Later on this knowledge gave him work which enabled him to gain experience as a telegraph operator, which in turn led to his invention of the quadruplex telegraph.
"The Girl Wanted"
Nixon Waterman
This suited me, and I started in and succeeded in making such an instrument, which had in it the germ of my quadruplex now used throughout the world, permitting the despatch of four messages over one wire simultaneously.
"Edison, His Life and Inventions"
Frank Lewis Dyer and Thomas Commerford Martin
They all led up to the quadruplex.
"Edison, His Life and Inventions"
Frank Lewis Dyer and Thomas Commerford Martin