Conduction signalling in the sea

The concept of conduction signalling is that electric currents are injected into the sea by means of electrodes, producing resistive potential differences which are detected using another pair of electrodes at a distance. It is shown that even at low audio frequencies electromagnetic effects must be taken into account, and doing so leads to the conclusion,surprising at first sight, that the electrodes are largely incidental and that it is the wires connecting them which control the launching and detection of the signals.