Edison patentIn 1878, Thomas A. Edison was issued a patent for “Quadruplex-Telegraph Repeaters” (U.S. No. 209,241). This invention is an improved method for one quadruplex circuit to repeat into another quadruplex circuit. The patent describes the electromagnets, local circuits, switches and connections. The circuits work into and operate each other, so that the message are repeated automatically into one circuit by the receiving instrument of the other circuit, instead of the finger key being operated by hand.