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.

Long-distance radiotelephony

The invention: The first radio transmissions fromthe United States to Europe opened a new era in telecommunications. The people behind the invention: Guglielmo Marconi (1874-1937), Italian inventor of transatlantic telegraphy Reginald Aubrey Fessenden (1866-1932), an American radio engineer Lee de Forest (1873-1961), an American inventor Harold D. Arnold (1883-1933), an American physicist John J. Carty (1861-1932), an American electrical engineer An Accidental Broadcast The idea of commercial transatlantic communication was first conceived by Italian physicist and inventor Guglielmo Marconi, the pioneer of wireless telegraphy. Marconi used a spark transmitter to generate radio waves that were interrupted, or modulated, to form the dots and dashes of Morse code. The rapid generation of sparks created an electromagnetic disturbance that sent radio waves of different frequencies into the air—a broad, noisy transmission that was difficult to tune and detect. The inventor Reginald Aubrey Fessenden produced an alternative method that became the basis of radio technology in the twentieth century. His continuous radio waves kept to one frequency, making them much easier to detect at long distances. Furthermore, the continuous waves could be modulated by an audio signal, making it possible to transmit the sound of speech. Fessenden used an alternator to generate electromagnetic waves at the high frequencies required in radio transmission. It was specially constructed at the laboratories of the General Electric Company. The machine was shipped to Brant Rock, Massachusetts, in 1906 for testing. Radio messages were sent to a boat cruising offshore, and the feasibility of radiotelephony was thus demonstrated. Fessenden followed this success with a broadcast of messages and music between Brant Rock and a receiving station constructed at Plymouth, Massachusetts. The equipment installed at Brant Rock had a range of about 160 kilometers. The transmission distance was determined by the strength of the electric power delivered by the alternator, which was measured in watts. Fessenden’s alternator was rated at 500 watts, but it usually delivered much less power. Yet this was sufficient to send a radio message across the Atlantic. Fessenden had built a receiving station at Machrihanish, Scotland, to test the operation of a large rotary spark transmitter that he had constructed. An operator at this station picked up the voice of an engineer at Brant Rock who was sending instructions to Plymouth. Thus, the first radiotelephone message had been sent across the Atlantic by accident. Fessenden, however, decided not to make this startling development public. The station at Machrihanish was destroyed in a storm, making it impossible to carry out further tests. The successful transmission undoubtedly had been the result of exceptionally clear atmospheric conditions that might never again favor the inventor. One of the parties following the development of the experiments in radio telephony was the American Telephone and Telegraph (AT&T) Company. Fessenden entered into negotiations to sell his system to the telephone company, but, because of the financial panic of 1907, the sale was never made. Virginia to Paris and Hawaii The English physicist John Ambrose Fleming had invented a twoelement (diode) vacuum tube in 1904 that could be used to generate and detect radio waves. Two years later, the American inventor Lee de Forest added a third element to the diode to produce his “audion” (triode), which was a more sensitive detector. John J. Carty, head of a research and development effort at AT&T, examined these new devices carefully. He became convinced that an electronic amplifier, incorporating the triode into its design, could be used to increase the strength of telephone signals and to long distances. On Carty’s advice, AT&T purchased the rights to de Forest’s audion. A team of about twenty-five researchers, under the leadership of physicist Harold D. Arnold, were assigned the job of perfecting the triode and turning it into a reliable amplifier. The improved triode was responsible for the success of transcontinental cable telephone service, which was introduced in January, 1915. The triode was also the basis of AT&T’s foray into radio telephony. Carty’s research plan called for a system with three components: an oscillator to generate the radio waves, a modulator to add the audio signals to the waves, and an amplifier to transmit the radio waves. The total power output of the system was 7,500 watts, enough to send the radio waves over thousands of kilometers.The apparatus was installed in the U.S. Navy’s radio tower in Arlington, Virginia, in 1915. Radio messages from Arlington were picked up at a receiving station in California, a distance of 4,000 kilometers, then at a station in Pearl Harbor, Hawaii, which was 7,200 kilometers from Arlington. AT&T’s engineers had succeeded in joining the company telephone lines with the radio transmitter at Arlington; therefore, the president of AT&T, Theodore Vail, could pick up his telephone and talk directly with someone in California. The next experiment was to send a radio message fromArlington to a receiving station set up in the Eiffel Tower in Paris. After several unsuccessful attempts, the telephone engineers in the Eiffel Tower finally heard Arlington’s messages on October 21, 1915. The AT&T receiving station in Hawaii also picked up the messages. The two receiving stations had to send their reply by telegraph to the United States because both stations were set up to receive only. Two-way radio communication was still years in the future. Impact The announcement that messages had been received in Paris was front-page news and brought about an outburst of national pride in the United States. The demonstration of transatlantic radio telephony was more important as publicity for AT&T than as a scientific advance. All the credit went to AT&T and to Carty’s laboratory. Both Fessenden and de Forest attempted to draw attention to their contributions to long-distance radio telephony, but to no avail. The Arlington-to-Paris transmission was a triumph for corporate public relations and corporate research. The development of the triode had been achieved with large teams of highly trained scientists—in contrast to the small-scale efforts of Fessenden and de Forest, who had little formal scientific training. Carty’s laboratory was an example of the new type of industrial research that was to dominate the twentieth century. The golden days of the lone inventor, in the mold of Thomas Edison or Alexander Graham Bell, were gone. In the years that followed the first transatlantic radio telephone messages, little was done by AT&T to advance the technology or to develop a commercial service. The equipment used in the 1915 demonstration was more a makeshift laboratory apparatus than a prototype for a new radio technology. The messages sent were short and faint. There was a great gulf between hearing “hello” and “goodbye” amid the static. The many predictions of a direct telephone connection between New York and other major cities overseas were premature. It was not until 1927 that a transatlantic radio circuit was opened for public use. By that time, a new technological direction had been taken, and the method used in 1915 had been superseded by shortwave radio communication.

Laser vaporization

The invention: Technique using laser light beams to vaporize the plaque that clogs arteries. The people behind the invention: Albert Einstein (1879-1955), a theoretical American physicist Theodore Harold Maiman (1927- ), inventor of the laser Light, Lasers, and Coronary Arteries Visible light, a type of electromagnetic radiation, is actually a form of energy. The fact that the light beams produced by a light bulb can warm an object demonstrates that this is the case. Light beams are radiated in all directions by a light bulb. In contrast, the device called the “laser” produces light that travels in the form of a “coherent” unidirectional beam. Coherent light beams can be focused on very small areas, generating sufficient heat to melt steel. The term “laser” was invented in 1957 by R. Gordon Gould of Columbia University. It stands for light amplification by stimulated emission of radiation, the means by which laser light beams are made. Many different materials—including solid ruby gemstones, liquid dye solutions, and mixtures of gases—can produce such beams in a process called “lasing.” The different types of lasers yield light beams of different colors that have many uses in science, industry, and medicine. For example, ruby lasers, which were developed in 1960, are widely used in eye surgery. In 1983, a group of physicians in Toulouse, France, used a laser for cardiovascular treatment. They used the laser to vaporize the “atheroma” material that clogs the arteries in the condition called “atherosclerosis.” The technique that they used is known as “laser vaporization surgery.” Laser Operation, Welding, and Surgery Lasers are electronic devices that emit intense beams of light when a process called “stimulated emission” occurs. The principles of laser operation, including stimulated emission, were established by Albert Einstein and other scientists in the first third of the twentieth century. In 1960, Theodore H. Maiman of the Hughes Research Center in Malibu, California, built the first laser, using a ruby crystal to produce a laser beam composed of red light. All lasers are made up of three main components. The first of these, the laser’s “active medium,” is a solid (like Maiman’s ruby crystal), a liquid, or a gas that can be made to lase. The second component is a flash lamp or some other light energy source that puts light into the active medium. The third component is a pair of mirrors that are situated on both sides of the active medium and are designed in such a way that one mirror transmits part of the energy that strikes it, yielding the light beam that leaves the laser. Lasers can produce energy because light is one of many forms of energy that are called, collectively, electromagnetic radiation (among the other forms of electromagnetic radiation are X rays and radio waves). These forms of electromagnetic radiation have different wavelengths; the smaller the wavelength, the higher the energy level. The energy level is measured in units called “quanta.” The emission of light quanta from atoms that are said to be in the “excited state” produces energy, and the absorption of quanta by unexcited atoms— atoms said to be in the “ground state”—excites those atoms. The familiar light bulb spontaneously and haphazardly emits light of many wavelengths from excited atoms. This emission occurs in all directions and at widely varying times. In contrast, the light reflection between the mirrors at the ends of a laser causes all of the many excited atoms present in the active medium simultaneously to emit light waves of the same wavelength. This process is called “stimulated emission.” Stimulated emission ultimately causes a laser to yield a beam of coherent light, which means that the wavelength, emission time, and direction of all the waves in the laser beam are the same. The use of focusing devices makes it possible to convert an emitted laser beam into a point source that can be as small as a few thousandths of an inch in diameter. Such focused beams are very hot, and they can be used for such diverse functions as cutting or welding metal objects and performing delicate surgery. The nature of the active medium used in a laser determines the wavelength of its emitted light beam; this in turn dictates both the energy of the emitted quanta and the appropriate uses for the laser.Maiman’s ruby laser, for example, has been used since the 1960’s in eye surgery to reattach detached retinas. This is done by focusing the laser on the tiny retinal tear that causes a retina to become detached. The very hot, high-intensity light beam then “welds” the retina back into place, bloodlessly, by burning it to produce scar tissue. The burning process has no effect on nearby tissues. Other types of lasers have been used in surgeries on the digestive tract and the uterus since the 1970’s. In 1983, a group of physicians began using lasers to treat cardiovascular disease. The original work, which was carried out by a number of physicians in Toulouse, France, involved the vaporization of atheroma deposits (atherosclerotic plaque) in a human artery. This very exciting event added a new method to medical science’s arsenal of life-saving techniques. Consequences Since their discovery, lasers have been used for many purposes in science and industry. Such uses include the study of the laws of chemistry and physics, photography, communications, and surveying. Lasers have been utilized in surgery since the mid-1960’s, and their use has had a tremendous impact on medicine. The first type of laser surgery to be conducted was the repair of detached retinas via ruby lasers. This technique has become the method of choice for such eye surgery because it takes only minutes to perform rather than the hours required for conventional surgical methods. It is also beneficial because the lasing of the surgical site cauterizes that site, preventing bleeding. In the late 1970’s, the use of other lasers for abdominal cancer surgery and uterine surgery began and flourished. In these forms of surgery, more powerful lasers are used. In the 1980’s, laser vaporization surgery (LVS) began to be used to clear atherosclerotic plaque (atheromas) from clogged arteries. This methodology gives cardiologists a useful new tool. Before LVS was available, surgeons dislodged atheromas by means of “transluminal angioplasty,” which involved pushing small, fluoroscopeguided inflatable balloons through clogged arteries.