e 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.

There are some very important natural laws which are illustrated in the
punka. The first is that which governs the movement of the pendulum. The
number of swings it makes per minute depends on the length of the
suspending cords; a pendulum three feet long will swing 621/2 times per
minute, and a pendulum six feet long will swing 441/4 times per minute.
Whether the swings are long ones or short ones, the number per minute is
still the same. You cannot, therefore, alter the natural rate of movement
of a punka unless you pull it at both sides.

The next law is that which determines that the angles of incidence and of
reflection are equal. This in simple language means that it is useless to
expect a good downward current of air from a slow moving and heavy punka,
with long suspending cords which keep it nearly always in a vertical
position to its plane of movement. Striking the air squarely as it does
in its forward and backward movement, it throws almost as much air upward
as downward, and of course all the air that is propelled in any other
than a downward direction represents just so much power wasted.

One mo