Ionian revolt Uprising (499-494 bc) of some of the Ionian cities of Asia Minor against their Persian overlords. The cities deposed their own tyrants and, with help from Athens, tried unsuccessfully to throw off Per¬ sian domination. Darius I of Persia used Athens’s involvement as a pre¬ text for his invasion of Greece in 490, initiating the Persian Wars, which resulted in a stronger Athenian influence in western Anatolia.
Ionian school School of Greek philosophers of the 6th-5th century bc, including Thales, Anaximander, Anaximenes, Heracleitus, Anaxagoras, Dio¬ genes of Apollonia, Archelaus, and Hippon. Though Ionia was the origi¬ nal center of their activity, they differed so greatly from one another in their conclusions that they cannot truly be said to represent a specific school of philosophy, but their common concern to explain phenomena in terms of matter or physical forces distinguished them from later think¬ ers.
Ionian Sea Part of the Mediterranean Sea lying between Greece, Sic¬ ily, and Italy. Though once considered part of the Adriatic Sea, to which it connects by the Strait of Otranto, it is now considered a separate body. The Mediterranean reaches its greatest depth (16,000 ft or 4,900 m) in the Ionian south of Greece. Along its eastern shore are the Ionian Islands.
ionic bond Electrostatic attraction between oppositely charged ions in a chemical compound. Such a bond forms when one or more electrons are transferred from one neutral atom (typically a metal, which becomes a cation) to another (typically a nonmetallic element or group, which becomes an anion). The two types of ion are held together by electrostatic forces in a solid that does not comprise neutral molecules as such; rather, each ion has neighbours of the opposite charge in an ordered overall crys¬ talline structure. When, for example, crystals of common salt (sodium chloride, NaCl) are dissolved in water, they dissociate (see dissociation) into two kinds of ions in equal numbers, sodium cations (Na + ) and chlo¬ ride anions (Cl - ). See also bonding; covalent bond.
ionization Process by which electrically neutral atoms or molecules are converted to electrically charged atoms or molecules (ions) by the removal or addition of negatively charged electrons. It is one of the principal ways in which radiation transfers energy to matter, and hence of detecting radia¬ tion. In general, ionization occurs whenever sufficiently energetic charged particles or radiant energy travels through gases, liquids, or solids. A cer¬ tain minimal level of ionization is present in the earth’s atmosphere because of continuous absorption of cosmic rays from space and ultravio¬ let radiation from the sun.
ionization potential or ionization energy Amount of energy required to remove an electron from an isolated atom or molecule. There is an ionization potential for each successive electron removed, though that associated with removing the first (most loosely held) electron is most commonly used. The ionization potential of an element is a measure of its ability to enter into chemical reactions requiring ion formation or dona¬ tion of electrons and is related to the nature of the chemical bonding in the compounds formed by elements. See also binding energy, ionization.
ionosphere M-'an-a-.sfirX Region of the Earth’s atmosphere in which the number of ions, or electrically charged particles, is large enough to affect the propagation of radio waves. The ionosphere begins at an alti¬ tude of about 30 mi (50 km) but is most distinct above about 50 mi (80 km). The ionization is caused mainly by solar radiation at X-ray and ultra¬ violet wavelengths. The ionosphere is responsible for the long-distance propagation, by reflection, of radio signals in the shortwave and broad¬ cast bands.
Iowa State (pop., 2000: 2,926,324), midwestem U.S. Bordered by Min¬ nesota, Wisconsin, Illinois, Missouri, Nebraska, and South Dakota, it cov¬
ers 56,276 sq mi (145,755 sq km). Its capital is Des Moines. The Des Moines River flows across the state from northwest to southeast. The Mis¬ sissippi River forms its eastern boundary, while the Missouri River and the Big Sioux River define portions of its western boundary. The Sauk, Fox, Iowa, and Sioux Indians lived in the region when French explorers Louis Jolliet and Jacques Marquette arrived in 1673. The U.S. acquired Iowa as part of the Louisiana Purchase in 1803. Following the Black Hawk War and purchase of eastern Iowa from the Sauk and Fox Indians in the 1830s, white settlement advanced rapidly. Iowa became a territory in 1838 and was made the 29th state in 1846. After the Civil War, railroad expansion drew large waves of immigrants from the east and from Europe. After World War I population growth slowed. Its economy is based on agricul¬ ture, and Iowa is a leader in the U.S. production of livestock.
IP address in full Internet Protocol address Number that uniquely identifies each computer on the Internet. A computer’s IP address may be permanently assigned or supplied each time that it connects to the Internet by an Internet service provider. In order to accommodate the extraordinary growth in the number of devices connected to the Internet, a 32-bit protocol standard, known as IPv4, began to be replaced by a 128- bit protocol, IPv6, in 2000. See also TCP/IP; domain name; URL.
ipecac \'i-pi-,kak\ or ipecacuanha \,i-pi- I ka-kyo- , wa-n3\ Dried rhi¬ zome and roots of either of two tropical New World plants ( Cephaelis acuminata and C. ipecacuanha ) of the madder family. It has been used since ancient times especially as a source of a drug to treat poisoning by induc¬ ing nausea and vomiting. The name also refers to the drug itself.
Iphigeneia U-fo-jo-'nI-oX In Greek mythology, the eldest daughter of Agamemnon and Clytemnestra and sister of Electra and Orestes. When the Achaean fleet was becalmed at Aulis, Iphigeneia’s father sacrificed her to Artemis in order to secure favourable winds to carry the ships to Troy. Her mother later avenged her death by murdering Agamemnon. Iphigeneia’s story is treated in plays by Aeschylus, Sophocles, and Euripides. According to Euripides, she did not die but was saved by Artemis; she went to the land of Tauris, where she became a priestess, and she saved Orestes from madness and death when he fled there after killing their mother.
Ipoh \'e-po\ City (pop., 2000 prelim.: 566,211), western Malaysia. Its name comes from a local tree, whose poisonous resin was once used by indigenous people for hunting. The modern city dates from the 1890s, when British tin-mining companies were set up. Immigrant Chinese were brought in to work the tin deposits, and their descendants now dominate the city. It is the country’s mining capital.
Ipsus, Battle of (301 bc) Battle marking the defeat at Ipsus, Phrygia, of Antigonus I Monophthalmus and his son Demetrius I Poliorcetes at the hands of Lysimachus of Thrace, Seleucus I Nicator of Babylon, Ptolemy I Soter of Egypt, and Cassander of Macedonia. Antigonus was killed and his Asian territory lost, but Demetrius kept territory in Greece and Mace¬ donia. The battle was part of the struggle for control of territories that made up Alexander the Great’s empire.
Ipswich Town and borough (pop., 2001: 117,074), administrative and historic county seat of Suffolk, England. Located northeast of London, it was chartered in 1200. It prospered as a port for the export of East Anglian textiles from medieval times to the 17th century. It is now an agricultural market and service centre. Its landmarks include the 16th-century Christchurch mansion and the Great White Horse coaching inn mentioned in Charles Dickens’s The Pickwick Papers. It was the birthplace of Tho¬ mas Cardinal Wolsey.
IQ in full intelligence quotient Number intended to represent a mea¬ sure of relative intelligence as determined by the subject’s responses to a series of test problems. The IQ was originally computed as the ratio of a person’s mental age to his or her chronological (physical) age, multiplied by 100, but use of the concept of mental age has been largely discontin¬ ued, and IQ is now generally assessed on the basis of the statistical dis¬ tribution of scores. The most widely used intelligence tests are the Stanford-Binet test (1916), for children, and the Wechsler test (1939), originally for adults but now also for children. A score above 130 is con¬ sidered to reflect “giftedness,” while a score below 70 is considered to reflect mental impairment or mental retardation. Intelligence tests have provoked great controversy, particularly about what kinds of mental abil¬ ity constitute intelligence and whether IQ adequately represents these abilities, and about cultural and class bias in test construction and stan¬ dardization procedures.