Waves, tides and ocean currents might not be expected to produce electric currents, but by moving water, as a conductor, through the Earth's magnetic field they do in fact produce measurable voltages and flows of electricity. Young, Gerrard and Jevons, who made the first detailed study of this phenomenon, thought it conceivable that measurements of electric potential gradient might be used to estimate the drift of a ship at sea, and Von Arx showed how indications from electrodes towed behind the Research Vessel Atlantis were used to keep her on a direct course from Bermuda to Woods Hole, across the Gulf Stream. In recent years the method has been used extensively in studies of ocean currents and more ships might use it if the necessary equipment were readily available.