Quadruplex telegraph invented by Thomas Alva Edison (1847-1931) in 1874. It could send and receive four telegraph messages simultaneously on a single wire, two signals in each direction. Engraving.
Quadruplex telegraph invented by Thomas Alva Edison (1847-1931) in 1874. It could send and receive four telegraph messages simultaneously on a single wire, two signals in each direction. Engraving.