Phantom circuit


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1.(Elec.) The equivalent of an additional circuit or wire, in reality not existing, obtained by certain arrangements of real circuits, as in some multiplex telegraph systems.
References in classic literature ?
One uncanny device, which would seem to be a mere inventor's fantasy if it had not already saved the telephone companies four million dollars or more, is known as the "phantom circuit." It enables three messages to run at the same time, where only two ran before.