CONTEMPORARY ADVANCES IN PHYSICS 



587 



current in the circuit (measured by the detector) passes through a 

 maximum at a certain setting of the capacity. At the attainment of 

 this maximum, the system is said to be in resonance. 



In Szekely's experiments, the adjustable condenser was set to 

 produce resonance in three different conditions: in case (a) the ioni- 

 zation-condenser was entirely disconnected; in case {h) it was con- 

 nected, but there was no direct-current discharge flowing in the tube, 

 and the air was not ionized; in case (c) it was connected, and the air 

 was ionized by the direct-current discharge. The values Ca, Cb, Cc 

 of the adjustable capacity were measured at resonance under the 

 three conditions; their differences give the values of the capacity of 



DETECTOR 

 • I 



xsmmm^ 



SOURCE OF 

 HIGH FREQUENCY 



Fig. 2 — Illustrating a method for measuring dielectric constant and conductivity 

 of an ionized gas (between the plates of the "ionization-condenser")- 



the ionization-condenser (plus that of its leads, which apparently is 

 a large part of the total) when the gas is ionized and when it is not. 

 Out of these data one may calculate the dielectric constant of the 

 ionized gas. As for the conductivity: the values imb and imc of the 

 high-frequency current at resonance are different in cases (b) and (c), 

 smaller in the latter. After measuring imc, one may return to condition 

 (J) — shutting off the direct-current discharge — restore the resonance, 

 and reduce imb to the value just found for imc by adding resistance to 

 the circuit. From the amount p of added resistance which is necessary 

 to achieve this, one may calculate the resistance between the con- 

 denser-plates when the air is ionized; and thence — taking account of 

 the size and shape of the plates and the distance between them— 

 the conductivity of the ion-populated air. 



Everything thus is apparently provided for testing the expressions 

 and determining the constants derived from the theory of electrons 



