Chininies. A chimney is an onenine through awall upwards, beginning at one side of a room, and ending at the top of wall : its use is to warm the room, and give passage to the smoke. That part of the opening which faces the room is the place where the fire is put, and conse quently is called the fire place : the tube or hollow proceeding from the fire-place upwards, for givingvent to smoke, is call ed the funnel, or flue: the stone or mar ble laid level with the floor immediately before the fire-place is called the hearth or slab ; and the one under the fire-place the back or inside hearth. The project ing parts of the walls on each side of the fire-place, forming also parts of the sur face of the room, and standing at the ex tremities of the hearth, are called jambs : the head of the fire-place in the surface of a room, resting upon the jambs, is called the mantle : the mantle, and that part of the chimney resting upon it, forming a part of the side of the room, and also the whole side of the flue to the top, is called the breast; the side of the flue opposite to the breast is called the hack ; and the sides of the fire-place contained between the jambsand the hack are called covings. When there are two or more chimnies in the same wall,th e flues of which approach very near to each other, the thin division which separates one flue from another is either called a partition, or a with ; that part of the opening or horizontal section opposite to the mantle of a fire-place is called the throat ; and that turret above the roof of a house, containing one or more flues, is called the shaft.
In stone walls, the most common dimen sions of the sections of flues are from 12 to 13 inches square, for fire-places about 33 feet wide in front; and those in brick walls 14 inches by 9 inches. The area of the section of the flue should always be proportioned to the area of the fire usual ly put in the fire-place, that is, nearly equal to the area of the horizontal section of the fire itself, excepting at the throat The throat should be immediately over the fire, and its horizontal dimensions in the thickness of the wall should not exceed 43, or 5 inches at most The fuel grate, or stove, should be brought as near to the throat as conveniency may require. The cooing should be placed bevelling nearer together at the back than at the jambs, making an exterior angle with the front of the jambs, and an interior angle with the back, of 135 degrees each. The back and covingsforming the sides of the fire-place should be of white materials, such as white stone, or brick covered with plaster, which are most convenient ly put up after the house is built. Most metals are unfavourable for this pur pose. The top of the throat should be quite level, forming an abrupt plane.
Some of the principlesin the construction of chimnies arc very well ascertained, others are not easily discovered till tried. The more the ;sir that goes into the flue is rarefied, with the more force it will ascend, and the higher the flue the great er also will this force be ; therefore the fire should have as little vacancy on either side as possible, and the flue, when con venient, should be carried as high as pos sible, and not have too wide an aperture at the top 1 he situation of doors in a room, the grate being placed too low, and other things, often occasion smoke ; but whatever be the cause of it, if once dis covered the evil may easily be remedied. Circular flues are more favourable for venting than those whose sections arc rectangular.
Vaults. A vault is an interior roof over an apartment, rising in a concave direc tion from the walls which support it, either meeting the vertex in a point or line, as when the section of the arch is Gothic ; or one continued arch from the one abutment to the other, as when the section is a semicircle, or a segment less than a semicircle.
The vertical sections of the intradoes of vaults may be formed by an infinite va of curves ; hut the most elegant forms are either circular or elliptic; which forms of sections have been generally adopted by the ancients of remote antiqui ty, by our ancestors throughout the mid dle ages, and by European nations at the present day. We shall therefore confine ourselves to those vaults which have their extradoes of circular and elliptic sections.
A cylindrical vault is a plain vault, the figure of the extradoes of which is a por tion of a cylindric surface, terminating on the top of the walls which support it in a horizontal plane, parallel to the axis of the cylinder. This is also called a cradle vault.
A cylindroidal vault is a plain vault, the figure of the extradoes of which springs from a horizontal plane ; its section per pendicular to those lines is every where a semi-ellipsis, equal and similar through out, and its base is that of either axis ; or it is sometimes a segment of an ellipsis, less than a semi-ellipsis, having an ordi nate parallel to the axis for its base.
A dome may be defined to be a vault rising from a circular, elliptical, or po lygonal plan or base, such that all hori zontal sections of the intradoes are similar figures, has im; their centres in the same vertical line or axis, and such that thc plans of any two sections may have the sides of siniilar inscribed figures parallel to each other, or that the lig-ures of these plans may be concentric. If the dome is a portion of a sphere, that is, if its base be a circle, and its vertical section thmugh the centre of its base the segment of a circle, then it is also called a cupola.