Measurement of Electrode-Potentials 



aq\ 



ids. 



27 



containing the telephone between the junction of the two con- 

 densers and T, a second auxiliary electrode P is required in 

 the liquid contained in the annular space <?, fig. 1. It was 

 found that an electrode of ordinary smooth platinum answered 

 perfectly well for this purpose. The current for these 

 measurements was derived from a small induction-coil, a 

 rough condenser being interposed between it and one of the 



Fig. 3. 



junctions. The method of working consisted in giving the 

 two standard condensers A and B suitable values, say 500 

 and 20 millemicrofarads, and finding the value wij of the 

 variable resistance M taken from a dial-resistance-box that 

 produced a minimum in the telephone. The smaller of the 

 two condensers, B, i. e. the one on the anode side, was then 

 altered to its r-fold value 20 r millemicrofarads, the other 

 condenser being left unaltered. The new resistance m 2 was 

 now determined, which produced a minimum in the telephone. 

 The required resistance x from the cathode to T is then mani- 

 festly derived from the equation 



its value being 



x + m L 1 

 as + m 2 ~~ r 



# = 



m 2 — rm ] 



The following are details of the apparatus shown in figs. J 

 and 2 that must be specially referred to. The cathode and 



