Hyksos \'hik-,s6s\ Group of mixed Semitic-Asiatics who settled in northern Egypt in the 18th century bc. They seized power c. 1630 bc and ruled Egypt for 108 years thereafter. They were superficially Egyptian- ized and did not interfere with Egyptian culture. Their chief deity was Seth, whom they identified with an Asiatic storm god. The Hyksos intro¬ duced the horse and chariot, the compound bow, improved battle-axes, and advanced fortification techniques. Hyksos pharaohs tried to halt the spread of a Theban revolt, but their dynasty fell to Ahmose in 1521 bc.
hylomorphism \ l hl-b- , m6r- l fiz-9m\ Metaphysical view according to which every natural body consists of two intrinsic principles, one poten¬ tial (namely, primary matter) and one actual (namely, substantial form). It was the central doctrine of Aristotle’s philosophy of nature. He based his argument for hylomorphism chiefly on the analysis of change. If a being changes (e.g., from being cold to being hot), something permanent must exist that remains throughout the change; in addition, there must be an actual principle that differentiates the earlier from the later state. The permanent principle is matter, the actual principle form.
hylozoism \ l hI-b- , zo- l iz-3m\ View that all matter is alive, either in itself or by participation in the operation of a world soul or some similar prin¬ ciple. Hylozoism is logically distinct both from early forms of animism, which personify nature, and from panpsychism, which attributes some form of consciousness or sensation to all matter. The word was coined in the 17th century by Ralph Cudworth, who with Henry More (1614-1687) spoke of “plastic nature,” an unconscious, incorporeal substance that con¬ trols and organizes matter and thus produces natural events as a divine instrument of change.
Hymen Greek god of marriage. He was usually thought to be a son of Apollo by one of the Muses, perhaps Calliope. Other accounts called him the son of Dionysus and Aphrodite. In Attic legend he was a beautiful youth who rescued a group of young women, including his beloved, from a gang of pirates. He obtained the girl in marriage, and their happy life was invoked in many wedding songs.
hymn Song used in Christian worship, usually sung by the congrega¬ tion and written in stanzas with rhyme and metre. The term comes from the Greek hymnos (“song of praise”), but songs in honour of God or the gods exist in all civilizations. Christian hymnody grew out of the singing of psalms in the Temple of Jerusalem. The earliest known Christian hymn dates from c. ad 200. Hymns were prominent in the Byzantine liturgy from early times, and in the Western church they were sung by congre¬ gations until the Middle Ages, when choirs took over hymn singing. Con¬ gregational singing was reestablished during the Reformation. Martin Luther and his followers were great hymn writers, while the Calvinists preferred setting psalms to music. The compositions of Isaac Watts and John Wesley were notable in English hymnody. The Counter-Reformation led to the composition of many Roman Catholic hymns, and the Roman Catholic church restored congregational singing of hymns after the Sec¬ ond Vatican Council in the 1960s.
Hyndman Vhlnd-msnV Henry M(ayers) (b. March 7, 1842, Lon¬ don, Eng.—d. Nov. 22, 1921, London) British Marxist political leader. Educated at the University of Cambridge, he worked as a journalist before founding the socialist Democratic Federation, and in England for All (1881), the first English socialist book in almost 50 years, he expounded the ideas of Karl Marx. He steered many British socialists toward Marx¬ ism, but Friedrich Engels, who disliked Hyndman, encouraged many to break away and form the Socialist League. During World War I Hyndman took a patriotic and pro-French line, causing his ouster from the Socialist Party, whereupon he formed the National Socialist Party (1916), later renamed the Social Democratic Federation.
hyperactivity See attention deficit disorder
hyperbaric chamber \,hl-p9r-'bar-ik\ 0 / decompression cham¬ ber or recompression chamber Sealed chamber supplying a high- pressure atmosphere. Breathing air at high pressure increases the oxygen level in tissues. This is used to inhibit growth of anaerobic bacteria (as in tetanus or gas gangrene); to increase the chance that babies with certain heart malformations will survive heart surgery; or to cause air bubbles (as in air embolism or decompression sickness) to be redissolved, carried to the lungs, and exhaled as pressure is gradually returned to normal.
hyperbola \hl-'p9r-b3-la\ Curve with two separate branches, one of the conic sections. In Euclidean geometry, the intersection of a double right cir¬ cular cone and a plane at an angle that is less than the cone’s generating angle (the angle its sides make with its central axis) forms the hyperbo¬ la’s two branches (one on each nappe, or single cone). In analytic geom¬ etry, the standard equation of a hyperbola is x 2 /^ 2 - y 2 / b 2 = 1. Hyperbolas have many important physical attributes that make them useful in the design of LENSes and antennas.
hyperbolic \,hl-p3r-'ba-lik\ function In mathematics, one of a set of functions related to the hyperbola in the same way the trigonometric func¬ tions relate to the circle. They are the hyperbolic sine, cosine, tangent, secant, cotangent, and cosecant (written “sinh,” “cosh,” etc.). The hyper¬ bolic equivalent of the fundamental trigonometric identity is cosh 2 z - sinh 2 z = 1. The hyperbolic sine and cosine, particularly useful for finding special types of integrals, can be defined in terms of exponential functions: sinhx = (e — e ~ x ) 4- 2 and coshx = (e + e ~ x ) -4 2
hyperbolic geometry Non-Euclidean geometry, useful in modeling interstellar space, that rejects the parallel postulate, proposing instead that at least two lines through any point not on a given line are parallel to that line. Though many of its theorems are identical to those of Euclidean geometry, others differ. For example, two parallel lines converge in one direction and diverge in the other, and the angles of a triangle add up to less than 180°.
hypernephroma See renal carcinoma
hypertension or high blood pressure Condition in which blood pressure is abnormally high. Over time, it damages the kidneys, brain, eyes, and heart. Hypertension accelerates atherosclerosis, increasing the risk of heart attack, stroke, and kidney failure. More common in the elderly and blacks, it usually has no symptoms but can be detected by a routine blood- pressure test. Secondary hypertension, caused by another disorder (most often kidney disease or hormone imbalance), accounts for 10% of cases. The other 90% have no specific cause (essential hypertension). A low-salt diet, weight loss, smoking cessation, limited alcohol intake, and exercise can prevent or treat hypertension or reduce medication if drug therapy proves necessary. Malignant hypertension, a severe, rapidly progressing form, requires emergency treatment with drugs to dilate the blood vessels.
hypertext or hyperlink Linking of related information by electronic connections in order to allow a user easy access between them. Concep¬ tualized by Vannevar Bush (1945) and invented by Douglas Engelbart in the 1960s, hypertext is a feature of some computer programs that allows the user to select a word and receive additional information, such as a definition or related material. In Internet browsers, hypertext links (hot- links) are usually denoted by highlighting a word or phrase with a dif¬ ferent font or colour. Hypertext links create a branching or network structure that permits direct, unmediated jumps to related information. Hypertext has been used most successfully as an essential feature of the World Wide Web (see HTML; HTTP). Hyperlinks may also involve objects other than text (e.g., selecting a small picture may provide a link to a larger version of the same picture).