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purine

(Encyclopedia)CE5 Purines found in deoxyribonucleic acid (DNA) purine, type of organic base found in the nucleotides and nucleic acids of plant and animal tissue. The German chemist Emil Fischer did much of the...

pyramid, in geometry

(Encyclopedia)CE5 Pyramid pyramid, in geometry, solid figure bounded by a polygon (the base, or directrix) and the surface generated by a moving line (the generator) passing through a fixed point (vertex) and c...

parabola

(Encyclopedia)CE5 Parabola parabola pərăbˈələ [key], plane curve consisting of all points equidistant from a given fixed point (focus) and a given fixed line (directrix) (see illustration). It is the conic...

hurdy-gurdy

(Encyclopedia)CE5 Hurdy-gurdy hurdy-gurdy, musical instrument with three strings that are caused to vibrate by a wooden wheel turned by a crank. Stopping is accomplished by keys that usually affect only the str...

angiosperm

(Encyclopedia)CE5 Life cycle of an angiosperm angiosperm ănˈjēəspûrmˌ [key], term denoting seed plants in which the ovules, or young seeds, are enclosed within the ovary (that part of the pistil specializ...

weather vane

(Encyclopedia)weather vane or wind vane, instrument used to indicate wind direction. It consists of an asymmetrically shaped object, e.g., an arrow or a rooster, mounted at its center of gravity so it can move free...

blue shift

(Encyclopedia)blue shift or blueshift, in astronomy, the systematic displacement of individual lines in the spectrum of a celestial object toward the blue, or shorter wavelength, end of the visible spectrum. The am...

screw

(Encyclopedia)screw, simple machine consisting essentially of a solid cylinder, usually of metal, around which an inclined plane winds spirally, either clockwise or counterclockwise. It is used to fasten one object...

zodiac

(Encyclopedia)CE5 Signs of the zodiac CEE zodiac zōˈdēăk [key] [Gr. zoion=animal], in astronomy, zone of the sky that includes about 8° on either side of the ecliptic. The apparent paths of the sun, the...

amulet

(Encyclopedia)amulet ămˈyəlĭt [key], object or formula that credulity and superstition have endowed with the power of warding off harmful influences. The use of the amulet to avert danger and to dispel evil has...