ADVANCES IN OIL PROSPECTING 93 
Swedish American Prospecting Corporation, and a number of en- 
couraging results were obtained on geologic structure. 
The object of the writer is to give a preliminary account of some 
of the results obtained, and to present a review of the entire field, 
covering both technique and results obtained by other authors. 
As our activities are not limited to research in electrical prospect- 
ing alone, the work has been carried through a comparatively great 
length of time, and various associates of the writer have been en- 
gaged in the work. Grateful acknowledgment is made for the con- 
tributions of data to T. A. Manhart, C. D. Keen, J. A. Malkovsky, 
D. H. Griswold, to the Swedish American Prospecting Corporation 
for part of the equipment, and to Harry Aurand and R. Clare Coffin, 
of the Midwest Refining Company, for permission to use some of the 
data and experience which this company has obtained in resistivity 
work. 
As the name indicates, resistivity methods are electrical methods 
in which the variation of resistivity is measured on the surface. Nu- 
merous methods are available for measuring resistivities, either in the 
well known resistivity bridges for D. C. or A. C., or by the use of 
ohmmeters, or finally, by separate measurements of voltage drop and 
current. As for known or constant current, the resistivity follows 
immediately from the potential distribution, all methods for the 
determination of potential differences or potential ratios on the sur- 
face, the so-called surface-potential methods, may also be included 
under the heading of resistivity methods. 
It is not surprising that attempts were made rather early to use 
the simple idea of resistivity measurements in prospecting. As early 
as 1900, Brown and McClatchey applied for a patent on resistivity 
measurement in this country, and at the same time Daft and Wil- 
liams, in their English and American patents, suggested the use of 
potential-difference observations for resistivity work. W. Petersson 
(ref. list No. III,) describes a qualitative resistivity method for the 
location of ore, consisting of a buzzer and telephone, the intensity of 
the sound received being an indication of ground conductivity. The 
method was used successfully in Sweden in 1906. 
The early attempts at the resistivity method were, however, only of 
a qualitative nature, as neither potential differences for fixed electrode 
spacings, nor even equipotential lines were observed. 
The credit for making the first systematic studies of ground re- 
sistivities goes to C. Schlumberger, who began work on the method in 
423 
