microsurgery or micromanipulation Surgical technique for oper¬ ating on minute structures, with specialized, tiny precision instruments under observation through a microscope, sometimes equipped with cam¬ eras to show the operation on a monitor. Microsurgery permits operations that were once impossible—surgery on the delicate bones of the inner and middle ear, reattachment of severed limbs or digits, repair of the retina, and removal of tumours intricately embedded in vital structures.
microtubule \ l mI-kro- , tii-byiil\ Tubular structure enclosed by a mem¬ brane found within animal and plant cells. Of varying length, they have several functions. They help give shape to many cells and are major com¬ ponents of cilia and flagella, participate in the formation of the spindle during cell division (mitosis), and assist the movement of vesicles from the cell bodies of nerve cells toward the ends of those cells’ long exten¬ sions (axons) and back to the cell bodies.
microwave Portion of the electromagnetic spectrum that is situated between radio waves and infrared radiation. Microwaves have wavelengths ranging from 30 cm to 1 mm, corresponding to frequencies from about 1 gigahertz (10 9 Hz) to 1 terahertz (10 12 Hz). They are the principal car¬ riers of television, telephone, and data transmissions between stations on Earth and between the Earth and satellites. Radar beams are short pulses of microwaves used to locate ships and planes, track weather systems, and determine the speeds of moving objects. Microwaves are absorbed by water and fat in foodstuffs and produce heat from the inside (see micro- wave oven). Materials such as glass and ceramics do not absorb micro- waves, and metals reflect them. See also maser.
microwave oven Appliance that cooks food by means of high- frequency electromagnetic radiation. A microwave oven is a relatively small, boxlike oven that raises the temperature of food by subjecting it to a high-frequency electromagnetic field. The microwaves are absorbed by water, fats, sugars, and certain other molecules, whose resulting vibra¬ tions produce heat. The heating thus occurs inside the food, without warm¬ ing the surrounding air. This process greatly reduces cooking time; baking
and other tasks that may require an hour or more in a conventional oven can be completed in minutes in a microwave oven.
Mid-Atlantic Ridge Submarine ridge lying along the floor of the cen¬ tral Atlantic Ocean. It is a long mountain chain running about 10,000 mi (16,000 km) in a north-south direction, curving from the Arctic Ocean to the southern tip of Africa. The mountains sometimes reach above sea level, forming such islands or island groups as Ascension, Saint Helena, and Tristan da Cunha.
mid-ocean ridge See oceanic ridge
Midas Vml-d9s\ In Greek and Roman legend, a king of Phrygia. Midas captured the satyr Silenus but treated him kindly, and as a reward was granted a wish by Dionysus. He asked that everything he touched turn to gold; but after turning his daughter to gold when she embraced him, he asked to be released from his wish. In another legend Midas was invited to judge a music contest between Apollo and the satyr Marsyas. When Midas decided against Apollo, Apollo punished him by giving him don¬ key’s ears. See also satyr and silenus.
Midas See Missile Defense Alarm System
Middle Ages Period in European history traditionally dated from the fall of the Roman Empire to the dawn of the Renaissance. In the 5th cen¬ tury the Western Roman Empire endured declines in population, economic vitality, and the size and prominence of cities. It also was greatly affected by a dramatic migration of peoples that began in the 3rd century. In the 5th century these peoples, often called barbarians, carved new kingdoms out of the decrepit Western Empire. Over the next several centuries these kingdoms oversaw the gradual amalgamation of barbarian, Christian, and Roman cultural and political traditions. The longest-lasting of these king¬ doms, that of the Franks, laid the foundation for later European states. It also produced Charlemagne, the greatest ruler of the Middle Ages, whose reign was a model for centuries to come. The collapse of Charlemagne’s empire and a fresh wave of invasions led to a restructuring of medieval society. The 11th—13th centuries mark the high point of medieval civili¬ zation. The church underwent reform that strengthened the place of the pope in church and society but led to clashes between the pope and emperor. Population growth, the flourishing of towns and farms, the emer¬ gence of merchant classes, and the development of governmental bureau¬ cracies were part of cultural and economic revival during this period. Meanwhile, thousands of knights followed the call of the church to join the Crusades. Medieval civilization reached its apex in the 13th century with the emergence of Gothic architecture, the appearance of new reli¬ gious orders, and the expansion of learning and the university. The church dominated intellectual life, producing the Scholasticism of St. Thomas Aquinas. The decline of the Middle Ages resulted from the breakdown of medieval national governments, the great papal schism, the critique of medieval theology and philosophy, and economic and population collapse brought on by famine and disease.
Middle Congo See Republic of the Congo
Middle East or Mideast or Near East Geographic region where Europe, Africa, and Asia meet. It is an unofficial and imprecise term that now generally encompasses the lands around the southern and eastern shores of the Mediterranean Sea—notably Egypt, Jordan, Israel, Leba¬ non, and Syria—as well as Iran, Iraq, and the countries of the Arabian Peninsula. Afghanistan, Libya, Turkey, and The Sudan are sometimes also included. The term was formerly used by Western geographers and his¬ torians to describe the region from the Persian Gulf to Southeast Asia; Near East is sometimes used to describe the same area.
Middle English Vernacular spoken and written in England c. 1100— 1500, the descendant of Old English and the ancestor of Modern English. It can be divided into three periods: Early, Central, and Late. The Central period was marked by the borrowing of many Anglo-Norman words and the rise of the London dialect, used by such poets as John Gower and Geoffrey Chaucer in a 14th-century flowering of English literature. The dialects of Middle English are usually divided into four groups: South¬ ern, East Midland, West Midland, and Northern.
Middle West See Midwest
Middlebury College Private liberal arts college in Middlebury, Vt., founded in 1800. It is known for its curriculum emphasizing writing, lit¬ erature, and modern languages. Middlebury sponsors the Bread Loaf Writ¬ ers’ Conference, an annual gathering for established and aspiring authors.
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Middlesbrough Vmi-d^z-broX Town and unitary authority (pop., 2001: 134,487), geographic county of North Yorkshire, historic county of Yorkshire, England. Situated on the southern bank of the River Tees, it was formed in 1830 with the arrival of the railway to the site of a new coal-exporting port. Its development was later fostered by the discovery of ironstone nearby.