ars a ton. Enough coal will have
to be burned in addition to compensate for radiation, or, in other
words, it requires a certain amount of coal to keep an empty room warm
in winter without any question of ventilation, and in some badly built
houses this amount is large.

_Relation of heating to ventilation._

It does not follow because much heat is lost in this way that the
ventilation is good, since the heated air may ascend to the ceiling and
there escape without influencing the ventilation. In fact, one of the
first principles of ventilation is that as soon as regular inlets and
outlets are provided, all other openings ought to be rigidly closed.
Then and then only can the warmed pure air be admitted as desired, at
the points intended, and the full value of the heat utilized. Especially
is this control of openings important in ventilating barns. Here each
animal is a natural heater, warming the air by direct contact and by
rapidly breathing in and out large volumes of air which are thereby
changed to a temperature of over ninety degrees Fahrenheit. The air
around their bodies being warmed rises to the ceiling and spreads out to
the two sides and is there gradually cooled and at the same time mixed
with fresh air which enters at the top, so that the cow is constantly
supplied with freshened air. A flue is needed to carry the foul air up
through the roof, and fresh-air inlets in the outer walls on both sides
are required, and with these openings carefully controlled and with no
others interfering, the stable may be well ventilated, as shown in Fig.
21 (after King).

[Illustration: FIG. 21.--Cow-barn ventilation.]

In all cases where ventilation is to be practiced, the walls and ceiling
should not merely be tight in themselves, but they should be double, and
the strictest attention paid to limiting the amount of heat lost by
radiation. All the heat used ought to be concerned in ventilation, and
in that only. To secure air-tight walls and ceiling, the studding and
joists should be boarded in, both on the inside and out, and the space
between should be filled with shavings, straw, dry moss, or any similar
fibrous substance. The outside sheathing must be well laid and must be
water-tight in order that rain shall not penetrate to the inside of the
wall, and the roof must be tight so that the ceiling filling does not
get wet and rot.

The choice, therefore, so far as ventilation of either house or barn
goes, lies betwe