for Currents of Frequencies in Wireless Telegraphy. 91 



filled with electrolyte by connecting a-b and e-f. The 

 length of the pnth of the current through the latter was 

 then altered by moving the top electrode till an equal 

 deflexion of Th was obtained. The high-frequency resistance 

 of S was then equal to that of R. Immediately afterwards, 

 in order to avoid changes in temperature, connexions were 

 made between d-a-c, e-h, and g—k so that S and R formed 

 two branches of an ordinary Wheatstone bridge, the re- 

 maining two branches being P and Q, one of which was 

 variable. A slowly alternating current of about 90 cycles 

 per second, drawn from a small transformer fed by the town 

 supply, was afterwards sent through the bridge, which was 

 balanced by aid of the telephone T. The ratio of the resist- 

 ances R and S for slowly alternating currents at once gave 

 the ratio of the resistance of the electrolyte for high- 

 frequency currents to the resistance for low-frequency or 

 direct currents. 



A word may be said about the accuracy and the possible 

 errors inherent to this method. The resistance of the con- 

 stantan wire is assumed to be the same for high and low 

 frequencies. The skin effect in such a fine wire of a com- 

 paratively high specific resistivity does not alter the apparent 

 resistance for a frequency of 10 6 more than one part in a 

 million compared with the value for steady currents, and the 

 same reasoning can be applied to the tube filled with sea- 

 water. It is further well known that the conductivity of 

 metals is independent of the frequency in the range of 

 to 10 6 , so that no error is introduced by assuming the 

 resistance of the constantan wire to be constant over the 

 range of frequencies used. The unavoidable differences 

 of self-induction in S and R have only a very small in- 

 fluence on the results, as can be seen from the following 

 consideration. 



Fig. 2. 



With the notation of fig. 2 the currents i x and i 2 in the 

 main circuit and the shunt across the condenser C respectively 



