94 C. A. HEILAND 
about 1913. The first year in which he applied the method of resis- 
tivity mapping was 1920, and numerous structural studies for com- 
mercial purposes were carried out by this company in subsequent 
years. 
Schlumberger obtained a French patent on his resistivity method 
on September 15, 1925. 
Considerable interest was attracted at the same time to an identi- 
cal method, described by Gish and Rooney, December, 1925 (ref. 
list No. III:), which was used in determining earth resistivities for 
the study of earth-current and related magnetic phenomena. Their 
method was based on Wenner’s method of measuring earth resistivity, 
published in rors (ref. list No. Il). 
The Gish-Rooney method was taken up with considerable interest 
by a number of mining companies; primarily, the Michigan School 
of Mines has been largely responsible for the advances of this method 
in mining. The papers written by W. O. Hotchkiss, J. Fisher, and 
W. J. Rooney (ref. list No. IIIs) in 1929, report on the results ob- 
tained in the Michigan copper and iron country. 
At about the same time, the U. S. Bureau of Mines became inter- 
ested in resistivity work, and codperated with A. S. Eve and D. A. 
Keys in the experimentation with electrical methods. Their studies 
have continued up to the present time, and the results are recorded 
in numerous papers, written by F. W. Lee, A. S. Eve, D. A. Keys, and 
J. H. Swartz (ref. list Nos. IIs, Jia TIT3 ,4,9,19,29,30,33,37) + 
A number of fundamental papers also appeared on the theoretical 
foundation of the method, written by J. N. Hummel, W. Weaver, 
D. O. Ehrenburg, Lancaster-Jones, Tagg, R. J. Watson, T. Roman, 
L. J. Peters, J. Bardeen, S. Stefanesco, and C. and M. Schlumberger 
(ref. list, section II). 
Meanwhile, in 1928, an important application of the resistivity 
method had been found, the determination of depth to bedrock in 
dam sites. Papers by I. B. Crosby and E. G. Leonardon (ref. list 
12,18, 20,25,32,35) deal with this application. 
As far as the use of resistivity methods in oil work is concerned, the 
Schlumberger Company had proved the practicability of the method 
in structural studies since 1921. Work was then begun in the Pechel- 
bronn oil region and continued until 1926. In Roumania, commercial 
work was carried out, among others, for the Steaua Romana in 
1923-1926. Salt domes were located in the Alsace region in 1926-1927. 
Resistivity prospecting for oil structures was begun in the United 
424 
