Let a conductor, say a metallic sphere, be supported by a metal rod of negligible electric capacity whose other end is earthed.
This slip is then passed through a transmitter fitted with brush contacts and connected to the two line wires of a metallic loop. One circuit is formed by the loop itself, and a second, quite independent, by the two wires in parallel, earthed at each end.
In 1892, on the Bristol Channel, he established communication between Lavernock Point and an island called Flat Holme in that channel by placing at these positions insulated single-wire circuits, earthed at both ends and laid as far as possible parallel to each other, the distance between them being 3.3 m.
By stretching on the island and mainland parallel wire circuits earthed at each end, good telephonic communication over an average distance of 62 m.
If we suppose the cable interrupted at any place, and both sides of the gap earthed by connexion to plates, then the same conditions will still hold.