Each letter of the alphabet is printed around the top
edge, and has a corresponding coil of wire. A character is sent by
passing a current through the corresponding coil, creating a magnetic
field which turns the needle to indicate which character is being sent.
This device is one of a generation of telegraph
devices invented before the development of Morse code. The
response of the needle is very slow and each alphabetic character
requires a separate wire between the transmitter and receiver, or 26
wires in all. "Needles" to say, (sorry) these early telegraphs
were not very practical and saw little commercial use.