Stead// Electric Oscillations in Closed Circuits. 



671 



an element of difficulty in connexion with long-distance radio- 

 telegraphy, or else on account of the limited or continually 

 changing distance between the sending and receiving station. 



The first-named author o£ this paper has therefore been 

 seeking for some years past for a method of testing receivers 

 within very moderate distances which can afford all the 

 advantages to be obtained by working over long distances 

 without any of the disadvantages. 



This has now been achieved by the use of closed electric 

 circuits or magnetic oscillators instead of electric oscillators. 

 In a paper read before the Physical Society on October 25th, 

 1907 (see Phil. Mag. Dec. 1907 or Proc. Phys. Soc. Lond. 

 vol. xxi. p. 47), " On Magnetic Oscillators as Radiators in 

 Wireless Telegraphy," by J. A. Fleming, the author gave two 

 f ormulse : one for the radiation in watts from a linear oscillator 

 of the Hertzian type of length I, and the other from a square 

 closed circuit of area S, on the assumption that the oscillations 

 were persistent oscillations having a root-mean square value 

 a and a frequency N. These formulas were as follows : — ■ 



•W = 87 x 10~ 2( WN 2 (for the open or electric oscillator). 

 W=4xlO- 38 SVN 4 (for the closed or magnetic oscillator). 



In the above formula? W stands for the radiation in watts, 

 I for the length of the linear oscillator, and S for the area of 

 the closed or magnetic oscillator. 



These formulae show that in the case of the open or 

 electric oscillator the power radiated varies as the square of 

 the current-strength and as the square of the frequency, 

 whereas in the case of the closed or magnetic oscillator it 

 varies as the square of the current, but as the fourth power 

 of the frequency. Hence, for any such frequencies as are 

 used in radiotelegraphy and for such dimensions as are 

 generally possible, an open or linear oscillator has much 

 greater radiative power than a closed oscillator of about the 

 same linear dimensions. Accordingly, if two closed-circuit 

 oscillators are placed at a certain distance apart and oscil- 

 lations set up in one of them, and the other one used as a 

 receiving-circuit, the current in the receiving-circuit can be 

 made extremely feeble when the oscillators are separated by 

 not more than a few hundred yards, and we can avail our- 

 selves of such a means to provide what is the equivalent to 

 two radiotelegraphic stations with open or linear oscillators 

 separated by many hundreds of miles. The convenience, 

 therefore, of the closed or magnetic oscillator is very great 

 because it is possible to set up in an ordinary building, such 

 as a College or Technical Institution, two square circuits, 

 both under cover and within a reasonable distance of each 



