In both telegraphy and telephony, the longer the line the weaker the
current which is received at the distant end. In both telegraphy and
telephony, there is a length of line with a given kind and size of
wire and method of construction over which it is just possible to send
intelligible speech or intelligible signals. A repeater, in
telegraphy, is a device in the form of a relay which is adapted to
receive these highly attenuated signal impulses and to re-transmit
them with fresh power over a new length of line. An arrangement of two
such relays makes it possible to telegraph both ways over a pair of
lines united by such a repeater. It is practically possible to join up
several such links of lines to repeating devices and, if need be, even
submarine cables can be joined to land lines within practical limits.
If it were necessary, it probably would be 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