The telegraph is a remotely controled device to display some kind of information. There
are very simple ones which only signal on or off, or go no go etc. Think on the signals
on a railway track. Other ones may display different messages like the telegraph on a
ship to give orders from the wheelhouse to the engine room. Time tables at railway
stations or airports are telegraphs.
For communication purposes an optical systems was used. The frenchman Claude Chappe
created a pointer system with legs for the alphabet. There was a system in France and other
countries.
With the invention of electricity a device come into use which could write dots and dashes
on a strip of paper just the same manner the electric curcit was closed by a switch.
Later on a typwriter was connected to the telegraph lines and one could
write on his telex device to some one far away. The signals were sent via 2 wires to a similar
telex device.
Read whole telegraph story in
Wikipedia
