Licensed from Columbia University Press
Licensed from Columbia University Press
Licensed from Columbia University Press
Licensed from Columbia University Press
Licensed from Columbia University Press
Licensed from Columbia University Press
Any of a class of highly stable organic compounds prepared by the reaction of chlorine with biphenyl, a two-ring compound. The commercial product, a mix of several PCB isomers, is a colourless, viscous liquid that is almost insoluble in water, does not degrade under high temperatures, and is a good electrical insulator (see dielectric). PCBs became widely used as lubricants, heat-transfer fluids, and fire-resistant dielectric fluids in transformers and capacitors in the 1930s and '40s. In the mid 1970s they were found to cause liver dysfunction in humans and came under suspicion as carcinogens; their manufacture and use were consequently restricted in the U.S. and many other countries, though illegal dumping by manufacturers continued. They persist in the environment and have entered the food chain, causing great harm especially to invertebrates and fish.
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Primarily in Western religions, any of numerous benevolent spiritual beings who mediate between heaven and earth. They often serve as messengers or servants of God or as guardians of an individual or nation. In Zoroastrianism the amesha spenta are arranged in a hierarchy of seven. Judaism and Christianity base their notion of angels on references in the Hebrew scriptures to divine servants and to the heavenly hosts. Two archangels (Michael and Gabriel) are mentioned in the Old Testament and two others (Raphael and Uriel) in the Apocrypha. Angels are mentioned throughout the Christian scriptures, and Christian tradition identifies nine orders of angels. Islam's hierarchy of angels descends from the four throne bearers of God to the cherubim who praise God, the four archangels, and lesser angels such as the hsubdotafazsubdotah (guardian angels). Seealso cherub; seraph.
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Angel Falls (Salto Ángel), La Gran Sabana region of Bolívar state, Venezuela.
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