17 August 2009

Long-distance telephone

The invention: System for conveying voice signals via wires over long distances. The people behind the invention: Alexander Graham Bell (1847-1922), a Scottish American inventor Thomas A. Watson (1854-1934), an American electrical engineer The Problem of Distance The telephone may be the most important invention of the nineteenth century. The device developed by Alexander Graham Bell and Thomas A. Watson opened a new era in communication and made it possible for people to converse over long distances for the first time. During the last two decades of the nineteenth century and the first decade of the twentieth century, the American Telephone and Telegraph (AT&T) Company continued to refine and upgrade telephone facilities, introducing such innovations as automatic dialing and long-distance service. One of the greatest challenges faced by Bell engineers was to develop a way of maintaining signal quality over long distances. Telephone wires were susceptible to interference from electrical storms and other natural phenomena, and electrical resistance and radiation caused a fairly rapid drop-off in signal strength, which made long-distance conversations barely audible or unintelligible. By 1900, Bell engineers had discovered that signal strength could be improved somewhat by wrapping the main wire conductor with thinner wires called “loading coils” at prescribed intervals along the length of the cable. Using this procedure, Bell extended longdistance service from New York to Denver, Colorado, which was then considered the farthest point that could be reached with acceptable quality. The result, however, was still unsatisfactory, and Bell engineers realized that some form of signal amplification would be necessary to improve the quality of the signal.A breakthrough came in 1906, when Lee de Forest invented the “audion tube,” which could send and amplify radio waves. Bell scientists immediately recognized the potential of the new device for long-distance telephony and began building amplifiers that would be placed strategically along the long-distance wire network. Work progressed so quickly that by 1909, Bell officials were predicting that the first transcontinental long-distance telephone service, between New York and San Francisco, was imminent. In that year, Bell president Theodore N. Vail went so far as to promise the organizers of the Panama-Pacific Exposition, scheduled to open in San Francisco in 1914, that Bell would offer a demonstration at the exposition. The promise was risky, because certain technical problems associated with sending a telephone signal over a 4,800- kilometer wire had not yet been solved. De Forest’s audion tube was a crude device, but progress was being made. Two more breakthroughs came in 1912, when de Forest improved on his original concept and Bell engineer Harold D. Arnold improved it further. Bell bought the rights to de Forest’s vacuumtube patents in 1913 and completed the construction of the New York-San Francisco circuit. The last connection was made at the Utah-Nevada border on June 17, 1914. Success Leads to Further Improvements Bell’s long-distance network was tested successfully on June 29, 1914, but the official demonstration was postponed until January 25, 1915, to accommodate the Panama-Pacific Exposition, which had also been postponed. On that date, a connection was established between Jekyll Island, Georgia, where Theodore Vail was recuperating from an illness, and New York City, where Alexander Graham Bell was standing by to talk to his former associate Thomas Watson, who was in San Francisco. When everything was in place, the following conversation took place. Bell: “Hoy! Hoy! Mr. Watson? Are you there? Do you hear me?”Watson: “Yes, Dr. Bell, I hear you perfectly. Do you hear me well?” Bell: “Yes, your voice is perfectly distinct. It is as clear as if you were here in New York.” The first transcontinental telephone conversation transmitted by wire was followed quickly by another that was transmitted via radio. Although the Bell company was slow to recognize the potential of radio wave amplification for the “wireless” transmission of telephone conversations, by 1909 the company had made a significant commitment to conduct research in radio telephony. On April 4, 1915, a wireless signal was transmitted by Bell technicians from Montauk Point on Long Island, New York, to Wilmington, Delaware, a distance of more than 320 kilometers. Shortly thereafter, a similar test was conducted between New York City and Brunswick, Georgia, via a relay station at Montauk Point. The total distance of the transmission was more than 1,600 kilometers. Finally, in September, 1915, Vail placed a successful transcontinental radiotelephone call from his office in New York to Bell engineering chief J. J. Carty in San Francisco. Only a month later, the first telephone transmission across the Atlantic Ocean was accomplished via radio from Arlington, Virginia, to the Eiffel Tower in Paris, France. The signal was detectable, although its quality was poor. It would be ten years before true transatlantic radio-telephone service would begin. The Bell company recognized that creating a nationwide longdistance network would increase the volume of telephone calls simply by increasing the number of destinations that could be reached from any single telephone station. As the network expanded, each subscriber would have more reason to use the telephone more often, thereby increasing Bell’s revenues. Thus, the company’s strategy became one of tying local and regional networks together to create one large system. Impact Just as the railroads had interconnected centers of commerce, industry, and agriculture all across the continental United States in the nineteenth century, the telephone promised to bring a new kind of interconnection to the country in the twentieth century: instantaneous voice communication. During the first quarter century after the invention of the telephone and during its subsequent commercialization, the emphasis of telephone companies was to set up central office switches that would provide interconnections among subscribers within a fairly limited geographical area. Large cities were wired quickly, and by the beginning of the twentieth century most were served by telephone switches that could accommodate thousands of subscribers. The development of intercontinental telephone service was a milestone in the history of telephony for two reasons. First, it was a practical demonstration of the almost limitless applications of this innovative technology. Second, for the first time in its brief history, the telephone network took on a national character. It became clear that large central office networks, even in large cities such as New York, Chicago, and Baltimore, were merely small parts of a much larger, universally accessible communication network that spanned a continent. The next step would be to look abroad, to Europe and beyond.


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