Gentileschi \Jan-te-'les-ke\, Artemisia (b. 1593, Rome, Papal States—d. 1652/53, Naples, Kingdom of Naples) Italian painter. The daughter of Orazio Gentileschi, she studied with him and with the land¬ scape painter Agostino Tassi. Her earliest known work is Susanna and the Elders (1610), formerly attributed to Orazio. She was raped by Tassi, and, when he did not fulfill his promise to marry her, Orazio Gentileschi brought him to trial in 1612. During that event she herself was forced to give evidence under torture. In 1616 she joined the Academy of Design in Florence and began to develop a powerful style of her own. She was one of the greatest of Caravaggio’s followers in the Baroque style. Although her compositions were graceful, her subject matter was often violent; she illustrated such subjects as the story from the Apocrypha of Judith, the Jewish heroine, beheading Holofemes, an invading general. She worked in Rome and Naples and spent three years with her father in London (1638—41). The first woman artist to attain an international repu¬ tation, she is admired today as the earliest to show a feminist conscious¬ ness in her work.
Gentileschi, Orazio orig. Orazio Lomi (b. 1562, Pisa—d. c. 1639, London, Eng.) Italian painter. He went to Rome c. 1576-78 and painted frescoes in various churches (c. 1590-1600). His paintings of the early 17th century reveal the influence of Caravaggio’s strong chiaroscuro and contemporary figure types; though more refined than Caravaggio’s works, they lack the master’s power and uncompromising realism. Invited to England by Charles I in 1626, he remained there as court painter the rest of his life. Artemisia Gentileschi was his daughter. See photograph on oppo¬ site page.
Gentz Vgents\, Friedrich (b. May 2, 1764, Breslau, Silesia, Prussia—d. June 9, 1832, Vienna, Austria) German political journalist. Strongly influ-
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genus ► Geometric style I 749
enced by Edmund Burke, he published journals and pamphlets analyzing events from the viewpoint of a conservative liberal and compared the French Revolution unfavorably to the American Revolution. After serving in the Prussian civil service (1785-1803), he moved to Vienna, where he became from 1812 the propagandist and confidential adviser for Klemens, prince von Metternich. He served as secretary-general to the various con¬ gresses that convened after Napoleon’s defeat.
genus Biological classification. It ranks below family and above spe¬ cies, consisting of structurally or phylogenetically (see phylogenetic tree) related species or a single species exhibiting unusual differences. For example, the species of roses collectively form the genus Rosa and those of horses, donkeys, and zebras form the genus Equus. The genus name, capitalized and usually italicized, is the first word of a scientific name in the system of binomial nomenclature.
geochemical cycle Developmental path followed by individual ele¬ ments or groups of elements in the crustal and subcrustal zones of the Earth and on its surface. The concept encompasses geochemical differ¬ entiation (natural separation and concentration of elements) and heat- assisted recombination processes. Changes may not be apparent over a short term, but over a long term changes of great magnitude occur, includ¬ ing the evolution of continents and oceans.
geochemistry Scientific discipline dealing with the relative abun¬ dance, distribution, and migration of the Earth’s chemical elements and their isotopes. Historically, geochemistry was concerned primarily with defining elemental abundances in minerals and rocks. Modem geochem¬ ical research also includes study of the continual recycling of the Earth’s constituent materials through geologic processes, the cyclic flow of indi¬ vidual elements (and their compounds) between living and nonliving sys¬ tems, and certain areas of cosmology.
geochronology Dating and interpretation of geologic events in the history of the Earth. The classical technique of geochronology was stratig¬ raphy, including faunal succession. Since the mid 20th century, radiomet¬ ric dating has provided absolute age data to supplement the relative dates obtained from the fossil record. Radiometric dating is based on the prin¬ ciple that radioactive isotopes in geologic material decay at constant, known rates to daughter isotopes. See also carbon- 14 dating.
geode Hollow mineral body found in limestones and some shales, com¬ monly a slightly flattened globe 1-12 in. (2.5-30 cm) in diameter and containing a chalcedony layer surrounding an inner lining of crystals. The hollow interior often is nearly filled with inward-projecting crystals, new layers growing on top of old. The crystals are often of quartz but some¬ times of other minerals.
geodesy \je-'a-do-se\ Scientific discipline concerned with the size and shape of the Earth, its gravitational field, and the location of fixed points. Originally, all geodesic work was based on land surveys. Now satellites are used in conjunction with the land-based system.
geoduck Vgu-e-,dak\ Marine bivalve ( Panopea generosa ) that inhabits the intertidal zone of the Pacific coast from southern Alaska to Baja California. It is the largest known burrowing bivalve, with a shell about 7-9 in. (18-23 cm) long and siphons that extend up to about 4 ft (1.3 m). It may weigh as much as 8 lbs (3.6 kg). Though highly prized for food, it lives in deep bur¬ rows and is difficult to dig out (the name probably derives from an Indian phrase meaning “dig deep”). Similar species are found in other parts of the world.
Geoffrey of Monmouth Vjef- re...'man-moth \ (d. 1155) Medieval British chronicler. He was probably an Oxford cleric for most of his life. His mostly fictional History of the Kings of Britain (c. 1135-39) traced the descent of British princes from the Trojans; it brought the figure of
Arthur (see Arthurian legend) into European literature and introduced the enchanter Merlin, whose story Geoffrey related in the Vita Merlini (c. 1148-51?). Though denounced from the first by other historians, the His¬ tory was one of the most popular books of the Middle Ages and had an enormous influence on later chroniclers.
geographic information system (GIS) Computerized system that relates and displays data collected from a geographic entity in the form of a map. The ability of GIS to overlay existing data with new informa¬ tion and display it in colour on a computer screen is used primarily to conduct analyses and make decisions related to geology, ecology, land use, demographics, transportation, and other domains, most of which relate to the human use of the physical environment. Through the process of geocoding, geographic data from a database is converted into images in the form of maps.
geography Science of the Earth’s surface, which describes and ana¬ lyzes the spatial variations in physical, biological, and human phenom¬ ena that occur on the surface of the globe and treats their interrelationships and their significant regional patterns. Once associated entirely with map¬ ping and the exploration of the Earth, the field today is wide-ranging, and geographers use a variety of methods and techniques drawn from numer¬ ous disciplines. Subfields of geography include physical, human, and regional geography, which may range in scale from worldwide to a con¬ tinent, a country, or a city.
geologic oceanography See marine geology
geologic time Interval of time occupied by the Earth’s geologic his¬ tory, extending from c. 3.9 billion years ago (corresponding to the age of the oldest known rocks) to the present day. It is, in effect, the part of the Earth’s history that is recorded in rock strata. The geologic time scale is classified in nested intervals distinguished by characteristic geologic and biologic features. From longest to shortest duration, the intervals are eon, era, period, and epoch See table on following page.