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dominoes

(Encyclopedia)dominoes, game played with a set of rectangular pieces (usually 28 in number) called dominoes. Each piece (made of wood, bone, ivory, plastic, or other material) has one blank face and one face marked...

quaternion

(Encyclopedia)quaternion kwətûrˈnēən [key], in mathematics, a type of higher complex number first suggested by Sir William R. Hamilton in 1843. A complex number is a number of the form a+bi when a and b are re...

tariff

(Encyclopedia)tariff, tax on imported and, more rarely, exported goods. It is also called a customs duty. Tariffs may be distinguished from other taxes in that their predominant purpose is not financial but economi...

Darwinism

(Encyclopedia)Darwinism, concept of evolution developed in the mid-19th cent. by Charles Robert Darwin. Darwin's meticulously documented observations led him to question the then current belief in special creation ...

psychotherapy

(Encyclopedia)psychotherapy, treatment of mental and emotional disorders using psychological methods. Psychotherapy, thus, does not include physiological interventions, such as drug therapy or electroconvulsive the...

geometric problems of antiquity

(Encyclopedia)geometric problems of antiquity, three famous problems involving elementary geometric constructions with straight edge and compass, conjectured by the ancient Greeks to be impossible but not proved to...

absolute value

(Encyclopedia)absolute value, magnitude of a number or other mathematical expression disregarding its sign; thus, the absolute value is positive, whether the original expression is positive or negative. In symbols,...

Federer, Roger

(Encyclopedia)Federer, Roger, 1981–, Swiss tennis player, b. Basel. He was an outstanding junior player, ranking number one in 1998, the year he turned pro. Federer won his first Association of Tennis Professiona...

cell, in biology

(Encyclopedia)CE5 Animal cell cell, in biology, the unit of structure and function of which all plants and animals are composed. The cell is the smallest unit in the living organism that is capable of integrati...

mechanism

(Encyclopedia)mechanism, philosophical theory about the nature of organic systems, holding that organisms are machines in the sense that they are material systems. Mechanism seeks to explain biological processes, i...