138 C. A. HEILAND 
conductors below is much greater than the influence of poor con- 
ductors below. This would make this method a rather valuable ac- 
cessory to the Racom, if it is desirable to emphasize in the results 
the effects of good conductors, such as ore bodies or formations 
which are filled with salt waters. 
Figures which give the general values for the potential ratios in 
the Racom method have not been published, but it appears from the 
diagrams given by Lundberg (Fig. 20) that for the average con- 
ductivity ratios the potential-drop-ratio responses are approximately 
the same for a good conductor below as they are for a poor conductor 
below; for, as seen from Figure 20, for the assumed conductivity ratio, 
the potential ratio is 1.5 for a good conductor above and o.5 for a 
good conductor below; or, the deflections in the Racom method are 
equal and opposite for equal and opposite conductivity ratios. Hence, 
when plotting in the Racom method the potential ratios on a vertical 
axis and the formation boundaries in a horizontal position, a poor 
conductor manifests itself by a deflection of the ratio curve toward 
the right, and a good conductor appears as a deflection of the ratio 
curve toward the left. For a poor conductor below, the ratio is greater 
than one, and for a good conductor below, the ratio is smaller than 
one. 
The chief advantage of the potential-drop-ratio method lies in the 
ease with which the potential ratio indications, if plotted in a suitable 
manner, may be interpreted with reference to the depth. of formation 
boundaries. Although the potential-drop ratios, and hence also the 
relations between depth of boundary and maximum of indication, 
depend on the conductivity ratios of the formations involved, yet 
several empirical rules have been found to hold very well for the 
average conductivity ratios encountered in the field. 
In Koenigsberger’s method, the depth corresponding with a ratio 
maximum is approximately 14 a for conductivity ratios up to 1:10 
or 10:1. In the Racom method, the depth to the formation boundary 
is, under similar conditions, equal to 24 r. (The significance of the 
symbols is explained in Figure 19.) Hence, when we turn the ratio 
traverses through go° and plot the curves vertically on a geologic 
section, we have to stretch the vertical scale of the section to 3/2 in 
the Racom, and double it in Koenigsberger’s method. Or, if we want to 
leave the scale of the geologic section as it is, we have to reduce the 
distances in Koenigsberger’s method to 44 and the distances in the 
Racom method to 2 of their original values. These relations are well 
468 
