Telegraphy (from the
Greek words (τηλη) = far and (γραφειν) = write) is the long-distance transmission of written messages without physical transport of letters, originally by changing something that could be observed from a distance (
optical telegraphy). Radiotelegraphy or wireless telegraphy transmits messages using
radio. Telegraphy includes recent forms of
data transmission such as
fax,
email, and
computer networks in general. (A telegraph is a machine for transmitting and receiving messages over long distances, i.e., for telegraphy. The word telegraph alone 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 using a
spark gap).
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