There were many attempts to make the telegraph more efficient, and Thomas Alva Edison’s quadruplex telegraph was the most famous among them.
Edison had been trying for many years to find a method to send two messages simultaneously over a single wire. Western Union adopted the duplex system developed by Joseph Stearns, which could send two messages in opposite directions, in 1872. William Orton, president of the company then asked Edison to invent other methods, too. Edison combined the duplex with the diplex system which sent two messages in the same direction, thus making it possible to send four messages simultaneously – two in each direction.
The quadruplex telegraph lost its importance later, with the coming of multiplex telegraphy that made it possible to send eight or more simultaneous transmissions, and the teletype machines.
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