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hummingbird

(Encyclopedia)hummingbird, common name for members of the family Trochilidae, small, strictly New World birds, related to the swifts, and found chiefly in the mountains of South America. Hummingbirds vary in size f...

Dyson, Freeman John

(Encyclopedia)Dyson, Freeman John dīˈsən [key], 1923–2020, British-American theoretical physicist and mathematician, studied Trinity College, Cambridge (B.A., 1945) and Cornell. He did bomber operations resear...

dream

(Encyclopedia)dream, mental activity associated with the rapid-eye-movement (REM) period of sleep. It is commonly made up of a number of visual images, scenes or thoughts expressed in terms of seeing rather than in...

chain

(Encyclopedia)chain, flexible series of connected links used in various ways, especially for the transmission of motive power, for hoisting (see pulley), and for securing or fastening. Commonly, mechanical energy f...

Pennebaker, D. A.

(Encyclopedia)Pennebaker, D. A. (Donn Alan Pennebaker), 1925–2019, pioneering documentary filmmaker, b. Evanston, Ill. His first film, Daybreak Express (1958), is a five-minute short detailing New York's doomed T...

polonium

(Encyclopedia)polonium pəlōˈnēəm [key], radioactive chemical element; symbol Po; at. no. 84; mass no. of most stable isotope 209; m.p. 254℃; b.p. 962℃; sp. gr. about 9.4; valence +2 or +4. Polonium is an e...

phosphate

(Encyclopedia)phosphate, salt or ester of phosphoric acid, H3PO4. Because phosphoric acid is tribasic (having three replaceable hydrogen atoms), it forms monophosphate, diphosphate, and triphosphate salts in which ...

Rousseff, Dilma

(Encyclopedia)Rousseff, Dilma jēlˈmä ro͞oˈsĕf [key], 1947–, Brazilian political leader, b. Belo Horizonte. The daughter of a Bulgarian immigrant lawyer and a Brazilian teacher, she was trained as an economi...

thymine

(Encyclopedia)thymine thīˈmēn [key], organic base of the pyrimidine family. Thymine was the first pyrimidine to be purified from a natural source, having been isolated from calf thymus and beef spleen in 1893–...

toxic waste

(Encyclopedia)toxic waste is waste material, often in chemical form, that can cause death or injury to living creatures. It usually is the product of industry or commerce, but comes also from residential use, agric...