CHI above mentioned. When chimnies are constructed in a pyramidal or tapering form, especially if the house be of a considerable height, there is much reason to apprehend that they will smoke : the air of a room being rarefied, is forced into the funnel of the chimney, and re- ceives from the fire an additional impetus to carry up the smoke. Thus it is evident that, as the smoke ascends, the impelling force is les- sened ; it moves slower, and con- sequently requires a greater pro- portion of space to circulate through : whereas, in the usual way; it has less room, from the sides of the- chimney being gradually contracted. Aldiough this method of con- structing chimnies may not meet with general approbation, because it is supposed that the wider a chimney is at die top, the more liberty the wind has to blow down 5 yet, on the other hand, it is obvi- ous that, from the structure of the chimney, and from other causes, the wind, having no resistance to overcome, must necessarily return, and thus facilitate the free egress of the smoke. In the usual man- ner of building pyramidal chimnies, when a current of air rushes down- wards, the wind and smoke are ih a manner confined, and as the resistance is less from below, the smoke bursts out into the room. Hence the reverse method before suggested, has proved effectual, after every other expedient had failed, and even in a house, stand- ing in the most disadvantageous situation, namely, under a lofty mountain to the southward, from which blasts were blown down upon it. A vent was carried up without angles, as perpendicular as possible, being made several inches wider at the top than at the bottom : the CHI [517 funnel was contracted in a throat directly above the fire-place, and widened gradually upwards. Since that time, the house has not only ceased to smoke, but, when the doors stand open, the draught is so strong that it will carry a piece of paper up to the top of the chim- ney. The advantage of erecting chimnies after this mode, are so evident, that we venture strongly to recommend its adoption ; for, independendy of their being ex- empt from smoking, and contribut- ing to purify the atmosphere, by the rapid current of air continually circulating through the apartment, it will prevent large quantities of soot from accumulating, and con- sequently remove every apprehen- sion of their taking fire. Various other experiments have been made, with a view to prevent or cure smoky chimnies : of these we shall enumerate only the two following, which deserve pardcular notice. The first is, not to suffer the height of die mantle to exceed one- third of diat of the room, and to carry the jaumbs and breast up- right, at least to the ceiling, when they should be turned or sloped as easily and gradually as possible. The jaumbs from die hearth to the mantle should describe the form of a curve ; and the lower part of the mantle, a broad horizontal plane : the distance from the inside of the breast to the back, on each side of the diroat, being from ten to four- teen or sixteen inches, according to the size of the chimney. This mode of reducing smoky chimnies, we are informed, has repeatedly been found successful. Another method, which is at- tended with but little expence, consists in setting the grate, if a Bath stove, eleven or twelve inches L 1 3 distant
