CHIMNEY (Fr. chem.inge, Lat. caminus). There seems reason to believe that the C., in its present sense of a funnel from the hearth or fire-place 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 escaped through a hole in the roof. What the arrangement was in houses in which there was an upper story, is not known; perhaps the smoke was con veyed by a short funnel through the side-wall of the house, which seems to have been the first form of C. invented in the middle ages. The Roman minima, again, was not a C., but a sort of stove; and it has been a subject of much dispute, whether the Romans had any artificial mode of carrying off the smoke, or whether it was allowed to escape through the doors, windows, and openings in the roof. As the climate and the habits of the people both led to the houses of the ancients being very lunch more open than ours are, it Is probable that the occasional 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 England, there is no evidence of the use of chimney-shafts earlier than the 12th century. In Rochester castle (circa 1130), complete fire-places appear; but the flues go only a few feet up in the thickness of the wall, and are then turned out through the wall to the back of the fire-place, the openings being small oblong holes. The earliest chimney-shafts are circular, and of considerable height. Afterwards, chimneys are found in a great variety of forms. Previous to the 16th c., 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-stalks which are built in the form of an Egyptian obelisk. Clustered chimney-stalks do not appear until late in the 15th when they seem 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 15th, or beginning of the 1Gth c., continued as formerly to be heated by a fire on an open hearth in the center of the hall, the smoke escaping through an opening in the roof known by the name of louvre. In many of the older halls in which chimneys exist, they have evidently been inserted about this period.
The action of a C. depends upon the simple principle, that a column of heated air is lighter than a cooler column of equal height; when therefore a flue full of heated air communicates freely by the lower part with the cooler air around it, the greater weight of the latter pushes the warm air upwards, and thus an ascending current is pro duced. Other conditions being equal, the draught of a C. will thus be proportional to its perpendicular height, and the difference between the temperature within and without it. The straighter and more perpendicular the C., the stronger will be the draught, because the friction of the ascending. current will be less, and the cooling effect of a long or tortuous course will be saved. The maximum efficiency of a given C. is attained when all the air that passes up it enters by the bottom of the fire. In this case, its temperature is raised to the uttermost by passing through the whole of the fire, and the lire is at the same time urged to vivid combustion by the blast thus obtained. A power ful furnace may be constructed by connecting a suitable fire-place, capable of being closed all round excepting at the bottom, with a tall C. ; and the amount of draught may be regulated by increasing or diminishing the aperture through which the air is admitted to the bottom of the fire-place, or by an adjustable opening above the fire-place, which will diminish the effective draught as its size is increased, or by a combination of both of these contrivances.