РЕБЯТ ПОМОГИТЕ!!ТОЛЬКО НЕ НАДО ОНЛАЙН ПЕРЕВОДЧИКА!!!Telegraphy.
Electricity completely changed communications. Once it was discovered
that electric current flows along a wire, it seemed possible that it could be
used for messages. As long as two places were connected by a wire
electric impulses could be sent along it. It meant that people were able to
send messages a long way at great speed. The new way of communication had a lot
of advantages and by the end of the 19th century cables were laid
all over the world.
Samuel Morse, one of the most famous people in communications, invented
a special code, which we call now "the Morse code". He thought of
using short and long electric impulses. Combining different sets of impulses he
made a code for the whole alphabet, and the numbers from 0 to 9. This code, was
the easiest and the fastest to transmit.
Later on the necessity aroused to increase the speed of sending
messages. People decided to use the fact that current could flow one way round
the circuit or the other. A new system called double current working" was
worked out According to this system a dash and a dot are impulses of the same
length but of different directions.
Then a machine was invented to send typewriter messages over a telegraph
circuit. Such machines are called teleprinters or teletypes and use
International 5-unit code instead of the Morse code. Each letter or figure is
made up of five impulses of electric current, either positive or negative, all
letters being the same length in time. A teleprinter has a keyboard and every-
time one of the keys on the keyboard is pressed it sends the five impulses that
make one letter or figure.
As most modern systems use alternating current, one line can be used to
send many messages at the same time. It is possible if each message is sent out
at a different frequency. This allows high-speed telegraph communication as
well as transmission of written messages.