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mirror

(Encyclopedia)mirror, in optics, a reflecting surface that forms an image of an object when light rays coming from that object fall upon it (see reflection). Usually mirrors are made of plate glass, one side of whi...

carbon dioxide

(Encyclopedia)carbon dioxide, chemical compound, CO2, a colorless, odorless, tasteless gas that is about one and one-half times as dense as air under ordinary conditions of temperature and pressure. It does not bur...

chlorofluorocarbons

(Encyclopedia)chlorofluorocarbons klōrˌəflo͝orˈəkärˌbənz, klôrˌ– [key] (CFCs), organic compounds that contain carbon, chlorine, and fluorine atoms. CFCs are highly effective refrigerants that were deve...

cloud

(Encyclopedia)CE5 Approximate heights of some types of clouds cloud, aggregation of minute particles of water or ice suspended in the air. Cloudiness (or proportion of the sky covered by any form of cloud),...

polyp and medusa

(Encyclopedia)CE5 Polyp and medusa stages in the life cycle of Obelia, representative of the phylum Cnidaria polyp and medusa, names for the two body forms, one nonmotile and one typically free swimming, found ...

lung cancer

(Encyclopedia)lung cancer, cancer that originates in the tissues of the lungs. Lung cancer is the leading cause of cancer death in the United States in both men and women. Like other cancers, lung cancer occurs aft...

Progressive party

(Encyclopedia)Progressive party, in U.S. history, the name of three political organizations, active, respectively, in the presidential elections of 1912, 1924, and 1948. At Philadelphia in July, 1948, a new...

Polk, James Knox

(Encyclopedia)Polk, James Knox pōk [key], 1795–1849, 11th President of the United States (1845–49), b. Mecklenburg co., N.C. To the surprise of many, the new President proved to be his own man; he even ignor...

lead, chemical element

(Encyclopedia)lead, metallic chemical element; symbol Pb [Lat. plumbum]; at. no. 82; at. wt. 207.2; m.p. 327.502℃; b.p. about 1,740℃; sp. gr. 11.35 at 20℃; valence +2 or +4. One of the oldest metals used by h...

sewerage

(Encyclopedia)sewerage, system for the removal and disposal of chiefly liquid wastes and of rainwater, which are collectively called sewage. The average person in the industrialized world produces between 60 and 14...