In 1874, inventors were already experimenting with ways to make the telegraph more efficient. These inventors include Julius Wilhelm Gintl and J. B. Stearns, who focused on sending one message in each direction down one wire at the same time. Neither one had made the technology commercially viable.
Their invention was known as the duplex telegraph, and Edison developed his own version. He took it one step further, and added the ability to send two messages in each direction at the same time (known as the diplex telegraph), leading to four simultaneous messages.
- Don Fulton (Electrical Engineer)
- Chicago Tribune