180 PROCEEDINGS OF THE AMERICAN ACADEMY 



adoption by either the power companies or the telephone companies 

 of entire metallic circuits, in which the earth plays no part. If this is 

 not possible, a system of neutralization for the inductive disturbances 

 might be adopted as follows. Let a shunt circuit from the electric 

 light wire or the wire carrying the current for motors be led into 

 a station through which also passes the telephone wire. The resist- 

 ance of this shunt or derived circuit can be made suitable for the pur- 

 pose. In all cases it reduces the resistance of the main line, and is 

 therefore not prejudicial. On this shunt can be arranged a fixed coil, 

 and on a neighboring telephone wire a movable coil of no self-induc- 

 tion. Let this movable coil be placed in front of the fixed coil in the 

 motor circuit, and let it be turned until the. mutual induction between 

 it and the fixed coil neutralizes the induction produced at all points 

 along the telephone circuit. Each telephone wire would need its 

 movable coil, and to every movable coil would correspond a fixed coil 

 in the shunt of the motor circuit. The operator at the central sta- 

 tion could adjust the movable coils until the disturbances arising from 

 induction at various points along the line are neutralized. 



