A basic telegraph system (a key, a battery, a wire, and a sounder) suffered from limitations on the distance over which signals could be transmitted, primarily due to the resistance of the wire itself and the earth ground return.  The message could be received and resent by any number of intermediate stations, but this slowed the process, tied up the lines (and operators), and was error prone. 

To overcome these problems, repeaters were used to automatically regenerate the signals.  A basic repeater was just a relay and a battery, but as more advanced telegraph systems evolved, repeater technology had to evolve as well.

The unit shown here is one of a pair of identical devices that would have constituted a single repeater station.  The inventor claimed it offered significant speed advantages over earlier designs.