The principle of the method is based on measurement of the electric field induced in the ground with suitable electrode devices, constituted by two pairs of electrodes fixed in the ground (configuration called “quadrupole”). In the quadrupole a pair of electrodes constitutes the circuit for the induction of the electric field in the ground (current dipole: conventionally electrodes A and B). The other pair (potential of dipole: M and N) represents the measurement circuit of potential difference (ddp) generated in the ground by the passage of the current itself. By Ohm‘s law (modified) the resistivity value, characteristic of these materials, can be determined (p). The value of the resistivity of the materials mainly depends on the following characteristics: degree of saturation of the pores; porosity; presence and composition of the fluids; temperature; possible presence of organic substances (hydrocarbons, solvents, etc.); clay; degree of compaction. Each type of soil or rocky body shows a wide range of variation of their resistivity values, which depend on the degree of homogeneity, the level of alteration and, in case of rocks, the degree of fracturing. In all conditions, the presence of water always plays an important role, so much that sandy-loamy or gravelly-sandy soil, if saturated, are more conductive than the same materials on dry conditions.