132 C. A. HEILAND 
II. APPARATUS 
a. GENERAL: POWER SOURCES 
Potential-drop-ratio measurements may be made with both 
D.C. and A.C. Koenigsberger has used both types of current, while 
the Swedish American employs only A.C. If D.C. is used, a number 
of B-batteries are sufficient, if the required depth penetration is not 
great. Otherwise, a gasoline engine D.C. generator is more advanta- 
geous for greater depth of exploration. The current should be inter- 
rupted by a commutator similar to the one employed in the Gish- 
Rooney apparatus, so that effects of polarization and stray currents 
are eliminated. As will be stated later, the Gish-Rooney equipment 
itself may be employed for potential-drop-ratio determinations (with 
slight modification) for simple problems, although the accuracy 
furnished by the potentiometer customarily employed in this ap- 
paratus is not sufficient for many purposes. 
For the potential ratiometers as used by the Imperial Geophysical 
Survey and the Swedish American Prospecting Company, alternat- 
ing current of about 500 cycles is required, which for small depths of 
penetration is furnished by a buzzer operated from a storage battery 
(Fig. 23) while for greater distances and unfavorable contact con- 
ditions, a 500 A.C. generator is preferable. It must be borne in mind, 
however, that the use of a stronger power source alone with average 
frequencies does not bring about a greater depth penetration, as the 
latter decreases with the frequency employed; hence, for great depth 
penetrations, the frequency has to be considerably lowered, which 
then also would require a change in the dimensions of resistances and 
inductances in the ratiometers, or else commutated D.C. should be 
used. 
b. KOENIGSBERGER’S AND OTHER D.C. METHODS 
Koenigsberger indicates in his publication (ref. list No. IV2) in a 
general way a number of arrangements which he has used for the 
measurement of potential-drop ratios, but does not go into details 
with reference to apparatus employed. When using D.C., the potential 
differences A—B and B—C may, of course, be measured independ- 
ently by a potentiometer and their ratio may be formed by computa- 
tion. For this purpose, a regular Gish-P soney equipment may be 
employed, with an electrode arrangement identical with that used 
in the single-probe method (Fig. 7, type JJa). The potential differ- 
ence between the points B and C is measured in the usual way; then 
