356 Dr. Baltb. van der Pol on Measuring without Electrodes 



JX, a resonance position of the slider K being always possible 

 in tins range. 



Kir. 3. 



7jT 



\t 



T 



The discharge-tube had a thin paper scale stuck to it over 

 the whole length so that both the positions of the various 



Fig. 4. 



parts of the glow-discharge and the positions of the tube 

 with regard to the Lecher system could be determined. In 

 this way it is possible by sliding the discharge-tube vertically 

 through the parallel wire system at A and at the same time 

 taking the galvanometer readings, to measure the conductivity 

 at different parts of the tube with a simple apparatus and 

 without the disturbing effects due to separate test-electrodes 

 brought into the discharge. 



