Rotary dial telephone (Inventions)

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.
Rotary-dial telephone. (Image Club Graphics)
Rotary-dial telephone. (Image Club Graphics)

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

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 Thomas Watson, 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 Gros-venor 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.
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 switch-hook, 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.
See also Cell phone; Internet; Long-distance telephone; Telephone switching; Touch-tone telephone.

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