140 C. A. HEILAND 
even under favorable geologic conditions, the deflections of the cur- 
rent lines were usually small and therefore the claimed effects could 
be readily disputed. In addition, this company made their claims 
on the basis of some work which was carried out at comparatively 
great depth and under complex geologic conditions, so that it was 
easy for their opponents to go so far as to state that there was no 
telling whether the observed deflections came from salt. water or from 
oil. 
The opponents of the Elbof theory, notably Ambronn, then went 
to the other extreme in trying to prove that it was theoretically im- 
possible, under any circumstances, to detect oil directly with alternat- 
ing current. Ambronn claimed that the conductivity ratio required 
for electrical prospecting by means of alternating current should be 
at least 1,000 for such a change to be detectable, a figure which has 
been proved to be much too high by actual experience obtained since 
with the potential and resistivity methods. In addition, Heine and 
Hunkel proved theoretically that the formulas used by Ambronn for 
his proofs were in error. 
Lately, the Elbof company has also taken up, in addition to their 
electromagnetic method, the study of the potential-drop-ratio and 
resistivity methods; the results obtained in sevesal areas have been 
published by Gella and Koenigsberger (ref. list III23; IV2). Unfor- 
tunately, in both publications, no curves are given and this is prob- 
ably the reason why these more recent claims of the Elbof company 
and Koenigsberger, which are based on reliable and favorable tech- 
nique, have passed almost unnoticed. The figures given for the re- 
sults obtained with the potential drop ratio at the oil field of Oberg 
in Germany are given in such manner that the reader who is not 
familiar with the locality can not form an opinion as to the extent to 
which the claims advanced are justified. The writer has made an at- 
tempt to use as many of Koenigsberger’s data as possible and to 
superimpose them upon the geologic section; the results are repre- 
sented in Figure 4o and are discussed at the end of this paper. 
While working with the potential-difference method, the Elbof 
company found that in certain areas where the oil-bearing strata are 
overlain by porous strata such as sands and sandstones, the gas had 
in many places migrated into them from the strata below, had dis- 
placed the salt water and had thus increased considerably the thick- 
ness of the strata acting as poor conductors. This may make it possible 
in some places to apply the electrical method to advantage, but it is, 
470 
