680 Dr. J. A. Fleming on Magnetic Oscillators 



in the field of such a closed oscillator and the derivation of 

 the formula (10) for the radiation, it is unnecessary to go 

 over the ground again here. (See ' The Electrician,' vol. 59, 

 p. 936 et seq.) 



The object of the following experiments was to obtain 

 some information as to the actual distance-effects of closed 

 oscillators of certain dimensions, and to ascertain whether 

 true radiation was at all influential in producing the inductive 

 action of one closed oscillatory circuit on another at moderate 

 distances, or if the whole of the action could be accounted for 

 by ordinary electromagnetic or Faradaic induction. 



The following circuits were employed for this purpose : — 



Two pair of square circuits were constructed by winding a 

 few turns of highly insulated copper wire round a wooden 

 cross. 



One pair had sides 8 feet in length, each frame carrying- 

 two coils of 5 turns of 7/21 stranded insulated copper wire. 

 These will be referred to as the " large square coils." 



One pair had sides 2 feet in length, each frame carrying 

 one coil of 8 turns of the same sized wire. These are 

 referred to as the " small square coils." 



The experiments consisted in setting up continuous or 

 undamped oscillations in one of these coils by means of a 

 Poulsen arc and then measuring the current created in the 

 corresponding coil placed at a distance by means of the 

 Author's oscillation-valve or glow-lamp detector. The two 

 coils were placed at various distances and in various respective 

 positions. The coils themselves were erected or placed in 

 the large quadrangle of University College, London, As the 

 arc apparatus had to be placed indoors in the Electrical 

 Laboratory it was necessary to connect the coil used as a 

 transmitter or primary coil with the oscillation-producing 

 apparatus by means of a long pair of insulated parallel 

 copper (7/21) wires 14 cms. apart and 27^- feet or 836 cms. 

 long. 



The first step was to measure the inductance of these wires 

 for high frequency currents. Anderson's bridge method was 

 employed with a commutator as described by the Author*. 



The inductance of the parallel wires or tails above men- 

 tioned was found to be 50,9.10 cms., and that of one large 

 coil of 5 turns on the 8-foot square together with the tail 



* See J. A. Fleming, "A Note on the Measurement of Small Inductances 

 and Capacities," Phil. Mag. May 1904, p. 586. 



See also J. A. Fleming and W. C. Clinton, " On the Measurement of 

 Small Capacities and Inductances," Phil. Mag. May 1903, p. 493. 



