t the
trigger catch; if this be omitted the gut gets worn through very
quickly. In order to decide how far it is permissible to bend the
bow, the quickest way is to make a rough experiment on a bit of the
same plank from which the bow is to be cut, and then to allow a small
factor of safety. In the figure the bow is of lance-wood and is more
bent than would be suitable for pine.

The bow itself is tapered from the middle outwards just like any other
bow. If thick threads are required, the above considerations are
modified by the fact that quartz opposes a considerable resistance to
drawing, and that consequently the arrow must not only have a high
velocity, but a fair supply of energy as well; in other words, it
must be heavy. A thin pine arrow instead of a straw generally does
very well, but in this case the advantage of using pine for the bow
vanishes; and in fact lance-wood does better, owing to the greater
displacement which it will stand without breaking. This of course
only means that a greater store of energy can be accumulated at one
bending.

I had occasion to investigate whether the unavoidable spin of an arrow
about its axis produces any effect on the thread, and for this purpose
made arrows with inertia bars thrust through the head, i.e. an arrow
with a bit of wire run through it, perpendicular to its
length--forming a cross in fact--the arms of the cross being weighted
at the extreme ends by shot. This form of arrow has a considerable
moment of inertia about its longer axis, and consequently rotates less
than a mere straw, provided that the couples tending to produce rotation
are not increased by the cross arm, or the velocity too much reduced.
Shooting one of these arrows slowly, I could see that it did not
rotate, and when fired at a high velocity, it generally arrived at the
target (placed at varying distances front bow) with the arms nearly
horizontal, thus showing that it probably did not rotate much.

I did not succeed in this at the first trial, by any means. The
threads got in this way were no better than those made with a single
straw, whence we may conclude very provisionally that the spin of the
arrow has only a small effect, if any, on the quality of the threads.

Feathering the arrow, in my experience, tends, if anything to make it
spin more; for one thing, because it is practically impossible to lay
the feathering on straight.

After the arrow is shot, it remains to gather i