possible to telegraph
around the world in this way.

If it were possible to imitate the telegraph repeater in telephony,
attenuated voice currents might be caused to actuate it so as to send
on those voice currents with renewed power over a length of line,
section by section. Such a device has been sought for many years, and
it once was quoted in the public press that a reward of one million
dollars had been offered by Charles J. Glidden for a successful device
of that kind. The records of the patent offices of the world show what
effort has been made in that direction and many more devices have been
invented than have been patented in all the countries together.

Like some other problems in telephony, this one seems simpler at first
sight than it proves to be after more exhaustive study. It is possible
for any amateur to produce at once a repeating device which will relay
telephone circuits in one direction. It is required, however, that in
practice the voice currents be relayed in both directions, and
further, that the relay actually augment the energy which passes
through it; that is, that it will send on a more powerful current than
it receives. Most of the devices so far invented fail in one or the
other of these particulars. Several ways have been shown of assembling
repeating devices which will talk both ways, but not many assembling
repeating devices have been shown that will talk both ways and augment
in both directions.

[Illustration: Fig. 36. Shreeve Repeater and Circuit]

Practical repeaters have been produced, however, and at least one type
is in daily successful use. It is not conclusively shown even of it
that it augments in the same degree all of the voice waves which reach
it, or even that it augments some of them at all. Its action, however,
is distinctly an improvement in commercial practice. It is the
invention of Mr. Herbert E. Shreeve and is shown in Fig. 39.
Primarily it consists of a telephone receiver, of a particular type
devised by Gundlach, associated with a granular carbon transmitter
button. It is further associated with an arrangement of induction
coils or repeating coils, the object of these being to accomplish the
two-way action, that is, of speaking in both directions and of
preventing reactive interference between the receiving and
transmitting elements. The battery _1_ energizes the field of the
receiving element; the received line current varies that field; the
resulting motion