The problem of determining electrical earth conductivity from the surface, in the case where it is a function of the depth only, is solved by a perturbation method, which formally at least, allows the unperturbed functions to be perfectly arbitrary. Numerical work, however, is restricted to those functions which are available as solutions of the so‐called ``inverse'' problem, a group of which is given. Of this group the case in which the unperturbed conductivity varies exponentially is treated in detail and two examples showing the success of the method are presented. A numerical method of solving integral equations of the Laplace type, which occur in the above, is also submitted.