An infinite line source or current‐carrying cable on the surface of a flat homogeneous earth is considered. The integral formula, for the case of negligible displacement currents, is reduced either to tabulated functions or to a form suitable for numerical integration. A table of numerical values of these basic integrals is presented. We also show that, in principle, the relative location of the line source can be deduced from measurements of the subsurface field The results have possible application to mine rescue operation