CHIMNEY (Fr. client i 11T,. cantina t a, fireplace, from Lat. ramians, hearth, from (;k. Kii,(uvos, bit/11110R, °Veil. furnace). A vertical structure of stone, brick, or metal, containing an internal passageway or flue through which the :mike and waste gases of eombostion are carried off from a furnace, fireplace, stove, etc.
Chimneys also periorm the important function of supplying draught to the tire from which they receive the smoke ..nd waste gases. The actiiia of the chimney depends upon the simple prin ciple that a column of ln•ated air is lighter than a cooler column of equal m•ight ; when therefore a tine full of heated air communieates freely by the lower part with the cooler air around it. the greater weight of the latter pushes the warm air upward, and thus an ascending current is produced. Other conditions being equal, the draught of a ehimuev will vary as the square root. of the height. The straighter and more per pendicula• t he chimney, the stronger will he the dradght, because the friction of the ascending current will he less, and the enoling effect of a long and tortuous course will lie saved. The maximum efficiency of a given chimney is at tained when all the air that passes up it enters by the bottom of the fire. In this ease, its tem perature is raised to the uttermost by passing, through the whole of the fire, and the lire is at the same time urged to increased combustion by the blast thus obtained. A powerful furnace may be constructed by connecting a suitable fire place, capable of being closed all round excepting at the bottom, with a tall chimney: and the amount of draught may be regulated by in ereasing or diminishing the aperture through which the air is admitted to the bottom of the fireplace, or by an adjustable opening above the fireplace, which will diminish the effective draught as its size is increased, or by a combina tion of both of these contrivances. Often an arti ficial cr forced draught is given to a chimney by means of a fan or blower, a steam-jet, or the exhaust of a steam-engine which is so arranged that it forces a current of air upward through the tine.
There is reason to believe that the chimney, in its present sense of a funnel from the hearth or fireplace to the roof of the house, is a modern invention. In Greek houses it is supposed that there were no chimneys, and that the smoke es caped through a hole in the roof. What the ar rangement was in houses in which there was an tipper story is not known: perhaps the smoke was conveyed by a short funnel through the side •all of the house, which seems to have been the first form of chimney invented in the Middle Ages.
The Roman ca min II s. again, was not a chimney, but a sort of stove; and it has been a suijeet of much dispute whether the Romans had any arti ficial mode of Carrying off the smoke, or whether it was allowed to eseape throvigh the doors. iv ill (IOM'S. and openings in the roof. As the climate and the habits of the people both led to the houses of the ancients heing very such 1110re open than ours are. it is probable that the occa sional fires which they had of wood or charcoal may have given them no great inconvenience. It is known. besides, that the rooms in Roman houses were frequently heated by means of hot air, which was brought in pipes from a furnace below. In F.nglanit there is no evidence of th • use of chimney-shafts earlier than the Twelfth Century. In Rochester Castle (c. IR10). com plete fireplaces appear: hut the flues go only a. few feet up in the thickness of the wall, and are then turned out through the will in the back of the fireplace, the openings being small oblong holes. The earliest ehimney-shafts are circular. and of considerable height. Afterwards chim secs are found in great variety of forms. Pre vious to the Sixteenth Century many of them are short, and terminated by a spire or pinnacle, having apertures of various shapes.
These apertures are sometimes in the pinnacle, sometimes under it. the smoke escaping as from some modern manufacturing chimney-stacks, which are built in the form of an Egyptian obe lisk. Clustered chhnney-stacks do not appear until late in the Fifteenth Century. when they weal to have been introduced simultaneously with the use of brick for this purpose. Each of the earlier clustered chimneys consists of two flues which adhere to each other, and are not set separate, as afterwards was the practice. Long after they were invented. and in use for other rooms, our ancestors did not generally introduce them into their halls, which, till the end of the Fifteenth or beginning of the Sixteenth Century, continued as formerly to be heated by a tire on an open hearth in the centre of the hall, the smoke escaping through an opening in the roof known by the name of bourn. In many of the older halls in which chimneys exist they have evidently been inserted about this period.