An earth battery is a pair of electrodes made of two dissimilar metals, such as iron and copper, which are buried in the soil or immersed in the sea.
One of the earliest examples of an earth battery was built by Alexander Bain in 1841 in order to drive a prime mover—a device that transforms the flow or changes in pressure of a fluid into mechanical energy.
[1][2] Bain buried plates of zinc and copper in the ground about one meter apart and used the resulting voltage, of about one volt, to operate a clock.
Carl Friedrich Gauss, who had researched Earth's magnetic field, and Carl August von Steinheil, who built one of the first electric clocks and developed the idea of an "Earth return" (or "ground return"), had previously investigated such devices.
The Earth battery, in general, generated power for early telegraph transmissions and formed part of a tuned circuit that amplified the signalling voltage over long distances.
Some early experimenters did recognize that these currents were, in fact, partly responsible for extending the earth batteries' high outputs and long lifetimes.
[7] Lord Kelvin observed that such variables as placement of the electrodes in the magnetic field and the direction of the medium's flow affected the current output of his device.
In such an arrangement, the electrodes are not appreciably chemically corroded, even when they are in earth saturated with water, and are connected together by a wire for a long time.
[citation needed] In some cases, a pair of plates with differing electrical properties, and with suitable protective coatings, were buried below the ground.
To use the natural electricity, earth batteries fed electromagnets, the load, that were part of a motor mechanism.