in of foreign bodies. That part
of the chimney opening into the fireplace is called the _throat_.

=Smoky Chimneys.=--A very frequent cause of complaint in a great many
houses is the so-called "smoky chimney"; this is the case when smoke
and coal gas escape from the chimney and enter the living rooms. The
principal causes of this nuisance are:

(1) A too wide or too narrow diameter of the shafts. A shaft which is
too narrow does not let all the smoke escape; one which is too wide
lets the smoke go up only in a part of its diameter, and when the
smoke meets a countercurrent of cold air it is liable to be forced
back into the rooms.

(2) The throat of the chimney may be too wide, and will hold cold air,
preventing the warming of the air in the chimneys and the consequent
up draught.

(3) The cowls may be too low or too tight, preventing the escape of
the smoke.

(4) The brickwork of the chimney may be loose, badly constructed, or
broken into by nails, etc., thus allowing smoke to escape therefrom.

(5) The supply of air may be deficient, as when all doors and windows
are tightly closed.

(6) The chimney may be obstructed by soot or some foreign material.

(7) The wind above the house may be so strong that its pressure will
cause the smoke from the chimney to be forced back.

(8) If two chimneys rise together from the same house, and one is
shorter than the other, the draught of the longer chimney may cause an
inversion of the current of air in the lower chimney.

(9) Wet fuel when used will cause smoke by its incomplete combustion.

(10) A chimney without a fire may suck down the smoke from a
neighboring chimney; or, if two fireplaces in different rooms are
connected with the same chimney, the smoke from one room may be drawn
into the other.

=Methods of Heating.= =Open Fireplaces and Grates.=--Open fireplaces
and fires in grates connected with chimneys, and using coal, wood, or
gas, are very comfortable; nevertheless there are weighty objections
to them. Firstly, but a very small part of the heat of the material
burning is utilized, only about twelve per cent being radiated into
the room, the rest going up the chimney. Secondly, the heat of grates
and fireplaces is only local, being near the fires and warming only
that part of the person exposed to it, leaving the other parts of the
room and person cold. Thirdly, the burning of open fires necessitates
a great supply of air, and causes powerful draughts.