TELEKOMUNIKACJA

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TELEKOMUNIKACJA

• NOWA DZIEDZINA NAUKI

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telegraph
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The first permanently successful telegraphic
cable crossing the Atlantic Ocean was laid in
1866. In 1872, J. B. Stearns of Massachusetts
devised a method for duplex telegraphy,
enabling two messages to be sent over the same
wire at the same time. In 1874, Thomas A. Edison
invented the quadruplex method for the
simultaneous transmission of four messages over
the same wire. In addition to wires and cables,
telegraph messages are now sent by such means as
radio waves, microwaves, and communications
satellites (see satellite, artificial ). Today
telegraphy is less widely used, having been
supplanted by the telephone , facsimile machines,
and computer electronic mail
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telephone   
device for communicating sound, especially
speech, usually by means of wires in an electric
circuit. The telephones now in general use
evolved from the device invented by Alexander
Graham Bell and patented by him in 1876 and 1877.
Although Bell is recognized as the inventor, his
telephone was preceded by many attempts to
produce such an instrument. The principles on
which it is based, and effective model
instruments, were developed by different men at
so nearly the same time that there are disputes
about priority. In Bell's instrument, an electric
current varied in intensity and frequency in
accordance with sound waves. The sound waves
caused a thin plate of soft iron, called the
diaphragm, to vibrate. The vibrations disturbed
the magnetic field of a bar magnet placed near
the diaphragm, and this disturbance induced an
electric current in a wire wound about the
magnet. That current, when transmitted to a
distant identical instrument, caused the
diaphragm in it to vibrate, reproducing the
original sound. Bell's instrument was thus both
transmitter and receiver. The first notable
improvement of the Bell telephone differentiated
the transmitting instrument from the receiving
instrument. Many other inventions have improved
the telephone.     The switches used to route
telephone calls, which were once
electromechanical, are now largely replaced by
sophisticated digital electronic switching
systems. The electronic switches are much more
flexible because they can be programmed to
provide new services. The latest generation of
switches have made a number of new features
possible. Users, for example, can read the
telephone number of the calling party on a
display device if they choose to subscribe to a
caller ID service. In call waiting, audio
signals let a person already on a telephone know
that someone else is trying to reach that person.
Subscribers can also program the telephone
switches to forward their calls automatically to
another number ( call forwarding ). Other
features include voice mailboxes and the ability
to make three-way conference calls.
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The problems associated with long-distance and
intercity telephone service have been met with
increasing success. The telephone lines used
include the ordinary open wire lines,
lead-sheathed cables consisting of many lines,
and coaxial and fiber-optic cables. Coaxial and
fiber-optic cables are typically placed
underground, but other cables may be either
overhead or underground. Transmission of
telephone messages over long distances is often
accomplished by means of radio and microwave
transmissions. In some cases microwaves are sent
to an orbiting communications satellite (see
satellite, artificial ) from which they are
relayed back to a distant point on the earth.
Cellular telephone systems allow small, low-power
portable transceivers access to the telephone
network some cellular models provide access to
the Internet.     With the advent of the
Internet , computer programs have been developed
that allow voice communications across long
distances, bypassing conventional carriers. The
programs and plays the sound almost
instantaneously. The advantage of using the
Internet is that under current tariffs no
long-distance charges accrue, regardless of the
length of the conversation. The disadvantages are
the relatively inferior sound quality, the need
for both computers to be running the same
program, and the difficulty of establishing the
connection between the computers. , which
require a computer equipped with a modem ,
microphone, and speakers, compress the voice
message into digital signals. These are
transmitted over the phone line to another
computer, which must have another copy of the
same program. The second program decompresses the
digital signals
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In 1984 a federal court ordered American
Telephone and Telegraph Company (ATT) to divest
its Bell Telephone operating companies (the Baby
Bells ) after the court ruled that ATT held a
monopoly over U.S. telephone service. Since then,
the regional operating companies and new
competitors for long-distance service have grown
through acquisitions and mergers. By the end of
the 1990s, ATT remained the largest U.S.
long-distance provider, followed by WorldCom
(comprising MCI, Sprint, and WorldCom). At the
start of the 21st cent., the distinctions between
types of telephone providers began to blur, as
long-distance carriers (such as MCI) started to
offer local phone service and local/regional
phone companies (such as Bell Atlantic, now
Verizon) began to provide long-distance service.
Telephone companies have explored partnerships
with media conglomerates for integrating access
to cable television , fiber optics , and the
Internet.     The primary regulator of
telephone service in the United States is the
Federal Communications Commission . The
International Telecommunication Union coordinates
aspects of international transmissions.
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Bell, Alexander Graham   
1847-1922, American scientist, inventor of the
telephone, b. Edinburgh, Scotland, educated at
the Univ. of Edinburgh and University College,
London son of Alexander Melville Bell. He worked
in London with his father, whose system of
visible speech he used in teaching the deaf to
talk. In 1870 he went to Canada, and in 1871 he
lectured, chiefly to teachers of the deaf, in
Boston and other cities. During the next few
years he conducted his own school of vocal
physiology in Boston, lectured at Boston Univ.,
and worked on his inventions. His teaching
methods were of lasting value in the improvement
of education for the deaf. As early as 1865, Bell
conceived the idea of transmitting speech by
electric waves. In 1875, while he was
experimenting with a multiple harmonic telegraph,
the principle of transmission and reproduction
came to him. By Mar. 10, 1876, his apparatus was
so far developed that the first complete sentence
transmitted, Watson, come here I want you, was
distinctly heard by his assistant. The first
demonstration took place before the American
Academy of Arts and Sciences in Boston on May 10,
1876, and a more significant one, at the
Philadelphia Centennial Exposition the same year,
introduced the telephone to the world. The Bell
Telephone Company was organized in July, 1877. A
long period of patent litigation followed in
which Bell's claims were completely upheld by the
U.S. Supreme Court. With the 50,000 francs
awarded him as the Volta Prize for his invention,
he established in Washington, D.C., the Volta
Laboratory, where the first successful sound
recorder, the Graph phone, was produced. Bell
invented the photo phone, which transmitted
speech by light rays the audiometer, another
invention for the deaf the induction balance,
used to locate metallic objects in the human
body and the flat and the cylindrical wax
recorders for phonographs. He investigated the
nature and causes of deafness and made an
elaborate study of its heredity. The magazine
Science, which became the official organ for the
American Association for the Advancement of
Science, was founded (1880) largely through his
influence. He was president of the National
Geographic Society from 1898 to 1903 and was made
a regent of the Smithsonian Institution in 1898.
After 1895 his interest was occupied largely by
aviation. He invented the tetrahedral kite. The
Aerial Experiment Association, founded under his
patronage in 1907, brought together G. H. Curtis,
F. W. Baldwin, and others, who invented the
aileron principle and developed the hydroplane
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Morse, Samuel Finley Breese   
1791-1872, American inventor and artist, b.
Charlestown, Mass., grad. Yale, 1810. He studied
painting in England under Washington Allston and
achieved some success. He returned to the United
States in 1815, took up portrait painting, and
gained a considerable reputation in this field.
He was a founder (1825) of the National Academy
of Design. He spent the years from 1829 to 1832
in further European study. His interest in
electricity, aroused in his college days, was
further stimulated by the lectures of James F.
Dana in 1827 and later by contacts with members
of the faculty of New York Univ. Learning in 1832
of Ampere's idea for the electric telegraph,
Morse worked for the next 12 years, with the aid
of Leonard Gale, Joseph Henry, and Alfred Vail,
to perfect his own version of the instrument. So
many phases of the telegraph, however, had
already been anticipated by other inventors,
especially in Great Britain, Germany, and France,
that Morse's originality as the inventor of
telegraphy has been questioned even the Morse
code did not differ greatly from earlier codes,
including the semaphore. In any case, Morse in
1844 demonstrated to Congress the practicability
of his instrument by transmitting the famous
message What hath God wrought over a wire from
Washington to Baltimore. Morse subsequently was
compelled to defend his invention in court,
although by then he commanded the acclaim of the
world. He later experimented with submarine cable
telegraphy. Both Morse and John Draper were
instrumental in introducing the daguerreotype in
the United States
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