where one would not expect it; for it is not uncommon in
ill-contrived buildings, instead of having a separate funnel for each
fire-place, to bend and turn the funnel of an upper room so as to make
it enter the side of another flue that comes from below. By this means
the funnel of the upper room is made short, of course, since its length
can only be reckoned from the place where it enters the lower funnel,
and that flue is also shortened by all the distance between the entrance
of the second funnel and the top of the stack; for all that part being
readily supplied with air through the second flue, adds no strength to
the draft, especially as that air is cold when there is no fire in the
second chimney. The only easy remedy here, is to keep the opening shut
of that flue in which there is no fire. Another very common cause of the
smoking of chimnies is, their overpowering one another. For instance, if
there be two chimnies in one large room, and you make fires in both of
them, you will find that the greater and stronger fire shall overpower
the weaker, and draw air down its funnel to supply its own demand, which
air descending in the weaker funnel will drive down its smoke, and force
it into the room. If, instead of being in one room, the two chimnies are
in two different rooms communicating by a door, the case is the same
whenever that door is open. The remedy is, to take care that every room
have the means of supplying itself from without, with the air its
chimney may require, so that no one of them may be obliged to borrow
from another, nor under the necessity of lending. Another cause of
smoking is, when the tops of chimnies are commanded by higher buildings,
or by a hill, so that the wind blowing over such eminences falls like
water over a dam, sometimes almost perpendicularly on the tops of the
chimnies that lie in its way, and beats down the smoke contained in
them. The remedy commonly applied in this case is, a turn-cap, made of
tin or plate-iron, covering the chimney above, and on three sides, open
on one side, turning on a spindle, and which being guided or governed by
a vane, always presents its back to the wind. This method will generally
be found effectual, but if not, raising the flues, where practicable, so
as their tops may be on a level with or higher than the commanding
eminence, is more to be depended on. There is another case of command,
the reverse of that last mentioned; it is where the commanding emin