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The Catapult
Fig. 6. - The Skein of Cord.
C. The skein as it appears when tightly twisted up by the winches. Compare
with AA, fig. 3, p.14.
Cord of Italian hemp, about 1/4 in. thick, is excellent for small catapults.
For Large ones, horsehair rope, 1/2 in. thick, is best and most elastic.
Whatever is used, the material of the skein must be thoroughly soaked in
neat's foot oil for some days previously, or it is sure to fray and cut
under the friction of being tightly twisted. Oil will preserve the skein
from damp and decay for many years.
How to Work the Catapult
There is little to write under this heading; as the plans, details of
construction and illustrations will, I trust, elucidate its management.
The skein should never remain in a tightly twisted condition, but should
be untwisted when the engine is not in use.
Previous to using the catapult its winches should be turned with the
long spanner, fig. 1, p. 10, first the winch on one side of the engine
and then the one on the other side of it, and each to exactly the same
amount.
Small numerals painted on the sides of the large wheels, near their
edges, will show how much they have been revolved; in this way their rotation
can be easily arranged to correspond.
As the skein of the cord is being twisted by the very powerful winches,
the arm will gradually press with increasing force against the cross-beam
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