rdboard disk attached. One of the
disks shall present its edge to the line of movement, and the other its
face.

_Exp. 1._--They are now swinging, and being both of the same gravity
length, they should swing together and for an equal length of time. This
they would do in a vacuum, but you have already observed that one of them
is lagging, and will evidently soon come to a standstill. It is the one
_facing_ the air.

If punkas were pulled from both sides, they might be made very much
lighter than they are at present, but for the sake of simplicity a single
pull is preferred. They must, therefore, be made of such a weight that
they will swing nearly as far on the opposite side as they are pulled on
the near side; any greater weight is useless and only serves to wear out
the suspending cords, which, by the way, are nearly always too numerous
and too thick for their purpose.

_Exp. 2._--Here is a panel punka which we shall try to use without the
customary swing bar. It is of calico stretched on a light wooden frame,
and you will be able to judge if it swings equally on each side of the
post which supports it. The irregularity of its movement shows that it is
too light, so we shall add, by way of swing bar, a bar of round iron one
and a quarter inch thick.

_Exp. 3._--It is now swinging regularly, and experiments have already
proved that the swing bar should not be lighter than this one, which
weighs four and a sixth lb. per foot of length. Iron is the best material
for this purpose, as it offers the smallest surface to the resistance of
the air. The length of the suspending cords is usually a matter of
accident in the construction of a punka, but a little attention to the
subject will soon convince us that it is one of the most important
considerations.

The limit of movement of a punka is to be found in the man who pulls it.
Twenty-four pulls a minute of a length of 36 inches give in practice a
speed of 168 linear feet to the punka curtain. This speed is found to
produce a current sufficiently rapid for practical purposes, and
twenty-four pulls or beats per minute correspond to a length of
suspending cord of fifty inches.

* * * * *

HOW TO MAKE A KITE WITHOUT A TAIL.

The following is the method of making a kite without a tail: All the
calculations necessary in order to obtain the different proportions are
based upon the length of the stick, A'A, employed. Such length being