The object of this paper is to place on record the results of tests carried out at three different sites in England at which measurements were made of the mutual impedance between two earthed circuits. Results are given for different separations from 5 to 800 metres and for frequencies form 5 to 00 metres and for frequencies from 200 to 3 000 cycles per sec. The results are shown to be in good agreement with the theory on this subject,and the resistivity of the earth was found to be 250 ohms/cm3at one site and 6 000 ohms/cm2at the others.