D-Day, in World War II, June 6, 1944, the day Allied troops landed in Normandy, France, thus launching the last major campaign in Western Europe, under the command of General Eisenhower.
21st Century Webster's Family Encyclopedia - Davis, Henry Gassaway to Diamond
Détente (French, “relaxation”), name given to the policy of easing tensions between the United States and the USSR that occurred in the late 1960s and 1970s.
Davis Cup, international men's tennis trophy, first contested in 1900.
Davis, Henry Gassaway (1823–1916), U.S. politician; U.S. senator from West Virginia 1871–83.
Davis, Jefferson (1808–89), president of the Confederate States of America during the Civil War.
Davis, John (c. 1550–1605), English navigator and early Arctic explorer.
Davis, John William (1873–1955), U.S. politician and Democratic presidential candidate in 1924, losing to Calvin Coolidge.
Davis, Miles Dewey (1926–91), U.S. jazz musician, one of the pioneers of “bebop” in the 1940s and of “cool” jazz, with its restrained, clear sounds, in the 1950s.
Davis, Paulina Wright (1813–76), U.S. social reformer who worked for women's rights, campaigning in the 1840s against property laws that made a man the owner of his wife's possessions.
Davis, Richard Harding (1864–1916), U.S. writer, journalist, and war correspondent.
Davis, Samuel (1842–63), Confederate spy, hanged by Union troops for refusing to reveal the source of his information.
Davis Strait See: Northwest Passage.
Davis, Stuart (1894–1964), U.S. abstract painter, illustrator, and lithographer.
Davy, Sir Humphry (1778–1829), English chemist who pioneered the study of electrochemistry.
Dawes Act See: Native Americans.
Dawes, Charles Gates (1865–1951), U.S. politician who shared the 1925 Nobel Peace Prize for the plan named after him.
Dawes Plan, program presented by Charles Gates Dawes in 1924 to enable Germany to pay off World War I reparations by means of an international loan and mortgages on German industry and railways.
Day, 24-hour period during which the earth completes one rotation on its axis as it rotates around the sun.
Day of Atonement See: Yom Kippur.
Day, Clarence (1874–1935), U.S. writer of essays, sketches, reviews, and stories.
Day, Dorothy (1897–1980), U.S. social activist.
Day-Lewis, Cecil (1904–72), English author.
Day lily, any of several plants (genus Hemerocallis) of the lily family, growing 3–5 ft (91–150 cm) high.
Dayaks See: Dyak.
Dayan, Moshe (1915–81), Israeli military and political leader.
Dayfly See: Mayfly.
Daylight saving time, method of making better use of daylight by setting clocks 1 hour ahead of standard time.
Dayton (pop. 951,270), city in southwestern Ohio, seat of Montgomery County.
Dayton, Jonathan (1760–1824), U.S. soldier and politician, youngest signer of the Constitution (1787).
Daytona Beach (pop. 370,712), city in northeastern Florida, 90 mi (145 km) southeast of Jacksonville.
DC See: Electric current.
DDT (dichloro-diphenyl-trichloroethane), powerful insecticide.
De Angeli, Marguerite Lofft (1889– ), U.S. author and illustrator of children's books.
De Broglie, Prince Louis Victor (1892–1987), French physicist who received the 1929 Nobel Prize in physics for his discovery that the behavior of electrons, like that of light, could be explained in terms of wave motion.
De facto segregation See: Segregation.
De Falla, Manuel See: Falla, Manuel de.
De Forest, Lee (1873–1961), U.S. inventor of the triode (1906), an electron tube with three electrodes that could operate as a signal amplifier as well as a rectifier.
De Gasperi, Alcide (1881–1954), Italian statesman.
De Gaulle, Charles (1890–1970), French soldier and political leader, president 1945–46 and 1958–69.
De Groot, Hugo See: Grotius, Hugo.
De jure segregation See: Segregation.
Deák, Ferenc (1803–76), Hungarian statesman who negotiated the 1867 Compromise that gave Hungary internal autonomy within Austria-Hungary.
De Kooning, Willem (1904– ), Dutch-born U.S. painter, among the founders of abstract expressionism.
De la Madrid Hurtado, Miguel (1934– ), Mexican political leader.
De La Mare, Walter John (1873–1956), English poet and novelist.
De la Roche, Mazo (1879–1961), Canadian writer best known for a series of 16 novels that chronicle the Whiteoak family from 1852 to 1954.
De León, Juan Ponce See: Ponce de León, Juan.
De Lesseps, Ferdinand Marie (1805–94), French engineer and diplomat, builder of the Suez Canal.
De Maupassant, Guy (1850–93), French writer noted for his short stories.
De Mille, Agnes George (1909–93), U.S. dancer and choreographer; niece of Cecil B.
De Mille, Cecil Blount (1881–1959), U.S. motion picture producer and director, noted for his use of spectacle; uncle of Agnes George De Mille.
De Molay, Order of, international organization of boys and young men between the ages of 13 and 21.
De Quincey, Thomas (1785–1859), English essayist and critic, author of Confessions of an English Opium Eater (1822), which established his literary reputation.
De Sica, Vittorio (1901–74), Italian film director.
De Sitter, Willem (1872–1934), Dutch astronomer and cosmologist who examined the age, size, and structure of the universe.
De Smet, Pierre Jean (1801–73), Jesuit missionary to the North American Indians.
De Soto, Hernando (1500?–42), Spanish explorer, discoverer of the Mississippi River.
De Sucre, Antonio José See: Sucre, Antonio José de.
De Tocqueville, Alexis See: Tocqueville, Alexis de.
De Valera, Eamon (1882–1975), Irish statesman; prime minister 1932–48, 1951–54, and 1957–58; and president of Ireland 1959–73.
De Valois, Dame Ninette (Edris Stanus; 1898– ), Irish dancer and choreographer.
De Voto, Bernard Augustine (1897–1955), U.S. journalist and author.
De Vries, Hugo (1848–1935), Dutch botanist who developed the theory of mutation, suggesting that new plant and animal species are the result of sudden transformations that occur spontaneously and are continued for generations.
De Witt, Jan (1625–72), Dutch statesman.
DEA See: Drug Enforcement Administration.
Deacon (Greek diakonos, “servant”), assistant to the clergy in a Christian church.
Dead Sea, salt lake in the Great Rift Valley, on the Israel-Jordan border.
Dead Sea Scrolls, group of Hebrew and Aramaic manuscripts discovered in caves near the northwestern coast of the Dead Sea in 1947 and later.
Deadly nightshade See: Belladonna.
Deadwood (pop. 1,830), city in the Black Hills of South Dakota; the seat of Lawrence County.
Deafness, partial or total impairment of the sense of hearing.
Dean, Dizzy (Jay Hanna Dean; 1911–74), U.S. baseball pitcher.
Dean, James (1931–55), U.S. actor.
Deane, Silas (1737–89), U.S. diplomat and first envoy to Europe.
Dearborn (pop. 89,286), city in southeast Michigan, on the River Rouge 10 mi (16 km) west of Detroit.
Dearborn, Henry (1751–1829), U.S. soldier and politician.
Death, complete and irreversible cessation of life in an organism or part of an organism. The moment of death is conventionally accepted as the time when the heart ceases to beat, there is no breathing, and the brain shows no evidence of function. Since it is possible to resuscitate and maintain heart function and to take over breathing mechanically, the brain may suffer irreversible death while &…
Death penalty See: Capital punishment.
Death's-head moth, large moth (Acherontia atropos) of the family Sphingidae.
Death Valley, arid valley in southeast California and southern Nevada.
Deathwatch, any of several beetles belonging to the family Anobiidae.
DeBakey, Michael Ellis (1908– ), U.S. heart surgeon who developed the pump for the heart-lung machine (1932), devised a new surgical procedure to treat aneurysm, and successfully implanted a mechanical device to help restore a diseased heart (1967).
Debate, formal and regulated discussion of a given proposition.
Deborah, prophet and judge in the Old Testament.
Debrecen (pop. 214,700), city in Hungary, 120 m (193 km) east of Budapest.
Debs, Eugene Victor (1855–1926), U.S. labor organizer and socialist political leader.
Debt, something owed, whether money, services, or goods.
Debussy, Claude Achille (1862–1918), French composer.
Debye, Peter Joseph William (1884–1966), Dutch physical chemist chiefly known for the Debye-Hückel theory of ionic solution (1923).
Decalogue See: Ten Commandments.
Decameron, The, collection of 100 stories (written 1348–53) by the Italian author Giovanni Boccaccio.
Decathlon, 10-event track-and-field contest consisting of the 100-meter dash; the 400-meter and 1,500-meter flat races; the 110-meter hurdle race; pole vaulting; discus throwing; shot putting; javelin throwing; and the broad and high jumps.
Decatur (pop. 117,206), city in central Illinois located on the Sangamon River and named after the U.S. naval officer Stephen Decatur.
Decatur, Stephen (1779–1820), U.S. naval hero.
Decembrist revolt, unsuccessful uprising against the tsarist government in Russia organized by army officers in December 1825.
Decemvirs See: Twelve Tables, Laws of the.
Decibel (dB), measurement of sound intensity; one-tenth of a bel.
Deciduous tree, any of those trees that shed their leaves each year, usually in the fall.
Decimal system, system of computation based on the number 10 (Latin decem). Almost all countries use the decimal system. The system uses 10 numerals — 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9 — to represent any number as the sum of powers of 10. The units place indicates multiples of 100 (defined as 1), the tens place indicates multiples of 101, the hundreds place indicates multiples of 102, …
Declaration of Independence, document in which representatives of the 13 American colonies set forth the reasons for their break with Britain. July 4, the day in 1776 on which the Continental Congress adopted the Declaration of Independence, is observed as Independence Day, a U.S. national holiday. A royal proclamation of Aug. 1775 held the colonies to be in a state of rebellion, and in Nov. the B…
Declaration of the Rights of Man and the Citizen, key philosophical document of the French Revolution, adopted by the National Assembly on August 26, 1789.
Declaratory Act See: Revolutionary War in America.
Declination, in astronomy, one of two coordinates used to specify the position of an object in the sky under the equatorial coordinate system.
Decode, in information science, the translation or determination of the meaning of a coded set of data.
Decomposition, chemical, reduction of a compound to simpler substances, or to its elemental components.
Decompression sickness See: Bends.
Decoration Day See: Memorial Day.
Decorations, medals, and orders, awards acknowledging exceptional civil or military service, acts of bravery, and notable achievements in the arts and sciences. In the United States the highest civil decoration is the Presidential Medal of Freedom; the Medal for Merit is also a civil decoration for outstanding services. The highest military decoration “for conspicuous gallantry at the risk …
Decorative arts, term covering a variety of artistic activities (including woodworking, glass handicrafts, textiles, and metalworking) not traditionally included in the fine arts, which include painting, sculpture, and architecture.
Decoupage (from French découper, “to cut out”), decorative art form in which paper shapes are glued onto other items and covered with coats of varnish.
Deductive method, the process of reasoning by which conclusions are drawn by logical inference from given premises.
Dee, John (1527–1628), English philosopher and mathematician accused of sorcery against Queen Mary.
Deed, legal document transferring the ownership of property.
Deep, ocean area with a depth in excess of 18,000 ft (5,490 m).
Deer, any of about 40 species of cloven-hoofed mammals of the family Cervidae, found in Europe, Asia, and the Americas.
Deer fly, insect belonging to the horsefly family, found throughout North America.
Deere, John (1804–86), U.S. inventor who developed and marketed the first steel plows.
Deerhound, Scottish breed of dog skilled at hunting deer by sight.
Defenestration of Prague See: Thirty Years' War.
Defense, Department of, executive department of the U.S. government responsible for the recruitment, training, organization, and operation of the armed forces. The National Security Act of 1947 superseded the War Department and brought the previously separate departments of the Army, Navy, and Air Force into the National Military Establishment, which was renamed the Department of Defense in 1949. …
Defense mechanism, term in psychoanalysis referring to involuntary or unconscious measures adopted by individuals to protect themselves against painful emotions associated with some disagreeable physical or mental situation of frequent occurrence.
Defoe, Daniel (1660?–1731), English author, one of the originators of the English novel.
Degas, (Hilaire Germain) Edgar (1834–1917), French painter and sculptor associated with impressionism.
Degree, academic, title conferred by a university as a recognition of academic competence. Degrees were originally awarded after the candidate had successfully passed a vigorous oral examination, but abuse of this system (particularly in the 18th century at Oxford and Cambridge) led to the gradual adoption of the written examination, at least for the lower (bachelor) degrees. Master's and d…
Dehydrated food, food that has been preserved by drying.
Dehydration, removal of water from substances, usually as part of an industrial process or in the preservation of food. Water may be removed in drying chambers through which hot air or gases are passed. A vacuum may be used instead of hot air or gas to evaporate the water at lower temperatures. In chemical processes, gases are dried by passing them through tubes containing drying agents such as ca…
Deism, religious system developed in the 17th and 18th centuries and championed by such thinkers as Voltaire and Jean Jacques Rousseau.
Dekker, Thomas (c. 1570–c.1632), English dramatist and pamphleteer.
Del Cano, Juan Sebastián See: Magellan, Ferdinand.
Delacroix, Ferdinand – Victor – Eugène (1798–1863), French painter whose themes are typical of Romanticism.
Delany, Martin Robinson (1812–85), African-American journalist, physician, and army officer.
Delaunay, Robert (1885–1941), French abstract painter.
Delaware, Native American tribe of the Algonquian linguistic group that lived in the Delaware River basin area until driven into Ohio in the 18th century by the incursions of colonists and the violence of the French and Indian Wars.
Delaware, one of the mid-Atlantic states of the United States; bordered by Maryland in the west and south, Pennsylvania in the north, and the Delaware Bay in the east. Delaware is located on the Delmarva Peninsula, along with parts of Maryland and Virginia. Almost all of the state is part of the Atlantic Coastal Plain, which stretches from New Jersey to southern Florida. Delaware's mean ele…
Delaware Bay, inlet of the Atlantic Ocean, bounded by New Jersey on the north and Delaware on the south and west.
Delaware River, major waterway (about 410 mi/660 km long) in the eastern United States.
Delbrück, Max (1906–61), German-born U.S. biologist whose discovery of a method for detecting and measuring the rate of mutations in bacteria opened up the study of bacterial genetics.
Delgado, José Matías (1767–1832), Salvadoran priest and patriot.
Delhi (pop. 7,206,700), city in northern India, on a plain that has always been strategically important for control of the whole Indian subcontinent.
Delhi sultanate, first Muslim empire in India (1192–1398).
Delian League, confederacy of Greek states formed by Athens in 478 B.C. to follow up the Hellenic League's victories against Persia.
Delibes, (Clément Philibert) Léo (1836–91), French composer.
Delilah, Samson's Philistine mistress in the Old Testament.
Delinquency, juvenile See: Juvenile delinquency.
Delirium tremens, specific condition of confusion, violent shaking, fever, and hallucinations caused by alcohol withdrawal.
Delius, Frederick (1862–1934), English composer.
Della Francesca, Piero See: Piero della Francesca.
Della Robbia, Luca (1399?–1482), Italian Renaissance sculptor and ceramicist known for his glazed terra cottas.
Dells See: Dalles.
Deloria, Vine, Jr. (1933– ), Native American leader.
Delphi, Greek town located on the lower slopes of Mt.
Delphinium See: Flower; Larkspur.
Delta, alluvial plain at the mouth of a river, often projecting into a sea or lake and crossed by many water channels.
Deluge, in biblical tradition, great flood sent by God to punish humanity, described in Genesis 6–8.
Demand See: Supply and demand.
Demarcation, Line of See: Line of Demarcation.
Demeter, in Greek mythology, the goddess of grain, agriculture, harvest, and fertility.
Democracy, system of government under which all members of society have a say in making political decisions, either directly or indirectly. Direct democracy, in which political decisions are made by citizens meeting together, has generally been superceded by representative democracy, under which the population elects members of a decision-making body. Historically, the portion of the population pe…
Democratic-Farmer-Labor Party See: Farmer-Labor Party.
Democratic Party, one of the 2 major political parties in the United States. Democrats trace their history back to the Democratic Republican Party (1792) of Thomas Jefferson, who favored popular control of the government. Following the presidential inauguration of Andrew Jackson in 1828, the Democratic Party's base was broadened, with representation from the new West as well as the East. Ja…
Democratic-Republican Party, one of the two political parties founded during the first decades of the United States.
Democritus (460?–370? B.C.), Greek philosopher who theorized that reality is separated into atoms and the void.
Demography, study of the distribution, composition, and changes of human populations.
Demosthenes (384–322 B.C.), Athenian orator and speech writer, best known for his attempts to rouse Athens to resist the encroachment of Philip of Macedon, the father of Alexander the Great.
Dempsey, Jack (William Harrison Dempsey; 1895–1983), U.S. boxer.
Dempster, Arthur Jeffrey (1886–1950), U.S. physicist, developer of the first mass spectrometer (1918), an instrument that measures the mass of atomic nuclei, thereby providing a way to analyze chemical compositions and to distinguish isotopes.
Demuth, Charles (1883–1935), U.S. watercolorist and illustrator.
Dendrochronology, dating of past events by the study of tree rings.
Deneb, or Alpha Cygni, blue-white star, brightest star in the constellation Cygnus and one of the brightest in the sky.
Deng Xiaoping (1904–97), Chinese Communist leader.
Dengue, or breakbone fever, infectious disease characterized by sudden onset of headache, fever, prostration, severe joint and muscle pain, and swollen glands.
Denmark, country in northwest Europe consisting of the Jutland Peninsula and 483 islands, of which about 100 are inhabited. The Faeroe Islands, north of Scotland, form a self-governing community within the Kingdom of Denmark; Greenland, the largest island in the world, is a former Danish county that received Home Rule on May 1, 1979. The Jutland Peninsula contains the country's only land fr…
Denominator See: Fraction.
Density, ratio of mass of a substance to its volume.
Dental hygiene, study and practice of techniques designed to maintain good oral health.
Dentistry, profession that deals with the diagnosis, prevention, and treatment of malformations and diseases affecting the teeth and their related structures, such as gums and oral bones.
Denver (pop. 513,500), capital and largest city of Colorado, situated in the Rocky Mountains foothills, a mile above sea level.
Deoxyribonucleic Acid See: DNA.
Department of , Departments of the U.S. government are listed under the key word; for example: Education, U.S.
Depreciation, loss in the value of an asset brought about by age, use, or both.
Depressant, any of various drugs that slow physical, mental, or emotional activity.
Depression, in economics, major decline in business activity involving sharp reductions in industrial production, a rise in bankruptcies, increased unemployment, and a general loss of business confidence.
Depression, emotional state characterized by sadness, despondency, apathy, and sometimes a deep sense of loss; in psychiatry, clinical depressive illness is more intense and lasts longer than common depressed feelings. Seriously depressed people feel isolated and hopeless and often reproach or blame themselves for exaggerated faults and shortcomings. Fatigue and disturbed sleep are common, while s…
Depth charge, explosive weapon used against submarines and other submerged targets.
Derain, André (1880–1954), French painter, one of the original fauves.
Derby, annual horse race begun at Epsom, England, in 1780 by the 12th earl of Derby.
Derby, Kentucky See: Kentucky Derby.
Dermaptera See: Earwig.
Dermatitis, inflammation of the skin, accompanied by moderate to severe itching, with redness, swelling, and sometimes blisters.
Dermatology, subspeciality of medicine concerned with the diagnosis and treatment of skin diseases: alargely visual speciality, but aided by skin biopsy in certain instances.
Dermis, or corium, the inner layer of skin beneath the epidermis.
Dervish, Muslim mystic, member of a Sufi brotherhood.
DES (diethylstilbestrol), synthetic hormone having the properties of estrogen, the main female sex hormone.
Des Moines (pop. 196,000), capital and largest city of Iowa.
Desai, Morarji (1896–1995), Indian political leader.
Desalination See: Water.
Descartes, René (1596–1650), French mathematician, scientist, and philosopher, often referred to as “the father of modern philosophy.” A dualist who believed the world was composed of 2 basic substances (matter and spirit), he ignored accepted scholastic philosophy and stated a person should doubt all sense experiences; but if a person can think and doubt, he or she therefore exists.
Deschutes River See: Oregon.
Desegregation See: Segregation.
Desert, dry region where life has extreme difficulty surviving.
Desert Shield, Operation See: Persian Gulf War.
Desert Storm, Operation See: Persian Gulf War.
Desertion, in military law, the abandonment by a soldier of his or her post without the intention of returning.
Design, purposeful arrangement of the elements in a creative work or process.
Despotism, absolute government by one person who rules without any constitutional controls.
Desprez, Josquin (1440?–1521), Flemish composer who wrote both secular and sacred music for voice.
Dessalines, Jean Jacques (1758–1806), first black ruler of Haiti.
Destouches, Henri-Louis See: Céline, Louis-Ferdinand.
Destroyer, small, fast naval warship that evolved in the 1890s out of British torpedo boats.
Detective story, popular form of fiction in which a detective solves a crime, usually a murder, by discovering and interpreting clues.
Detergent, synthetic chemical that has the same cleaning action as soap but does not form a scum when used in hard water.
Determinism, philosophical theory that all events are determined (inescapably caused) by preexisting events that, when considered in the context of inviolable physical laws, completely account for the subsequent events.
Detonator, device used to set off a high-explosive charge.
Detroit (pop. 1,012,100), Michigan, fifth-largest city in the United States, often called the “Motor City” because it produces over a quarter of all the nation's cars and trucks.
Detroit River, river flowing about 30 mi (48 km) from Lake St.
Deucalion, in Greek mythology, son of the Titan Prometheus.
Deuterium, or heavy hydrogen (D or H2), isotope of hydrogen in which the atomic nucleus contains a neutron as well as a proton, giving it an atomic weight of approximately 2.
Deuteron See: Deuterium.
Deuteronomy, fifth book of the Old Testament and last book of the Pentateuch.
Deutschland über Alles, or “Germany Above All Else,” the German national anthem from 1922 until the division of Germany after World War II.
Deutzia, genus of shrubs having clusters of white, pink, or purple, 5-pet-alled flowers and serated, fuzzy leaves.
Devaluation, reduction of the official value of a currency, the opposite of revaluation.
Developing country, term used for any nation with a weak industrial base, a low per capita income, and low gross national product.
Developmental psychology, study of behavioral changes that occur during the years from birth to early childhood.
Devil, in Western religions and sects, chief spirit of evil and commander of lesser evil spirits or demons.
Devil's Island, small island off the coast of French Guiana, the site of a French penal colony (1852–1951) for political prisoners, among them Alfred Dreyfus.
Devil's paintbrush, plant with orange-red flowers on a leafless stem up to 28 in (71 cm) long, with oblong leaves growing from the base.
Devil's Triangle See: Bermuda Triangle.
Devil worship, worship of Satan, demons, or evil spirits.
Devolution, War of (1667–68), conflict between Spain and France over the right of succession to the Spanish Netherlands.
Devonian Period, fourth period of the Paleozoic Era, beginning about 400 million years ago and lasting 55 million years.
Dew, layer of water droplets that forms at night on or near the ground.
Dew line, acronym for Distant Early Warning line, consisting of 31 radar tracking stations between Alaska and Greenland designed to watch for Soviet air attacks.
Dew point, air temperature at which water vapor turns to liquid.
Dewberry, trailing bramble (genus Rubus) with blackberry-like fruit, the only U.S. member of the blackberry group that is cultivated.
Dewey decimal system, devised by Melvil Dewey (1851–1931) for classification of books in libraries, based on the decimal system of numbers.
Dewey, George (1837–1917), U.S. naval hero promoted to admiral of the navy (the highest rank) for his victory at the Battle of Manila Bay and the capture of the Philippines from Spain.
Dewey, John (1859–1952), U.S. philosopher and educator.
Dewey, Melvil (1851–1931), U.S. librarian, inventor of the scheme for organizing library collections known as the Dewey decimal classification system.
Dewey, Thomas Edmund (1902–71), U.S. lawyer and politician.
Dextrin, chemical substance formed when starch is broken down by the body during digestion.
Dextrose, chemical name for pure glucose sugar.
Dhaka (formerly Dacca; pop. 3,637,900), capital of the independent state of Bangladesh (formerly East Pakistan).
Dharma, concept of the eternal truth or law in Hinduism, Buddhism, and Jainism.
Diabetes, or diabetes mellitus, disease characterized by the absence or inadequate secretion of insulin. Normally, sugars and starches (carbohydrates) in food are processed by digestive juices into a form of sugar called glucose, or blood sugar, which is the fuel used by the body. Insulin, a hormone produced by the pancreas, is a major regulator of this process. In the diabetic individual, either …
Diaghilev, Sergei Pavlovich (1872–1929), Russian impresario and founder (Paris, 1909) of the Ballets Russes, which inaugurated modern ballet.
Dialectic See: Hegel, Georg Wilhelm Friedrich.
Dialectical materialism See: Materialism; Philosophy.
Dialysis machine See: Kidney.
Diamond, mineral allotrope (molecular form) of carbon forming colorless cubic crystals (the other forms being graphite and the recently discovered fullerene). Diamond is the hardest known substance, with a Mohs hardness of 10, which varies slightly with the orientation of the crystal. Thus diamonds can be cut only by other diamonds. They do not conduct electricity, but conduct heat extremely well.…