. American telephone practice . end, or from the ground at each end to the receiver,y, thus in no case causing *ts diaphragm to vibrate. The sameresults were obtained by grounding the point E through an or-dinary telephone. The receiver, y, still remained silent, while xand z were both affected to an equal degree. It was also found that opening the central point of the line, C D,produced no effect whatever on the existing conditions; the noisesin the receivers, x and z, were plainly heard and of equal loundess. Many other experiments were tried, the results in each case TELEPHONE LINES. 163 po
. American telephone practice . end, or from the ground at each end to the receiver,y, thus in no case causing *ts diaphragm to vibrate. The sameresults were obtained by grounding the point E through an or-dinary telephone. The receiver, y, still remained silent, while xand z were both affected to an equal degree. It was also found that opening the central point of the line, C D,produced no effect whatever on the existing conditions; the noisesin the receivers, x and z, were plainly heard and of equal loundess. Many other experiments were tried, the results in each case TELEPHONE LINES. 163 pointing conclusively to the induction from voice currents being ofan electrostatic instead of an electromagnetic nature. There is no doubt, however, that induction from wires carryingheavy currents, such as are used in lighting and power work, ispartly due to electromagnetic effects, and this can be easily provenby experiments similar in nature to those described. The one remedy for all the troubles due to disturbing noises from. FIG. 143.—METALLIC CIRCUIT LINE. any of the causes is to make the line a complete metallic this is meant a circuit having both its sides formed of a wire,each wire being individual to the circuit and not forming a portionof other circuits. A metallic circuit line connecting two telephonesis shown in Fig. 143. This alone, however, will not completely stop noises from mostof the causes, and additional precaution must be taken, by makingthe two sides of the circuit alike in all respects and properly trans-posing them at frequent intervals, in order that they may be as DISTURBING WIRE P=^c 3>o=^) FIG. 144.—ELECTROMAGNETIC DISTURBANCES. nearly symmetrical with respect to the disturbing source or sourcesas possible. Merely making the line a metallic circuit, as in Fig. 143, doesnot give complete freedom from inductive troubles from other wires,whether the induction be electromagnetic or electrostatic. Con-sidering the question from the stand
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