On aerial telegraph-lines this increase in the intensity of the battery occasions no particular inconvenience, other than by tending to the more rapid destruction of the small copper coils, or helices, employed; but upon submarine lines it has the effect of increasing the static electricity, or electricity of tension, which accumulates along the surface of the gutta-percha covering of the conducting-wire, in the same manner as static electricity accumulates on the surface of glass, or of a stick of sealing-wax, by rubbing it with a piece of cloth.  The use of submarine or of subterranean conductors occasions, from the above cause, a small retardation in the velocity of the transmitted electricity.  This retardation is not due to the length of the path which the electric current has to traverse, since it does not take place with a conductor, equally long, insulated in the air; but it arises from a static reaction, caused by the passage of an intense current through a conductor well insulated, but surrounded outside its insulating coating by a conducting body, such as sea-water or moist ground, or even by the metallic envelope of iron wires placed in communication with the ground.  When this conductor is presented to one of the poles of a battery, the other pole of which communicates with the ground, it becomes charged with static electricity, like the coating of a Leyden-jar,—­electricity which is capable of giving rise to a discharge-current, even after the voltaic current has ceased to be transmitted.  Volta showed in one of his beautiful experiments, that, in putting one of the ends of his pile in communication with the earth, and the other with a non-insulated Leyden-jar, the jar was charged in an instant of time to a degree proportional to the force of the pile.  At the same time an instantaneous current was observed in the conductor between the pile and the jar, which had all the properties of an ordinary current.  Now it is evident that the subaqueous wire with its insulating covering may be assimilated exactly to an immense Leyden-jar.  The glass of the jar represents the gutta-percha; the internal coating is the surface of the copper wire; the external coating is the surrounding metallic envelope and water.  To form an idea of the capacity of this new kind of battery, we have only to remember that the surface of the wire is equal to fourteen square yards per mile.  Bringing such a wire into communication by one of its ends with a battery, of which the opposite pole is in contact with the earth, whilst the other extremity of the wire is insulated, must cause the wire to take a charge of the same character and tension as that of the pole of the battery touched by it.

These currents of static induction are proportional in intensity to the force of the battery and the length of the wire, whilst an inverse relation is true as regards the length of the conductor with the ordinary voltaic current.

Professor Wheatstone proved, by actual experiment, that a continuous current may be maintained in the circuit of the long wire of an electric cable, of which one of the ends is insulated, whilst the other communicates with one of the poles of a battery, whose other pole is connected with the ground.  This current he considers due to the uniform and continual dispersion of the statical electricity with which the wire is charged along its whole length.