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volt

(Encyclopedia)volt [for Alessandro Volta], abbr. V, unit of electric potential and electromotive force. It is defined as the difference of electric potential existing across the ends of a conductor carrying a const...

dark energy

(Encyclopedia)dark energy, repulsive force that opposes the self-attraction of matter (see gravitation) and causes the expansion of the universe to accelerate. The search for dark energy was triggered by the discov...

uncertainty principle

(Encyclopedia)uncertainty principle, physical principle, enunciated by Werner Heisenberg in 1927, that places an absolute, theoretical limit on the combined accuracy of certain pairs of simultaneous, related measur...

Dionysius the Elder

(Encyclopedia)Dionysius the Elder, c.430–367 b.c., tyrant of Syracuse. Of humble origin, he entered politics as a supporter of the poorer classes. Having prompted (400 b.c.) a measure to elect truly democratic ge...

corns and calluses

(Encyclopedia)corns and calluses, thickenings of the outer layer of skin where there is irritation or constant pressure. Corns are cone-shaped with their points protruding into the dermis, or inner layer of skin. T...

Farquhar, George

(Encyclopedia)Farquhar, George färˈkər, –kwər [key], 1678–1707, Irish dramatist, b. Londonderry (now Derry), Ireland. After his short career as an actor ended when he severely wounded a fellow actor in a st...

polynomial

(Encyclopedia)polynomial, mathematical expression which is a finite sum, each term being a constant times a product of one or more variables raised to powers. With only one variable the general form of a polynomial...

Sudd

(Encyclopedia)Sudd so͝od [key], swampy region, c.200 mi (320 km) long, and c.150 mi (240 km) wide, central South Sudan, E central Africa. It is fed by the Bahr el Jebel, the Bahr el Ghazal, and the Bahr el Arab, h...

Beer's law

(Encyclopedia)Beer's law [for August Beer], physical law stating that the quantity of light absorbed by a substance dissolved in a nonabsorbing solvent is directly proportional to the concentration of the substance...

Boltzmann, Ludwig

(Encyclopedia)Boltzmann, Ludwig lo͝otˈvĭkh bôltsˈmän [key], 1844–1906, Austrian physicist, b. Vienna, educated at Univ. of Vienna. He began teaching (1869) at Graz Univ. In 1873 he became mathematics profes...