DAMP

damp, a common teutonic word, meaning vapour or mist (cf. ger. _dampf_, steam), and hence moisture. in its primitive sense the word persists in the vocabulary of coal-miners. their "firedamp" (formerly fulminating damp) is marsh gas, which, when mixed with air and exploded, produced "choke damp," "after damp," or "suffocating damp" (carbon dioxide). "black damp" consists of accumulations of irrespirable gases, mostly nitrogen, which cause the lights to burn dimly, and the term "white damp" is sometimes applied to carbon monoxide. as a verb, the word means to stifle or check; hence damped vibrations or oscillations are those which have been reduced or stopped, instead of being allowed to die out naturally; the "dampers" of the piano are small pieces of felt-covered wood which fall upon the strings and stop their vibrations as the keys are allowed to rise; and the "damper" of a chimney or flue, by restricting the draught, lessens the rate of combustion.