ADVANCES IN OIL PROSPECTING 133 
the electrode in C is left there and the electrode wnich was at B is 
moved to a next point, say D, which has the same distance from C, as 
B has from C. The curves shown in Figure 33 have been obtained in 
this manner. The method is not very accurate, as the surface and con- 
tact resistances enter considerably. 

FIG. 21 
a: Detailed circuit diagram of Racom compensator 
b: Schematic circuit diagram of same 
Koenigsberger uses also a modification of this method: The central 
electrode is left permanently connected to the potentiometer and the 
other electrodes, B and C, are connected alternately with it by means 
of a commutator. The ratio of the deflections gives the potential 
463 
