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correspondence principle

(Encyclopedia)correspondence principle, physical principle, enunciated by Niels Bohr in 1923, according to which the predictions of the quantum theory must correspond to the predictions of the classical theories of...

chalcedony

(Encyclopedia)chalcedony kălsĕdˈənē [key] [from Chalcedon], form of quartz the crystals of which are so minute that its crystalline structure cannot be seen except with the aid of a microscope. Chalcedony has ...

Claude, Albert

(Encyclopedia)Claude, Albert älbârrˈ klōd [key], 1899–1983, Belgian biologist, b. Longlier, M.D., Univ. of Liège, 1928. He joined the Rockefeller Institute (now Rockefeller Univ.) in 1929 and spent his entir...

Nicol prism

(Encyclopedia)Nicol prism nĭkˈəl [key], optical device invented (1828) by William Nicol of Edinburgh. It consists essentially of a crystal of calcite, or Iceland spar, that is cut at an angle into two equal piec...

cyanobacteria

(Encyclopedia)cyanobacteria sīˌənōbăktĭrˈēə, sī-ănˌō– [key] or blue-green algae, photosynthetic bacteria that contain chlorophyll. For many years they were classified in the plant kingdom along with ...

tenrec

(Encyclopedia)tenrec tĕnˈrĕk [key], any of the small insectivorous mammals of the family Tenrecidae, also called tendrecs or tanrecs. These animals are found on the island of Madagascar. In that closed environme...

motivation

(Encyclopedia)motivation, in psychology, the intention of achieving a goal, leading to goal-directed behavior. Some human activity seems to be best explained by postulating an inner directing drive. While a drive i...

Brownian movement

(Encyclopedia)Brownian movement or motion, zigzag, irregular motion exhibited by minute particles of matter when suspended in a fluid. The effect has been observed in all types of colloidal suspensions (see colloid...

Cutler, Manasseh

(Encyclopedia)Cutler, Manasseh mənăsˈə [key], 1742–1823, American clergyman, scientist, and one of the organizers of the Ohio Company of Associates, b. Killingly, Conn. A student of both law and theology, he ...

protoplasm

(Encyclopedia)protoplasm, term once used for the fundamental material of which all living things were thought to be composed. It was studied by a number of early scientists, especially by Félix Dujardin, J. E. Pur...