The theory, construction, and field use of a direct current potentiometer for measuring earth resistivity
The fundamental theory underlying direct current methods of measuring "apparent" earth resistivity and of interpreting these field measurements to obtain the actual resistivities of the parts of a composite earth is extensively reviewed. The three main types of apparatus used in...
Internet
https://thesis.library.caltech.edu/5594/1/Doolittle_rc_1940.pdfDoolittle, Russell Carter (1940) The theory, construction, and field use of a direct current potentiometer for measuring earth resistivity. Master's thesis, California Institute of Technology. doi:10.7907/D941-WY06. https://resolver.caltech.edu/CaltechTHESIS:03122010-083823737 <https://resolver.caltech.edu/CaltechTHESIS:03122010-083823737>