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but has largely been superseded by the code system of the American Standard
Code for Information Interchange (ASCII).
Baudot's system was the forerunner of the teleprinter, or teletypewriter (also
known as the teletype). Earlier telegraph machines fitted with keyboards and type
wheels produced tape on which stock-market prices were transmitted. The
machines used for this were known as tickers, and the tape was called tickertape.
Around the end of the 19th century and the beginning of the 20th, the teleprinte,
was developed through the pioneering work of the Britons Donald Murray and
Frederic* Creed, and the American Charles Krumm Teleprinters continue to play a
vital role » business. They have been improved and speeded up and are to be
found in most offices , especially those of international companies-* Teleprinters
combined in networks form what is called the telex service.
The Telephone
The possibility of sending speech along a wire was known as early as the 17th
century. By the 1870s the idea of converting sound into an electric current that
could be sent along 3 metal wire was well-known, and several inventors were
rushing to make the first practical telephone. The Scots-born America "
Alexander Graham Bell succeeded in doing' this in 1875. Telephone lines and
services spread remarkably quickly throughout the*-world. State-run and privately
organized telephone networks now operate both nationally and internationally.
Though operator-j assisted calls are still made, most calls, even those over the
longest distances, are dialed direct and are connected automatically.
The principles on which Bell's telephone worked are not so very different from
the ones used by the telephone of today. The telephone consists of a transmitter in
the mouthpiece of the instrument that is connected by wires through an electricity
power supply to a receiver in the earpiece of the instrument at the other end. The
transmitter is a carbon microphone .The sound waves of the caller's voice are
carried to a diaphragm, which is thus made to vibrate in and out. The diaphragm,
which is made of thin, flexible plastic, forms the lid of a little "pillbox" packed
with grains of carbon, an element that is a good conductor of electricity. When
nobody is speaking, current flows smoothly and evenly through the grains. Sound
vibrations from the caller's voice, however, set the diaphragm moving in and out.
With each inward movement, the grains become more tightly packed together d
their resistance to the passage of the electric current is reduced. Thus the power
supply sends a larger current through the transmitter. With every outward
movement of the diaphragm. the grains become less tightly packed and their
resistance increases, reducing the strength of the current. Thus, when the caller 's
speaking, a varying electric current is sent along the wire to the distant receiver.
The receiver, in the earpiece of the telephone, consists of an electromagnet and
another thin, flexible diaphragm, this time made of soft iron. The ends of the
electromagnet are connected to the incoming wire carrying the message
transmitted from the caller Behind the electromagnet is a permanent steel magnet
that puts a steady, unvarying pull on the soft-iron diaphragm. When the electric
current passing through the coil of the electromagnet increases during a caller's
transmission, the electromagnet strengthens the effect of the permanent magnet,
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