is
fixed near a pulley. A small piece of lead forms the counterpoise of the
fan, which is thus completely balanced. Over the pulley runs a cord, each
end of which is attached to a pedal. It will be seen that the alternate
motion of these pedals must cause a rotation of the pulley in one
direction or the other, and that consequently the fan will rise or fall
more or less rapidly, and give a quantity of air that varies according to
the rapidity with which the toes are moved.--_La Nature_.

* * * * *

PUNKAS.

[Footnote: Extract from a lecture recently delivered at Bombay.]

By J. WALLACE, C.E.

The function of a punka is to cause a current of air to pass the human
body so that the animal heat may escape more rapidly. This has nothing to
do with ventilation; for if the punka were used in a closed room, it
would still produce a cooling effect on the skin.

Let us for a moment examine into what takes place in this operation, for
a clear idea of the cause of our sensations of heat is absolutely
necessary to enable us to go directly to the simplest and best form of
remedy. The heat we feel, and which sometimes renders us uncomfortable,
is produced _within us_ by the slow combustion of the food we eat.

This heat continues to escape from the whole surface of the body during
the whole lifetime, and if anything occurs to arrest it to any great
extent, the result is fatal.

In cold weather, and especially when there is much wind, the animal heat
escapes very rapidly from the body, and extra clothing is used, not for
any heat it imparts, but simply because it interrupts the escape of the
heat, and thus maintains the temperature of the skin--that part of us
which is most sensible of change of temperature. It is a wonderful fact
that the heat of the interior of the body varies very little in a healthy
man between India and Greenland.

The skin may bear a good many degrees of change of temperature with
impunity, but the blood will only suffer a very small variation from the
normal temperature of 98-4/10 deg. Fahrenheit without serious consequences.

Well, to keep the skin at an agreeable temperature in India we generally
wear a minimum of clothing, and when there is no breeze, we try to
produce one with the punka.

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 impossibl