. American telephone practice . FIG. 139.—GKOUNDED LINE. Disturbances on telephone lines from neighboring wires may beattributed to one or all of the following three causes: leakage, elec-tromagnetic induction, and electrostatic induction. Leakage may occur through defective insulation between thetwo circuits; or even when the insulation of the wires themselves ispractically perfect a heavy return current from a grounded circuit,such as of an electric railway, may, upon its arrival at the groundedend of the telephone line, have the choice of two paths, one throughthe telephone line, and the ot
. American telephone practice . FIG. 139.—GKOUNDED LINE. Disturbances on telephone lines from neighboring wires may beattributed to one or all of the following three causes: leakage, elec-tromagnetic induction, and electrostatic induction. Leakage may occur through defective insulation between thetwo circuits; or even when the insulation of the wires themselves ispractically perfect a heavy return current from a grounded circuit,such as of an electric railway, may, upon its arrival at the groundedend of the telephone line, have the choice of two paths, one throughthe telephone line, and the other a continuation of its path throughthe ground. This is the greatest source of trouble due to railwaywork, on grounded telephone lines. Electromagnetic induction on a telephone line is due to the factthat the line wire lies in the field of force set up by current flowingin the disturbing wire. About every wire carrying a current thereis a field of force, or magnetic whirl, consisting of closed lines 160 AMERICAN TELEPHONE P
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