power of a 

 closed circuit of the above dimensions is extremely small 

 compared with that of an open oscillator of the same order 

 of linear dimensions. 



Hence when a closed circuit traversed by a high frequency 

 current acts to produce secondary currents in another similar 

 circuit at less than a wave-length distance from it, the chief 

 part of the effect cannot be due to true radiation or detached 

 energy but is the result of ordinary electromagnetic induc- 

 tion, or the creation of secondary currents produced by the 

 ebb and flow or pulsation of the lines of magnetic force per- 

 manently connected with the primary circuit*. 



Nevertheless experiment shows that such circuits may act 

 appreciably upon one another at very considerable distances, 

 when the primary circuit of one is traversed by a high 

 frequency current, and the circuits are in resonance with 

 each other. 



The old form of wireless telegraphy based upon such 

 mutual induction between closed coils, as in the arrangement 

 suggested by Trowbridge and Stevenson, or the parallel wire 

 method of Preece, Rathenau and others, employed relatively 

 low frequency currents because the receiver used was the 

 telephone, and the frequency was therefore limited by the 

 range of audition. Even when the circuits were put in 

 resonance, as by Lodge, the difficulties connected with the 

 disturbance of commercial telephony restricted the possibilities 

 of its use apart from other considerations. 



One object of the present experiments was to obtain data 

 for an opinion whether such inductive wireless telegraphy 

 could be improved by the use of electric oscillations of high- 

 frequency in completely non-earthed circuits so that no 

 disturbance of telephones or telegraphs could possibly arise 



* Moreover, just as in the case of the Hertzian oscillator true radiation 

 or detachment of energy only takes place ahout \ or \ a wave-length 

 from the oscillator, so in the case of the closed or magnetic oscillator true 

 radiation effects can only be produced at a similar distance from it. 



