The escape of animal heat from the body forms a subject which is much
more complicated, and much more important, than the one we have met to
consider, but it is impossible within the limits of our time to refer to
it, except in the measure that is strictly necessary to elucidate the
principles that should control the construction of the punka.
It has often been said that every engineer on his arrival in India sets
about improving this useful apparatus; but if we may judge from the
endless variety of forms which may be seen in shops and offices, in
public and in private buildings, no general principle of construction has
been recognized, and the punka, as we see it, seems to depend, for its
form, more upon the taste of the workman who makes it than on anything
else.
We shall begin by directing our attention to the suspended punka, which
is usually hung from the ceiling, and put in movement by a cord. The
object of this class of punka is to produce a downward current of air by
swinging to and fro, and the best punka is the one which throws downward
the greatest quantity of air with the smallest applied force.
The swinging punka is one of the simplest forms of mechanism; it can be
fitted up with the most primitive materials, and however badly made, it
will always have _some_ effect. This fact has its good and its bad
aspects; it brings a certain comfort within the reach of all, but it
removes a great part of that _necessity_ which, as we all know, is the
mother of invention.
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