or ordinary purposes I have found a bow of
lance-wood succeed quite as well. The trigger of the bow consists of
a simple pin passing through the stock and fastened at its lower end
to a string connected with a board which can be depressed by foot. In
the figure an ordinary trigger is shown, but the pin does just as
well.

Fig 67.

The arrow is made out of about 6 inches of straw, plugged up aft by a
small plug of pine or willow fastened in with sealing-wax, and
projecting backwards one-eighth of an inch. This projection serves a
double purpose: it gives a point of attachment for the quartz needle,
and on firing the bow it forms a resisting anvil on which the string
of the bow impinges. The head of the arrow is formed by a large
needle stuck in with sealing-wax, and heavy enough to bring the centre
of gravity of the arrow forward of one-third of its length, the
condition of stability in flight.

Fig. 68.

It is not necessary to employ any feathering for these arrows; though
I have occasionally used feathers or mica to "wing the shaft" no
advantage has resulted therefrom.

To get fine threads a high velocity is essential. This is obtained by
considering (and acting upon) the principles involved. The bow may be
regarded as a doubly-tapering rod clamped at the middle. After
deflection it returns towards its equilibrium position at a rate
depending in general terms on the elastic forces brought into play,
directly, and on the effective moment of inertia of the rod, inversely
(see Rayleigh, Sound, vol. ii. chap. viii.) If the mass of the
arrow is negligible compared with the bow, the rate at which the arrow
moves is practically determined by that attained by the end of the
bow, which is a maximum in crossing its equilibrium position.

The extent to which the arrow profits by this velocity depends on the
way the bow is strung. It will be greatest when the string is
perpendicular to the bow when passing its equilibrium position; or in
other words, when the string is infinitely long. Since the string has
mass, however, it is not permissible to make it too long, or its
weight begins to make itself felt, and a point is soon reached at
which the geometrical gain in string velocity is compensated for by
the total loss of velocity due to the inertia of the string. In
practice it is sufficient to use a string 10 per cent longer than the
bow.

It is well to use a light fiddle string, served with waxed silk a