Rotary dial telephone

The invention:



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

speaker’s voice.

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.





 Impact



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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