Telephone

Electrical telecommunication originated in the nineteenth century, with the invention of the tele graph—a method of transferring intelligence between distant places through metallic wires in a form of spaced bursts of electricity. A sender, using a special letter code, produced regulated electrical pulses in a circuit. These signals were converted at the receiving end into a pattern of sound clicks, which was decoded by an operator or an automatic device. The next logical step beyond sending of non-articulate messages was the instantaneous transmission of conversation over wires. The intricate and very individual nature of sounds produced by the human vocal cords with the participation of the lips, as well as of the oral and nasal cavities, made this task difficult to accomplish. Articulate (spoken) speech involves not only the elementary sounds and their assembly into syllables, words, and sentences, but also infinite variations in accent, emphasis, intonation, and voice timbre—characteristics of no importance for other types communication.

By no chance, the invention of a way to transmit the human voice electrically was made by a man deeply involved in the study of vocal physiology and the mechanics of speech. A native of Scotland, Alexander Graham Bell (1847-1922) inherited from his father, who was a Figure 2. Telephone network. Illustration by Hans & Cassidy. Courtesy of Gale Group. famous professor of elocution and an author of several textbooks on speech correction, a profound interest in speech and hearing theory, and put his knowledge primarily for the teaching of the deaf. Being interested in electricity, Bell set up a little laboratory and experimented on transmission of sound tones over an electric circuit in an attempt to make a "harmonic telegraph"—a device capable of sending multiple telegraph messages simultaneously over the same wire. On the basis of his experimental observations, Bell gradually came to the conclusion that oscillations of air pressure (sound waves) could be used to modulate the intensity of electric current in a circuit. Using his knowledge of ear anatomy, Bell attached one end of a metallic organ reed to a thin diaphragm intended to simulate the eardrum. In presence of even weak air-pressure variations caused by the human voice, the diaphragm forced the metallic reed to oscillate in front of the electromagnet and, therefore, to undulate the electric current in the circuit.

Telephones successfully served to the public for almost 23 years before scientists could explain theoretically why the telephone worked. Bell's perception of an "analog" relationship between sound pressure and electromotive force was one of the most fascinating examples of the ingenious intuition in the history of technological discoveries.

Bell first started testing his device for voice transmission in June, 1875, and patented it nine months later. The demonstration of the working apparatus at the Philadelphia Centennial Exposition attracted substantial public interest, which helped to raise some additional monetary funds. On 1 August 1877, with Bell's four patents as a tangible basis for a wide manufacturing of a speaking telephone, the Bell Telephone Company was formed. Bell outlined a general concept of a telephone system as a universal means of voice communication between individuals, at any time, from any location, and without any special skill requirements. This concept might seem obvious today, but it was far in advance of any existing techniques of its time. Giant technological and organizational efforts were required to make Bell's vision of a telephone communication a reality.

The number of existing telephones at that time counted 778, but rapidly growing demand presented the challenge of operating the existing telephone while producing new ones. The first telephone subscribers were directly connected to each other. Under such arrangement, a community of 100 subscribers used 9,900 separate wire connections. For 1,000 subscribers the number of needed wire connections was more than 100 times bigger. The evident impracticality of full-time point-to-point connections stimulated the idea of a central office, or exchange. All the telephone sets in a particular area, instead of being wired permanently to each other, were connected to the same central office, which could establish a temporary link between any two of them on demand. The process of line connecting and disconnecting (switching) was initially performed by trained operators on a switchboard. However, with more and more telephones coming into use the manual switching was becoming increasingly complex. In 1891, the first automatic switching system was introduced.

Figure 3. Cellular network. Illustration by Hans & Cassidy. Courtesy of Gale Group.

As local telephone lines emerged and expanded, the idea of the creation and commercial operation of long-distance telephone communication became a necessity. Unfortunately, the already existing telegraph lines were of little use for this purpose. Feeble electric currents used in telephony were rapidly dissipated (attenuated) on their way through iron wires. Compensating for attenuation was one of the main problems of telephony during its first 50 years. Considerable success in reducing the attenuation was achieved by using copper in place of iron wire. The innovation extended the limits of the voice transmission through bare wires to a distance between Boston and Chicago—1180 mi (1,900 km)—in 1893. Later, the effectiveness of wire lines was crucially increased by inserting inductances, or "loading coils," at regular distances in a circuit. For crossing small bodies of water telephone lines were laid in a form of insulated cables instead of bare wires. The invention of radio transmission at the beginning of the twentieth century led to the development of wireless telephone links and accelerated creation of the worldwide telephone system.

Long-haul facilities grew swiftly. In 1900, toll lines totalled 621,000 mi (1 million km) of wire. It took only 25 years to increase this number by a factor of 10. In 1925, almost one-half of the long-distance circuits was cable. The first transatlantic telephone cable (TAT-1) became operational in 1956. Nine years later, the first transatlantic telephone satellite "Earlybird" went into service.