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thunder

(Encyclopedia)thunder, sound produced along a path of a lightning flash, caused by the rapid heating and expansion of the adjacent air; lightning can heat air to temperatures as much as five times hotter than those...

foehn

(Encyclopedia)foehn fān, Ger. fön [key], warm, dry wind that occurs on the leeward slopes of a ridge of mountains. The term was originally applied to a wind of the Alps but is now used as a generic term for all w...

missal

(Encyclopedia)missal [Lat.,=of the mass], in the Roman Catholic Church, liturgical book containing all directions and texts necessary for the performance of Mass throughout the year. The Roman Missal (Missale Roman...

Mach's principle

(Encyclopedia)Mach's principle mäks [key] [for E. Mach], assertion that the inertial effects of mass are not innate in a body, but arise from its relation to the totality of all other masses, i.e., to the universe...

tachyon

(Encyclopedia)tachyon tăkˈēŏnˌ [key], hypothetical elementary particle that travels only at speeds exceeding that of light. According to the theory of relativity, the speed of light is the limiting velocity fo...

requiem

(Encyclopedia)requiem rĕkˈwēəm, rēˈ–, rāˈ– [key] [Lat.,=rest], proper Mass for the souls of the dead, performed on All Souls' Day and at funerals. The reformation of Roman Catholic liturgy following the...

jet propulsion

(Encyclopedia)CE5 Types of jet engines: In the propeller-driven turbine a stream of high-velocity gases provides the power to drive the turbine and turn the propeller. In the jet-driven turbine the stream of gas...

cyclone

(Encyclopedia)cyclone, atmospheric pressure distribution in which there is a low central pressure relative to the surrounding pressure. The resulting pressure gradient, combined with the Coriolis effect, causes air...

smoke

(Encyclopedia)smoke, visible gaseous product of incomplete combustion. Smoke varies with its source, but it usually comprises hot gas and suspended particles of carbon and tarry substances, or soot. To reduce the a...

Clark, Alvan

(Encyclopedia)Clark, Alvan, 1804–87, American astronomer and maker of astronomical lenses, b. Ashfield, Mass. In 1846 the firm of Alvan Clark & Sons was established at Cambridgeport, Mass.; it became famous a...