Echo In Greek mythology, a mountain nymph transformed into a disem¬ bodied voice. According to Ovid, her chatter distracted Hera from the infi¬ delities of Zeus, and the goddess punished her by depriving her of independent speech, rendering her able only to repeat the last words spo¬ ken by another. When Narcissus failed to requite her love, she faded away into a voice only.
echolocation V.e-ko-lo-'ka-shsnV Physiological process for locating distant or invisible objects (such as prey) by emitting sound waves that are reflected back to the emitter by the objects. Echolocation is used by an animal to orient itself, avoid obstacles, find food, and interact socially. Most bats employ echolocation, as do most, if not all, toothed whales (but apparently no baleen whales), a few shrews, and two kinds of birds (oil- birds and certain cave swiftlets). Echolocation pulses consist of short bursts of sound at frequencies ranging from about 1,000 Hz in birds to at least 200,000 Hz in whales. Bats use frequencies from about 30,000 to about 120,000 Hz.
Eck, Johann orig. Johann Maier (b. Nov. 13, 1486, Egg, Swabia—d. Feb. 10, 1543, Ingolstadt, Bavaria) German Roman Catholic theologian. He was ordained in 1508, became a doctor of theology in 1510, and began a lifelong career at the University of Ingolstadt. Initially friendly with Martin Luther, Eck assailed Luther’s Ninety-five Theses as heretical. In 1519 he debated Luther and Andreas Karlstadt (c. 1480- 1541), and Leo X commissioned Eck to publish and enforce the papal bull condemning the Theses. Eck’s treatise Enchiridion Against the Lutherans (1525) summarized contested Catholic beliefs, Protestant objections to them, and Catholic answers to the objections; it was Eck’s most popular work and the best-known Catholic polemical handbook of the 16th cen¬ tury.
Eckert, J(ohn) Presper, Jr. (b. April 9, 1919, Philadelphia, Pa., U.S.—d. June 3, 1995, Bryn Mawr, Pa.) U.S. engineer. He studied at the University of Pennsylvania. In 1946 he and John W. Mauchly built a digi¬ tal computer, the ENIAC, which contained a primitive form of the cir¬ cuitry used in present-day high-speed computers. In 1949 they introduced the BINAC (Binary Automatic Computer). Their third model, UNIVAC I (Universal Automatic Computer), found many uses in commerce. Eckert received 85 patents and in 1969 was awarded the National Medal of Sci¬ ence.
Eckert, Wallace J(ohn) (b. June 19, 1902, Pittsburgh, Pa., U.S.—d. Aug. 24, 1971, Englewood, N.J.) U.S. astronomer. He received his Ph.D. from Yale University. He was one of the first to apply IBM punched-card equipment to the reduction of astronomical data and to describe planetary orbits numerically. As director of Columbia University’s Watson Scien¬ tific Computing Laboratory from 1945, he used computers to determine precise planetary positions and made major contributions to the study of the orbit of the Moon, one of whose craters is named for him.
Eckhart, Meister orig. Johannes (b. c. 1260?, Hochheim?, Thuringia—d. 1327/28?, Avignon) German theologian and mystic. A Dominican from age 15, he studied theology at Cologne and Paris and became a popular preacher and teacher. In his mid 30s he served as vicar of Thuringia. His mystical writings examined the relationship between God and humanity; he pictured the soul achieving complete union with God and posited something (Godhead) beyond God. He took up a pro¬ fessorship in Cologne in his 60th year; shortly thereafter he was charged with heresy on several points in his works. He died before he could rebut a second charge.
Eckstine \ l ek-,stln\, Billy orig. William Clarence Eckstein (b.
July 8, 1914, Pittsburgh, Pa., U.S.—d. March 8, 1993, Pittsburgh) U.S.
Short-beaked echidna (Tachyglossus aculeatus).
KRISTI L BOWMAN
© 2006 Encyclopaedia Britannica, Inc.
eclampsia ► Economic Co-operation I 593
Eclipses of the Sun and Moon. A solar eclipse occurs when the Moon passes between Earth and the Sun. Observers in the Moon's penumbral shadow see a partial block¬ ing of the Sun; those in the umbra see the Sun completely covered by the Moon. A lunar eclipse occurs when the Moon passes into Earth's shadow. In the penumbra, the Moon may appear slightly dimmed; when it enters the umbra, the entire Moon becomes quite dark and may take on a reddish tinge.
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singer and bandleader. Eckstine sang with Earl Hines’s big band (1939— 43), then formed his own band in 1944. Sympathetic with the new sounds of bebop, Eckstine engaged many of its innovators, including Dizzy Gillespie, Charlie Parker, and Sarah Vaughan. Disbanding the group in 1947, he achieved greater popular success as a solo performer, specializing in bal¬ lads that featured his deep, resonant baritone. He was one of the greatest interpreters of popular song and blues in jazz.
eclampsia See preeclampsia and eclampsia
eclipse The passage of all or part of one celestial body into the shadow of another, the eclipsing body. Observers on Earth experience two major types—lunar eclipses and solar eclipses—each of which involves the Sun and the Moon. The type observed depends on whether Earth is the eclips¬ ing body or the body in shadow. In a lunar eclipse the orbit of the Moon carries it through Earth’s shadow. Observers see the full Moon dim con¬ siderably, but it remains faintly visible. In a solar eclipse the Moon is the eclipsing body, passing between Earth and the Sun while casting a trav¬ eling shadow across Earth’s lighted surface. Observers along the shad¬ ow’s path see a total or partial obscuring of the Sun’s disk by the Moon’s silhouette. The shadow cast by the eclipsing body consists of the central umbra, into which no direct sunlight penetrates (total eclipse), and the encircling penumbra, reached by light from only part of the Sun’s disk (partial eclipse). Solar eclipses visible from different parts of Earth occur two to five times a year; one total solar eclipse occurs in most years. When Earth is closest to the Sun and the Moon farthest from Earth, the Moon’s silhouette may fall entirely within the Sun’s disk, with a ring of the disk visible around it (annular eclipse). Lunar eclipses occur twice in most years. Other kinds of eclipses include those of the Sun by Mercury or Venus (transits), of distant stars by planets or planetary satellites (occul- tations), and of stars by orbiting companion stars (see eclipsing variable star). See also Baily's beads. See illustration above.
eclipsing variable star or eclipsing binary Binary star in an orbit whose plane passes through or very near Earth. An observer on Earth sees one star pass periodically in front of the other and diminish its light through an eclipse. The star Algol, in the constellation Perseus, was the first such star recognized (1782); thousands are now known. By combin¬ ing the brightness variations with spectroscopic information for both stars, astronomers can determine the mass and size of each star. See also vari¬ able STAR.
ecliptic \i-‘klip-tik\ Great circle that is the apparent path of the Sun among the constellations in the course of a year; from another viewpoint, the projection on the celestial sphere of the orbit of Earth around the Sun, which intersects the plane of the celestial equator at the vernal and autum¬ nal EQUiNOXes. The constellations of the zodiac are arranged along the ecliptic.
eclogite Vek-l3-jlt\ Any member of metamorphic rocks whose original composition is similar to that of basalt. Eclogites consist primarily of green pyroxene (omphacite) and red garnet (pyrope), with small amounts of various other minerals such as kyanite and rutile. These minerals in the eclogite are the result of reactions in originally igneous minerals having been subjected to extremely high pressures and moderate to relatively high temperatures.
eclogue Vek-.log, 'ek-,lag\ Short, usually pastoral, poem in the form of a dialogue or soliloquy (see pastoral). The eclogue as a pastoral form first