90 Dr. B. van der Pol : Value of Conductivity of Sea- Water 



lis an oscillatory circuit in which high-frequency currents 

 are generated by the aid of a three-electrode vacuum-tube. 

 These currents induce oscillations in circuit II which is tuned 

 to I by aid of the Duddell t her mo-galvanometer Th, having a 

 heater resistance of 3*8 O. By means of the paraffin switches 



Fig. 1. 



us 

 > 



< 



> 



T 1 



o 





abed and efg h k either S 



or 



the terminals of the condenser C 2 . 



R can be connected across 

 R consists of a fine con- 

 stantan wire about 12 metres long having a diameter of 

 about "025 millimetre mounted zig-zag in such a way that the 

 distances between the eight parallel parts (each of 138 centi- 

 metres length) were 26 millimetres. This form was given 

 to the wire in order to avoid parts at appreciably different 

 potentials being near together, so that a minimum chance was 

 present for dielectric currents shunting parts of the wire. 

 The other shunt S across the terminals of the condenser C 2 is 

 made up of a glass tube (5*8 millimetres diameter and 170 

 centimetres long) filled with an electrolyte the conductivity 

 of which is to be determined. Of the two platinum electrodes 

 in S the lower one was fixed while the top one could be moved 

 to a greater or less depth in the electrolyte. 



The experiments were carried out as follows. For a 

 constant coupling between I and II first a reading of the 

 galvanometer Th was taken with the constantan wire re- 

 sistance across the terminals of C 2 (connexions between b-c 

 sendf-g), This resistance was then replaced by the tube 



