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Natural earth currents measured with microammeter and potentio
Lines of current flow and equipotential lines
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100-foot intervals alternating current amperes angles measured azimuth battery Bureau of Mines coil for minimum coil survey coil vertical conducting layers conductors current flow cycles A. C. Detector depth detecting coil difference of potential dip of flux direction earth currents earth resistivity east to west east-west line effect electrical methods electrodes electromotive force ellipse elliptic polarization equipotential lines feet between stakes frequency galvanometer geophysical prospecting Gish-Rooney grounded at 100-foot Hill proving ground indicated instrument insulated wire Interval extends iron stakes leapfrog method Line run magnetic field magnetite measured from vertical megger method megger read microammeter minimum signal strength natural currents natural-current north to south north-south line obtained ohm-centimeters ohms parallel wires Pittsburgh coil placed plane of coil plane table porous pots potentiometer region right angles shown in Figure stake intervals stake resistance station strike and dip telephones tilt tion vertical loop volts west line