et is cut into the wall and a flue carried up
through the roof, the flue should be preferably near the floor and on
the side of the room opposite the window or inlet. With such an
arrangement (see Fig. 20) the air entering rises at first, but sinks at
once because of the temperature, so that the direction of the air
currents are diagonally across the room from the ceiling to the floor,
thus renewing and changing all the air particles except those directly
over the outlet. Where the air is introduced mechanically, that is,
forced into the room, it is better to have the inlet and outlet on the
same side, so that the entering air is shot in at the top, flowing
across the room, then sinking and coming back, just below the point
where it entered.

[Illustration: FIG. 20.--Outlets into the walls.]

_Ventilation of stables._

All that has been said on the subject of ventilation in houses applies
equally well to the ventilation of stables, and a little book by
Professor King of the University of Wisconsin, entitled "Ventilation,"
deals most thoroughly with the principles and practices of ventilation,
not merely for dwellings but also for stables. Professor King proves by
his experiments that the condition of cattle is much improved and that
the milk-giving qualities are increased by a proper supply of fresh air,
and in the book referred to, he gives a number of examples of the proper
construction to provide adequate ventilation. It is most convincing to
see how unscientific is the old-fashioned underground stable, the sole
idea of which was to conserve the animal heat by crowding together the
cows and by absolutely excluding the outside air. For further details of
his work, its principles and practices, the reader is referred to the
book, which may be obtained from the author at Madison, Wisconsin.

_Cost of ventilation._

To ventilate a house is expensive, and to ventilate a barn requires not
only a certain expenditure of money but also a considerable amount of
judgment. It is evidently cheaper to heat the same air in a room over
and over than to be continually admitting cold fresh air, which will
have to be warmed. This extra cost is, however, not excessive, when the
movement of the air currents is properly controlled. The cost of warming
the air necessary for ventilation for five persons should not be, at the
rate of 1000 cubic feet of air to each person, more than ten cents a day
in zero weather, with coal at five doll