| | - Atlantic languages
- branch of the Niger-Congo language family spoken primarily in Senegal, The Gambia, Guinea, Guinea-Bissau, Sierra Leone, and Liberia. The approximately 45 Atlantic languages are spoken by about 30 million people. One language cluster, Fula (also called Fulani, Peul, Fulfulde, and Toucouleur), accounts for more than half of this number and ...
- Atlantic Monthly, The
- American monthly journal of literature and opinion, published in Boston. One of the oldest and most respected of American reviews, The Atlantic Monthly was founded in 1857 by Moses Dresser Phillips and Francis H. Underwood. It has long been noted for the quality of its fiction and general articles, contributed ...
- Atlantic Ocean
- body of salt water covering approximately one-fifth of the Earth's surface and separating the continents of Europe and Africa to the east from those of North and South America to the west. The ocean's name, derived from Greek mythology, means the "Sea of Atlas." It is second in size only ...
- Atlantic Records
- Formed in 1947 by jazz fans Ahmet Ertegun, son of a Turkish diplomat, and Herb Abramson, formerly the artists-and-repertoire director for National Records, Atlantic became the most consistently successful New York City-based independent label of the 1950s, with an incomparable roster including Joe Turner, Ruth Brown, the Clovers, Ray Charles, ...
- Atlantic Richfield Company
- former American petroleum corporation that was headquartered in Los Angeles and was bought in 2000 by the giant BP Amoco (later BP PLC).
- Atlantic salmon
- (species Salmo salar), oceanic trout of the family Salmonidae, a highly prized game fish. It averages about 5.5 kg (12 pounds) and is marked with round or cross-shaped spots. Found on both sides of the Atlantic Ocean, it enters streams in the fall to spawn. After spawning, adults are called ...
- Atlantic, Battle of the
- in World War II, a contest between the Western Allies and the Axis powers (particularly Germany) for the control of Atlantic sea routes. For the Allied powers, the battle had three objectives: blockade of the Axis powers in Europe, security of Allied sea movements, and freedom to project military power ...
- Atlantico
- departamento, northwestern Colombia, located on the Caribbean coastal plain and bounded east by the Magdalena River. The department was established in 1905. Although it is one of Colombia's smallest departments, Atlantico's position at the mouth of one of the continent's major rivers is of strategic importance. Almost three-fourths of the ...
- Atlantis
- a legendary island in the Atlantic Ocean, lying west of the Straits of Gibraltar. The principal sources for the legend are two of Plato's dialogues, Timaeus and Critias. In the former, Plato describes how Egyptian priests, in conversation with the Athenian lawgiver Solon, described Atlantis as an island larger than ...
- Atlantis II Deep
- submarine basin, the largest in the Red Sea, located at latitude 2123' N and longitude 3804' E. The Atlantis II Deep attains a maximum depth of 7,160 feet (2,170 metres)
- Atlas
- in Greek mythology, son of the Titan Iapetus and the Oceanid Clymene (or Asia) and brother of Prometheus (creator of humankind). In Homer's Odyssey, Book I, Atlas seems to have been a marine creature who supported the pillars that held heaven and earth apart. These were thought to rest in ...
- Atlas
- series of American launch vehicles, designed originally as intercontinental ballistic missiles (ICBMs), that have been in service since the late 1950s.
- atlas
- in architecture, male figure used as a column to support an entablature, balcony, or other projection, originating in the Classical architecture of antiquity. Such figures are posed as if supporting great weights (e.g., Atlas bearing the world). The related telamon of Roman architecture, the male counterpart of the caryatid (q.v.), ...
- atlas
- a collection of maps or charts, usually bound together. The name derives from a custom-initiated by Gerardus Mercator in the 16th century-of using the figure of the Titan Atlas, holding the globe on his shoulders, as a frontispiece for books of maps. In addition to maps and charts, atlases often ...
- Atlas Mountains
- series of mountain ranges in northwestern Africa, running generally southwest to northeast to form the geologic backbone of the countries of the Maghrib (the western region of the Arab world)-Morocco, Algeria, and Tunisia. They extend for more than 1,200 miles (2,000 kilometres), from the Moroccan port of Agadir in the ...
- Atlas Shrugged
- novel by Ayn Rand, published in 1957. The book's female protagonist, Dagny Taggart, struggles to manage a transcontinental railroad amid the pressures and restrictions of massive bureaucracy. Her antagonistic reaction to a libertarian group seeking an end to government regulation is later echoed and modified in her encounter with a ...
- Atlas, Charles
- Italian-born American bodybuilder and physical culturist who, with Frederick Tilney and Charles P. Roman, created and marketed a highly popular mail-order bodybuilding course.
- Atli, Lay of
- heroic poem in the Norse Poetic Edda (see Edda), an older variant of the tale of slaughter and revenge that is the subject of the German epic Nibelungenlied, from which it differs in several respects. In the Norse poem, Atli (the Hunnish king Attila) is the villain, who is slain ...
- Atlixco
- city, southwestern Puebla estado (state), south-central Mexico. It lies at 6,171 feet (1,881 metres) above sea level in a fertile valley irrigated by the Molinos River, which descends from the southeastern slopes of Iztaccihuatl volcano. Founded in 1579 as Villa de Carrion, after its founder, Alonso Diaz de Carrion, Atlixco ...
- atman
- one of the most basic concepts in Hinduism, the universal self, identical with the eternal core of the personality that after death either transmigrates to a new life or attains release (moksha) from the bonds of existence. While in the early Vedas it occurred mostly as a reflexive pronoun meaning ...
- Atmaramji
- , important Jain reformer and revivalist monk. He was born a Hindu but as a child came under the influence of Sthanakavasi Jain monks and was initiated as a Sthanakavasi monk in 1854. He was renowned for his prodigious memory and intellectual skills. He pursued an independent study of Jain ...
- Atmore
- city, Escambia county, southwestern Alabama, U.S. It lies just north of the Florida state line, about 50 miles (80 km) northeast of Mobile. The city was founded in 1866 by William Larkin Williams, who established a railroad supply stop that became known as Williams Station. Settlers were attracted by the ...
- atmosphere
- the gas and aerosol envelope that extends from the ocean, land, and ice-covered surface of a planet outward into space. The density of the atmosphere decreases outward, because the gravitational attraction of the planet, which pulls the gases and aerosols (microscopic suspended particles of dust, soot, smoke, or chemicals) inward, ...
- atmosphere, evolution of
- the development of Earth's atmosphere across geologic time. The process by which the current atmosphere arose from earlier conditions is complex; however, evidence related to the evolution of Earth's atmosphere, though indirect, is abundant. Ancient sediments and rocks record past changes in atmospheric composition due to chemical reactions with Earth's ...
- atmospheric brown cloud
- a layer of air pollution containing aerosols such as soot or dust that absorb as well as scatter incoming solar radiation, leading to regional and global climatic effects and posing risks to human health and food security. This layer extends from Earth's surface to an altitude of roughly 3 km ...
- atmospheric circulation
- any atmospheric flow used to refer to the general circulation of the Earth and regional movements of air around areas of high and low pressure. On average, this circulation corresponds to large-scale wind systems arranged in several east-west belts that encircle the Earth. In the subtropical high-pressure belts near latitudes ...
- atmospheric corona
- set of one or more coloured rings that sometimes appear close to the Sun or Moon when they are viewed through a thin cloud composed of water droplets. They are caused by the diffraction of light around the edges of the droplets, with each colour being deviated through a slightly ...
- atmospheric electricity
- electrical phenomena that occur in the lower atmosphere, usually the troposphere-e.g., the production, transport, and loss of free electrical charges; the change in electrical potential from point to point in the atmosphere; and the atmosphere's electrical conductivity. The term is not applied to phenomena in the ionosphere. Major fields of ...
- atmospheric optics
- study of optical characteristics and phenomena associated with the interaction of visible sunlight with atmospheric gases, particulates, and water vapour. Refraction, diffraction, Rayleigh scattering (qq.v.), and polarization of light are within the compass of atmospheric optics; the phenomena studied include rainbows, halos, atmospheric corona, mirages, and sundogs (see parhelion).
- atmospheric pressure
- force per unit area exerted by an atmospheric column (that is, the entire body of air above the specified area). Atmospheric pressure can be measured with a mercury barometer (hence the commonly used synonym barometric pressure), which indicates the height of a column of mercury that exactly balances the weight ...
- atmospheric refraction
- change in the direction of propagation of electromagnetic radiation or sound waves in traversing the atmosphere. Such changes are caused by gradients in the density of the air. See refraction.
- atmospheric science
- interdisciplinary field of study that combines the components of physics and chemistry that focus on the structure and dynamics of Earth's atmosphere. Mathematical tools, such as differential equations and vector analysis, and computer systems are used to evaluate the physical and chemical relations that describe the workings of the atmosphere.
- atmospheric turbulence
- small-scale, irregular air motions characterized by winds that vary in speed and direction. Turbulence is important because it mixes and churns the atmosphere and causes water vapour, smoke, and other substances, as well as energy, to become distributed both vertically and horizontally.
- atoll
- coral reef enclosing a lagoon. Atolls consist of ribbons of reef that may not always be circular but whose broad configuration is a closed shape up to dozens of kilometres across, enclosing a lagoon that may be approximately 50 m (160 feet) deep or more.
- atom
- smallest unit into which matter can be divided without the release of electrically charged particles. It also is the smallest unit of matter that has the characteristic properties of a chemical element. As such, the atom is the basic building block of chemistry.
- atomic bomb
- weapon with great explosive power that results from the sudden release of energy upon the splitting, or fission, of the nuclei of such heavy elements as plutonium or uranium.
- atomic clock
- type of clock that uses certain resonance frequencies of atoms (usually cesium or rubidium) to keep time with extreme accuracy. The electronic components of atomic clocks are regulated by the frequency of the microwave electromagnetic radiation. Only when this radiation is maintained at a highly specific frequency will it induce ...
- Atomic Energy Commission
- U.S. federal civilian agency established by the Atomic Energy Act, which was signed into law by President Harry S. Truman on Aug. 1, 1946, to control the development and production of nuclear weapons and to direct the research and development of peaceful uses of nuclear energy. On Dec. 31, 1946, ...
- atomic mass
- the quantity of matter contained in an atom of an element. It is expressed as a multiple of one-twelfth the mass of the carbon-12 atom, 1.992646481023gram, which is assigned an atomic mass of 12 units. In this scale 1 atomic mass unit (amu) corresponds to 1.660538781024gram.
- atomic number
- the number of a chemical element (q.v.) in the periodic system, whereby the elements are arranged in order of increasing number of protons in the nucleus. Accordingly, the number of protons, which is always equal to the number of electrons in the neutral atom, is also the atomic number. An ...
- atomic physics
- the scientific study of the structure of the atom, its energy states, and its interactions with other particles and with electric and magnetic fields. Atomic physics has proved to be a spectacularly successful application of quantum mechanics, which is one of the cornerstones of modern physics.
- atomic radius
- half the distance between the nuclei of identical neighbouring atoms in the solid form of an element. An atom has no rigid spherical boundary, but it may be thought of as a tiny, dense positive nucleus surrounded by a diffuse negative cloud of electrons. The value of atomic radii depends ...
- atomic theory
- ancient philosophical speculation that all things can be accounted for by innumerable combinations of hard, small, indivisible particles (called atoms) of various sizes but of the same basic material; or the modern scientific theory of matter according to which the chemical elements that combine to form the great variety of ...
- atomic time
- timescale generated by atomic clocks, which furnish time more accurately than was possible with previous astronomical means (measurements of the rotation of the Earth and its revolution about the Sun). International Atomic Time (TAI) is based on a system consisting of about 270 laboratory-constructed atomic clocks. Signals from these atomic ...
- atomic weight
- ratio of the average mass of a chemical element's atoms to some standard. Since 1961 the standard unit of atomic mass has been one-twelfth the mass of an atom of the isotope carbon-12. An isotope is one of two or more species of atoms of the same chemical element that ...
- atomism
- any doctrine that explains complex phenomena in terms of aggregates of fixed particles or units. This philosophy has found its most successful application in natural science: according to the atomistic view, the material universe is composed of minute particles, which are considered to be relatively simple and immutable and too ...
- Atoms for Peace speech
- speech delivered to the United Nations by U.S. Pres. Dwight D. Eisenhower on December 8, 1953 (see primary source document: Atoms for Peace). In this address, Eisenhower spelled out the necessity of repurposing existing nuclear weapons technology to peaceful ends, stating that it must be humanity's goal to discover "the ...
- Aton
- in ancient Egyptian religion, a sun god, depicted as the solar disk emitting rays terminating in human hands, whose worship briefly was the state religion. The pharaoh Akhenaton (reigned 1353-36 BCE) returned to supremacy of the sun god, with the startling innovation that the Aton was to be the only ...
- Aton Hymn
- the most important surviving text relating to the singular worship of the Aton, a new religious ideology espoused by the ancient Egyptian king Akhenaton of the 18th dynasty. During his reign Akhenaton returned to the supremacy of the sun god, with the startling innovation that the Aton was to be ...
- atonality
- in music, the absence of functional harmony as a primary structural element. The reemergence of purely melodic-rhythmic forces as major determinants of musical form in the Expressionist works of Arnold Schoenberg and his school prior to World War I was a logical, perhaps inevitable consequence of the weakening of tonal ...
- atonement
- the process by which a person removes obstacles to his reconciliation with God. It is a recurring theme in the history of religion and theology. Rituals of expiation and satisfaction appear in most religions, whether primitive or developed, as the means by which the religious person reestablishes or strengthens his ...
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