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thermal fusion: change of a solid into a liquid when heat is applied. In a pure crystalline solid, this process occurs at a fixed temperature called the melting point (q.v.); an impure ...
thermal neutron: any free neutron (one that is not bound within an atomic nucleus) that has an average energy of motion (kinetic energy) corresponding to the average energy of the particles of ...
thermal radiation: process by which energy, in the form of electromagnetic radiation, is emitted by a heated surface in all directions and travels directly to its point of absorption at the speed ...
thermal window: in Classical architecture, semicircular window divided into three sections by two mullions, or vertical strips. The base of the central section of a thermal window is wider than that of ...
Thermidorian Reaction: in the French Revolution, the revolt initiated on 9 Thermidor, year II (July 27, 1794), which resulted in the fall of Maximilien Robespierre and the collapse of revolutionary fervour and ...
thermionic emission: discharge of electrons from heated materials, widely used as a source of electrons in conventional electron tubes (e.g., television picture tubes) in the fields of electronics and communications. The phenomenon ...
thermionic power converter: any of a class of devices that convert heat directly into electricity rather than first changing it to some other form of energy.
thermistor: electrical-resistance element made of a semiconducting material consisting of a mixture of oxides of manganese and nickel; its resistance varies with temperature. Thermistors (temperature-sensitive, or thermal, resistors) are used as ...
Thermit: powdered mixture used in incendiary bombs, in the reduction of metals from their oxides, and as a source of heat in welding iron and steel and in foundry work.
thermocline: oceanic water layer in which water temperature decreases rapidly with increasing depth. A widespread permanent thermocline exists beneath the relatively warm, well-mixed surface layer, from depths of about 200 m ...
thermocouple: a temperature-measuring device consisting of two wires of different metals joined at each end. One junction is placed where the temperature is to be measured, and the other is kept ...
thermodynamic equilibrium: condition or state of a thermodynamic system, the properties of which do not change with time and that can be changed to another condition only at the expense of effects ...
thermodynamics: systematic study of the relationship between heat, work, temperature, and energy, now encompassing the general behaviour of physical systems in a condition of equilibrium or close to it. It is ...
thermoelectric power generator: any of a class of devices that either convert heat directly into electricity or transform electrical energy into pumped thermal power for heating or cooling. Such devices are based on ...
thermokarst: land-surface configuration that results from the melting of ground ice in a region underlain by permafrost. In areas that have appreciable amounts of ice, small pits, valleys, and hummocks are ...
thermoluminescence: emission of light from some minerals and certain other crystalline materials. The light energy released is derived from electron displacements within the crystal lattice of such a substance caused by ...
thermometry: the science of measuring the temperature of a system or the ability of a system to transfer heat to another system. Temperature measurement is important to a wide range of ...
thermonatrite: a carbonate mineral, hydrated sodium carbonate (Na₂CO₃·H₂O), found near saline lakes as an evaporation product or on arid soil as an efflorescence. It is usually associated with natron (Na₂CO₃·10H₂O) and ...
thermonuclear bomb: weapon whose enormous explosive power results from an uncontrolled, self-sustaining chain reaction in which isotopes of hydrogen combine under extremely high temperatures to form helium in a process known as ...
thermonuclear reaction: fusion of two light atomic nuclei into a single heavier nucleus by a collision of the two interacting particles at extremely high temperatures, with the consequent release of a relatively ...
thermoperiodicity: the growth or flowering responses of plants to alternation of warm and cool periods. Daily temperature fluctuations produce dramatic effects on the growth or flowering of most plants. The lack ...
Thermopolis: resort town, seat (1913) of Hot Springs county, north-central Wyoming, U.S., on the Bighorn River, opposite East Thermopolis. The site was originally within the Wind River Indian Reservation (Shoshone and ...
Thermopylae: narrow pass on the east coast of central Greece between the Kallidhromon massif and the Maliakos Gulf, about 85 miles (136 km) northwest of Athens. In antiquity its cliffs were ...
thermoreception: process in which different levels of heat energy (temperatures) are detected by living things.
thermoregulation: the maintenance of an optimum temperature range by an organism. Cold-blooded animals (poikilotherms) pick up or lose heat by way of the environment, moving from one place to another as ...
thermosphere: region of increasing temperature above the mesosphere. The base of the thermosphere (the mesopause) is at an altitude of about 80 km (50 miles), whereas its top (the thermopause) is ...
thermostat: device to detect temperature changes for the purpose of maintaining the temperature of an enclosed area essentially constant. In a system including relays, valves, switches, etc., the thermostat generates signals, ...
theropod: any member of the dinosaur subgroup, Theropoda, that includes all the flesh-eating dinosaurs. Theropods were the most diverse group of saurischian ("lizard-hipped") dinosaurs, ranging from the crow-sized
Theroux, Paul: American novelist and travel writer known for his highly personal observations on many locales.
Thesaurus Linguae Latinae: dictionary of the Latin language, published at Leipzig, the most important and definitive such undertaking of modern times. It is being prepared by the Universities of Berlin, Gottingen, Leipzig, and ...
Thesavalamai: traditional law of the Tamil country of northern Sri Lanka, codified under Dutch colonial rule in 1707. The Dutch, to facilitate the administration of their colonial territories in Ceylon, established ...
Theseum: temple in Athens dedicated to Hephaestus and Athena as patrons of the arts and crafts. Its style indicates that this, the best-preserved ancient Greek temple in the world, is slightly ...
Theseus: great hero of Attic legend, son of Aegeus, king of Athens, and Aethra, daughter of Pittheus, king of Troezen (in Argolis), or of the sea god, Poseidon, and Aethra. Legend ...
Thesmophoria: in Greek religion, ancient festival held in honour of Demeter Thesmophoros and celebrated by women in many parts of the Greek world. The meaning of the name Demeter Thesmophoros still ...
Thespiae: ancient Greek city of Boeotia by the Thespius (modern Kanavari) River and at the eastern foot of Mt. Helicon; site of the "Eros" of Praxiteles, one of the most famous ...
Thespis: Attic Greek poet from the deme (district) of Icaria who reputedly originated the actor's role in drama. He was often considered the "inventor of tragedy," and his name is recorded ...
Thessalonians, letters of Paul to the: two New Testament letters written by Paul from Corinth, Greece, about AD 50 and addressed to the Christian community he had founded in Macedonia.
Thessaloniki: city, capital and residence of the minister for northern Greece and administrative centre of the nomos (department) of Thessaloniki, on the west side of the Chalcidice (Khalkidhiki) peninsula at the ...
Thessaly: region of northern Greece south of Macedonia, lying between upland Epirus and the Aegean Sea and comprising chiefly the fertile Trikala and Larissa lowlands. It is well delineated by topographical ...
Thetford: town ("parish"), Breckland district, administrative and historic county of Norfolk, England. The town lies on the edge of Thetford Chase Forest. It possesses the remains of a Cluniac priory, a ...
Thetford-Mines: city, Chaudiere-Appalaches region, southern Quebec province, Canada. Originating after the discovery of asbestos deposits there in 1876, it was called Kingsville and later renamed after Thetford, Norfolk, Eng. Situated 60 ...
Thetis: in Greek mythology, a Nereid loved by Zeus and Poseidon. When Themis (goddess of Justice), however, revealed that Thetis was destined to bear a son who would be mightier than ...
Theudis: the first Visigothic king of Spain (531-548), in the sense that he was the first to reside there permanently. An Ostrogoth, he had acquired great possessions in the valley of ...
thiamin: water-soluble organic compound that is necessary for carbohydrate metabolism in both plants and animals. It carries out these functions in its active form, as a component of the coenzyme thiamin ...
thiazine: any of three organic compounds of the heterocyclic series, having molecular structures that include a ring of four atoms of carbon and one each of nitrogen and sulfur.
thiazole: any of a class of organic compounds of the heterocyclic series characterized by a ring structure composed of three carbon atoms, one nitrogen atom, and one sulfur atom. This ring ...
Thibaud, Jacques: French violinist known for his performances of Mozart, Beethoven, and 19th-century French works.
Thibaut, Anton Friedrich Justus: German jurist and leader of the philosophical school that maintained the tradition of natural law in a spirit of moderate rationalism. He is remembered chiefly because his call for the ...
Thibaw: last king of Burma, whose short reign (1878-85) ended with the occupation of Upper Burma by the British.
Thibodaux: city, seat (1808) of Lafourche parish, southeastern Louisiana, U.S., on Bayou Lafourche, 49 miles (79 km) southwest of New Orleans. The area was occupied by the Colapissa Indians in the ...
thick-headed fly: an elongated, wasplike insect of the family Conopidae (order Diptera). It is brownish in colour, often with yellow markings, and between about 6 and 25 millimetres (0.2 and 1 inch) ...
thickhead: any of about 35 species constituting the songbird family Pachycephalidae (order Passeriformes), considered by some authors to be a subfamily of Muscicapidae. Thickheads have heavy-looking, seemingly neckless foreparts and are ...
thickknee: any of numerous shorebirds that constitute the family Burhinidae (order Charadriiformes). The bird is named for the thickened intertarsal joint of its long, yellowish or greenish legs; or, alternatively, for ...
Thierry: count of Flanders (1128-68), son of Thierry II, duke of Upper Lorraine, and Gertrude, daughter of Robert I the Frisian, count of Flanders. He contested the county of Flanders with ...
Thierry De Chartres: French theologian, teacher, encyclopaedist, one of the foremost thinkers of the 12th century.
Thierry, Augustin: French historian whose discursive method of presenting history in picturesque and dramatic terms makes him one of the outstanding Romantic historians.
Thiers, Adolphe: French statesman, journalist, and historian, a founder and the first president (1871-73) of the Third Republic. His historical works include a 10-volume Histoire de la revolution francaise and a 20-volume ...
Thies: city, west-central Senegal. Situated 35 miles (56 km) east of Dakar, it is an important transportation centre, serving as the junction of the eastern Dakar-Niger River railway and the northern ...
Thietmar: also spelled Dietmar, or Dithmar bishop of Merseburg and chronicler whose history of the three Ottos and Henry II, Saxon kings of Germany and Holy Roman emperors, is an important ...
thigmotrich: any protozoan of the ciliate order Thigmotrichida, found living parasitically in and about the gills or in the mantle cavity of bivalve mollusks. On the anterior part of the cell ...
Thika: town, south-central Kenya. It lies in the highland region just northeast of the capital city of Nairobi, at an elevation of 4,943 feet (1,507 m) above sea level. Situated in ...
Thimann, Kenneth V.: English-born American plant physiologist who isolated auxin, an important plant growth hormone.
thimble: small, bell-shaped implement designed to protect the end of the finger when sewing. Among the earliest known thimbles, dating from before AD 79, were those made of bronze and found ...
thimerosal: organic compound used as an antiseptic for the skin and mucous membranes, sometimes marketed under the trade name Merthiolate. It is related to merbromin (Mercurochrome) and nitromersol (Metaphen). Thimerosal disinfects ...
Thimphu: capital of Bhutan. The city, situated in the west-central part of the country, is in the Himalaya Mountains on the Raidak (also called Thimphu, or Wong) River at about 7,000 ...
thin-layer chromatography: in analytical chemistry, technique for separating dissolved chemical substances by virtue of their differential migration over glass plates or plastic sheets coated with a thin layer of a finely ground ...
thing: in medieval Scandinavia, the local, provincial, and, in Iceland, national assemblies of freemen that formed the fundamental unit of government and law. Meeting at fixed intervals, the things, in which ...
Thingvalla, Lake: lake, southwestern Iceland, 20 miles (32 km) east of Reykjavik. The lake is about 9 miles (14 km) long and up to 6 miles (10 km) wide and reaches a ...
Thingvellir: historical site, southwestern Iceland, on the northern shore of Thingvallavatn. From 930 to 1798 it was the annual meeting place of the Althing (Parliament). Though little remains of any of ...
thiol: any of a class of organic chemical compounds similar to the alcohols and phenols but containing a sulfur atom in place of the oxygen atom. Thiols are among the odorous ...
Thionville: town, Moselle departement, Lorraine region, northeastern France, on the canalized Moselle River, near the Luxembourg border. It has remains of a 13th-century castle, built by the counts of Luxembourg. Formerly ...
thiophene: the simplest sulfur-containing aromatic compound, with molecular formula C₄H₄S, which closely resembles benzene in its chemical and physical properties. It occurs with benzene in coal tar, from which source it ...
thiourea: an organic compound that resembles urea (q.v.) but contains sulfur instead of oxygen; i.e., the molecular formula is CS(NH₂)₂, while that of urea is CO(NH₂)₂. Like urea, it can be ...
Third Department: office created by Emperor Nicholas I (July 15 [July 3, old style], 1826) to conduct secret police operations. Designed by Count A.Kh. Benckendorff, who was also its first chief administrator ...
Third Estate: in French history, with the nobility and the clergy, one of the three orders into which members were divided in the pre-Revolutionary Estates-General (q.v.); it represented the great majority of ...
Third Reich: official Nazi designation for the regime in Germany (q.v.) from January 1933 to May 1945, as the presumed successor of the medieval and early modern Holy Roman Empire of 800 ...