Page:Arthur B Reeve - The Dream Doctor.djvu/105

 the other circuits in multiple. All three circuits are independent, too.

"The third telephone current enters the wires of the first circuit, as it were, and returns along the wires of the second circuit. There are several ways of doing it. One is to use retardation or choke-coils bridged across the two metallic circuits at both ends, with taps taken from the middle points of each. But the more desirable method is the one you saw me install this afternoon. I introduced repeating-coils into the circuits at both ends. Technically, the third circuit is then taken off from the mid-points of the secondaries or line windings of these repeating coils.

"The current on a long-distance line is alternating in character, and it passes readily through a repeating-coil. The only effect it has on the transmission is slightly reducing the volume. The current passes into the repeating-coil, then divides and passes through the two line wires. At the other end the halves balance, so to speak. Thus, currents passing over a phantom circuit don't set up currents in the terminal apparatus of the side circuits. Consequently, a conversation carried on over the phantom circuit will not be heard in either side circuit, nor does a conversation on one side circuit affect the phantom. We could all talk at once without interfering with each other."

"At any other time I should be more than interested," remarked Brixton grimly, curbing his impatience to be doing something.

"I appreciate that, sir," rejoined Kennedy. "Ah, here it is. I have the central down in the village.