26 September 2012
Rotary dial telephone
The first device allowing callers to connect their
telephones to other parties without the aid of an operator, the rotary
dial telephone preceded the touch-tone phone.
The people behind the invention:
Alexander Graham Bell (1847-1922), an American inventor
Antoine Barnay (1883-1945), a French engineer
Elisha Gray (1835-1901), an American inventor
Rotary Telephones Dials Make Phone Linkups Automatic
The telephone uses electricity to carry sound messages over long
distances. When a call is made from a telephone set, the caller
speaks into a telephone transmitter and the resultant sound waves
are converted into electrical signals. The electrical signals are then
transported over a telephone line to the receiver of a second telephone
set that was designated when the call was initiated. This receiver
reverses the process, converting the electrical signals into the
sounds heard by the recipient of the call. The process continues as
the parties talk to each other.
The telephone was invented in the 1870’s and patented in 1876 by
Alexander Graham Bell. Bell’s patent application barely preceded
an application submitted by his competitor Elisha Gray. After a
heated patent battle between Bell and Gray, which Bell won, Bell
founded the Bell Telephone Company, which later came to be called
the American Telephone and Telegraph Company.
At first, the transmission of phone calls between callers and recipients
was carried out manually, by switchboard operators. In
1923, however, automation began with Antoine Barnay’s development
of the rotary telephone dial. This dial caused the emission of
variable electrical impulses that could be decoded automatically
and used to link the telephone sets of callers and call recipients. In
time, the rotary dial system gave way to push-button dialing and
other more modern networking techniques.
Telephones, Switchboards, and Automation
The carbon transmitter, which is still used in many modern telephone
sets, was the key to the development of the telephone by Alexander
Graham Bell. This type of transmitter—and its more modern
replacements—operates like an electric version of the human
ear. When a person talks into the telephone set in a carbon transmitter-
equipped telephone, the sound waves that are produced strike
an electrically connected metal diaphragm and cause it to vibrate.
The speed of vibration of this electric eardrum varies in accordance
with the changes in air pressure caused by the changing tones of the
Behind the diaphragm of a carbon transmitter is a cup filled with
powdered carbon. As the vibrations cause the diaphragm to press
against the carbon, the electrical signals—electrical currents of varying
strength—pass out of the instrument through a telephone wire.
Once the electrical signals reach the receiver of the phone being
called, they activate electromagnets in the receiver that make a second
diaphragm vibrate. This vibration converts the electrical signals
into sounds that are very similar to the sounds made by the person
who is speaking. Therefore, a telephone receiver may be viewed
as an electric mouth.
In modern telephone systems, transportation of the electrical signals
between any two phone sets requires the passage of those signals
through vast telephone networks consisting of huge numbers
of wires, radio systems, and other media. The linkup of any two
phone sets was originally, however, accomplished manually—on a
relatively small scale—by a switchboard operator who made the
necessary connections by hand. In such switchboard systems, each
telephone set in the network was associated with a jack connector in
the switchboard. The operator observed all incoming calls, identified
the phone sets for which they were intended, and then used
wires to connect the appropriate jacks. At the end of the call, the
jacks were disconnected.
This cumbersome methodology limited the size and efficiency of
telephone networks and invaded the privacy of callers. The development
of automated switching systems soon solved these problems
and made switchboard operators obsolete. It was here that
Antoine Barnay’s rotary dial was used, making possible an exchange
that automatically linked the phone sets of callers and call
recipients in the following way.
First, a caller lifted a telephone “off the hook,” causing a switchhook,
like those used in modern phones, to close the circuit that connected
the telephone set to the telephone network. Immediately, a
dial tone (still familiar to callers) came on to indicate that the automatic
switching system could handle the planned call. When the
phone dial was used, each number or letter that was dialed produced
a fixed number of clicks. Every click indicated that an electrical
pulse had been sent to the network’s automatic switching system,
causing switches to change position slightly. Immediately after
a complete telephone number was dialed, the overall operation of
the automatic switchers connected the two telephone sets. This connection
was carried out much more quickly and accurately than had
been possible when telephone operators at manual switchboards
made the connection.
The telephone has become the world’s most important communication
device. Most adults use it between six and eight times per
day, for personal and business calls. This widespread use has developed
because huge changes have occurred in telephones and telephone
networks. For example, automatic switching and the rotary
dial system were only the beginning of changes in phone calling.
Touch-tone dialing replaced Barnay’s electrical pulses with audio
tones outside the frequency of human speech. This much-improved
system can be used to send calls over much longer distances than
was possible with the rotary dial system, and it also interacts well
with both answering machines and computers.
Another advance in modern telephoning is the use of radio
transmission techniques in mobile phones, rendering telephone
cords obsolete. The mobile phone communicates with base stations
arranged in “cells” throughout the service area covered. As the user
changes location, the phone link automatically moves from cell to
cell in a cellular network.
In addition, the use of microwave, laser, and fiber-optic technologies
has helped to lengthen the distance over which phone calls can
be transmitted. These technologies have also increased the number
of messages that phone networks can handle simultaneously and
have made it possible to send radio and television programs (such
as cable television), scientific data (via modems), and written messages
(via facsimile, or “fax,” machines) over phone lines. Many
other advances in telephone technology are expected as society’s
needs change and new technology is developed.
Alexander Graham Bell
During the funeral for Alexander Graham Bell in 1922, telephone
service throughout the United States stopped for one
minute to honor him. To most people he was the inventor of the
telephone. In fact, his genius ranged much further.
Bell was born in Edinburgh, Scotland, in 1847. His father,
an elocutionist who invented a phonetic alphabet, and his
mother, who was deaf, imbued him with deep curiosity, especially
about sound. As a boy Bell became an exceptional pianist,
and he produced his first invention, for cleaning wheat, at
fourteen. After Edinburgh’s Royal High School, he attended
classes at Edinburgh University and University College, London,
but at the age of twenty-three, battling tuberculosis, he
left school to move with his parents to Ontario, Canada, to
convalesce. Meanwhile, he worked on his idea for a telegraph
capable of sending multiple messages at once. From it grew
the basic concept for the telephone. He developed it while
teaching Visible Speech at the Boston School for Deaf Mutes
after 1871. Assisted by ThomasWatson, he succeeded in sending
speech over a wire and was issued a patent for his device,
among the most valuable ever granted, in 1876. His demonstration
of the telephone later that year at Philadelphia’s
Centennial Exhibition and its subsequent development into a
household appliance brought him wealth and fame.
He moved to Nova Scotia, Canada, and continued inventing.
He created a photophone, tetrahedron modules for construction,
and an airplane, the Silver Dart, which flew in 1909.
Even though existing technology made them impracticable,
some of his ideas anticipated computers and magnetic sound
recording. His last patented invention, tested three years before
his death, was a hydrofoil. Capable of reaching seventy-one
miles per hour and freighting fourteen thousand pounds, the
HD-4 was then the fastest watercraft in the world.
Bell also helped found the National Geographic Society in
1888 and became its president in 1898. He hired Gilbert Grosvenor
to edit the society’s famous magazine, National Geographic
and together they planned the format—breathtaking
photography and vivid writing—that made it one of the world’s
best known magazines.
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