at night air,
especially in cities, is distinctly purer than day air, on account of
the fact that there is much less traffic at night to stir up dust.

[Sidenote: Protection From Cold]

It is very important, in any sleeping balcony, to be protected from the
wind by a sash on one or two or--in very windy places--three sides. But
of course sleeping out-of-doors does not reach its maximum efficiency if
there is too much protection, that is, if the sleeping-out place is so
shut in that very free currents of air are not secured. An outdoor
porch really ceases to be an outdoor porch, when enclosed on four sides.

A roll curtain (preferably rolling from the bottom) can be arranged on
the open side or sides, to be used in case of storms only. In cold
weather a thick mattress, or two mattresses, should be used. It is not
only what is over the sleeper, but also what is under him, that keeps
him warm. The body should be warmly clad, and the head and neck
protected by a warm cap or helmet or hood. To prevent the entrance of
cold air under the bedclothes, one or more blankets should be extended
at least two feet beyond the head, with a central slit for the head.
Early awakening by the light may, if necessary, be prevented by touching
the eyelids with burnt cork, or by bandaging the eyes with a black cloth
or stocking. Sheets should be well warmed in the winter-time before
being used. They can easily be warmed with a hot-water bag, flat-iron,
or soapstone. Blankets next to the skin are not hygienic.

[Sidenote: Sleeping-tents]

Sleeping out is really much easier than most people imagine. In fact,
few, if any, of the other cardinal rules of hygiene are so easy to
obey. Where a sleeping-porch is not available, an inward window tent can
always be had which puts the sleeper practically out-of-doors and at the
same time cuts off his tent from the rest of the room.

[Sidenote: Outdoor Tents]

An outdoor tent must be kept well opened. Otherwise it fails of its
purpose. The common opinion that a tent is ventilated through the
"meshes" of the canvas is erroneous. Canvas is a tightly woven fabric
and impervious to air. That is why it makes good sails. One of the most
modern boys' camps has given up the use of tents altogether, employing
instead open wooden "shacks," because of the difficulty of keeping the
tents sufficiently open, especially in rainy weather.

Complete directions for convenient out-of-door sleeping will be
furnished,