violent electrical disturbances of the nature of transient currents, which rush in one direction or another, and by which telegraphic lines, and particularly long submarine lines, are constantly troubled. The origin and nature of earth currents are not thoroughly understood, but they are found to be very intimately connected with the disturbances of terrestrial magnetism, called magnetic storms, and these, it is well known, are closely connected with the appearance of the aurora borealis and with the occurrence of the sun's spots. See AURORA BOREALIS.