Simultaneous telephony and power transmission over the same wires
A 1906 University of Illinois engineering thesis by Thomas Hamer Amrine and Charles Clement Carr on carrying telephone signals and power current on one set of wires, written for faculty examiners. Its plates are hand-inked circuit schematics on tinted paper, with coils drawn as loose spirals, resistors as zigzags, and lettered labels for transmitters, batteries, condensers and lamps.
