d. But it has invariably
proved that with a concave surface the kite receives too much of the
breeze and becomes quite uncontrollable. The amount of spring that
must be given the cross-piece is in proportion to its length, Mr.
Eddy's rule being to spring the cross-stick, by means of a cord
joining the two ends like a bow, until the perpendicular between the
point of juncture of the two sticks and the centre of the cord is
equal to one-tenth of the length of the cross-stick, or a little more
than one-tenth, if the kite is to be flown in very high winds.

It is of the first importance to keep the two halves of the kite on
the right and the left of the upright stick perfectly symmetrical. And
this is by no means an easy matter. It often happens in bending the
cross-stick that, owing to differences in the fibre and elasticity of
the wood, one side bends more than the other, with the result that
the two halves present different curves and consequently unequal wind
areas. To offset this difficulty, and also to strengthen the skeleton,
Mr. Eddy's practice is to add a bracing piece at the back of the
cross-stick--a piece about one-fourth of the length of the cross-stick
itself, and of the same width and thickness. If the two halves of the
kite are already quite symmetrical, he places this bracing stick with
its centre directly even with the point of juncture of the two large
sticks, its two ends being fastened with twine to the cross-stick,
about nine inches on either side of the crossing-point. But if one
half of the cross-stick shows a greater bend than the other, he places
the longer arm of the bracing piece toward the side that bends the
most, thus presenting a greater leverage against the wind on that side
than on the other, and so equalizing things.

With the two sticks and the brace all thus properly in place, a
supporting frame for the paper or cloth is formed by running, not
cord, but fine picture wire, over the tips of the sticks, notched to
hold it in place, in the ordinary way. Then, with a thin, clear paste
made of starch, the paper may be laid on, care being taken to paste
the edges so as to leave a certain amount of slack or looseness in
the part of the kite below the cross-stick, so that each of the lower
faces will present concave wind surfaces. To preserve the required
equilibrium, it is important that the amount of looseness in the paper
be equal on the two sides; and in order to keep it so, it is necessary