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Telegraphy is the long-distance transmission of written messages
without physical transport of letters. It is a compound term formed
from the Greek words tele (τηλε) = far and graphein (γραφειν) =
write. Radiotelegraphy or wireless telegraphy transmits
messages using radio.
A telegraph is a device for transmitting and receiving messages
over long distances, i.e., for telegraphy. The word telegraph alone
now generally refers to an electrical telegraph. Wireless telegraphy
is also known as "CW", for continuous wave (a carrier modulated
by on-off keying), as opposed to the earlier radio technique of
using a spark gap.
A telegraph message sent by an electrical telegraph operator or
telegrapher using Morse code (or a printing telegraph operator
using plain text) was known as a telegram. A cablegram was a
message sent by a submarine telegraph cable, often shortened to
a cable or a wire. Later, a Telex message was a telegram sent by a
Telex network, a switched network of teleprinters similar to a telephone network.