n the thread, and if
the latter is at all thin, we have a rather troublesome job. In a
thread thirty or forty feet long, the most uniform part generally lies
in the middle if the thread is thin, i.e. of the order of a
ten-thousandth of an inch in diameter. If the thread is thick the
most uniform part may be anywhere. The part of the thread required is
generally best isolated by passing a slip of paper under it at each
end and cementing the thread to the paper by means of a little
paraffin or soft wax, and then cutting off the outer portions. One
bit of paper may then be lifted off the calico, and the thread will
carry the other bit. In this way the thread may be taken to a
blackened board, where it may be mounted for stock.

By passing the two ends of the thread under a microscope, or rather by
breaking bits off the two ends and examining them together, it is easy
to form an Opinion as to uniformity.

Mr. Boys has employed an optical method of examining threads, but the
writer has invariably found a high-power microscope more convenient
and capable of giving more exact information as to the diameter of the
threads.

The beginner--or indeed the practised hand--need not expect to get a
thread of the exact dimensions required at the first shot. A little
experience is necessary to enable one to judge of the right thickness
of the needle for a thread of given diameter. The threads are so
easily shot, however, that a few trials take up very little time and
generally afford quite sufficient experience to enable a thread of any
required diameter to be prepared.

It is no use attempting to heat an appreciable length of needle; if
this be done the thread almost invariably has a thick part about the
middle of its length.. It is sufficient to fuse at most about
one-twentieth of an inch along the needle before firing off the bow.
This can be done by means of the smaller oxygas blow-pipe jet
described in the article on blow-pipes for glass-blowing, Sec. 14. The
flame must of course be turned down so as to be of a suitable size. A
sufficiently small flame may be got from almost any jet.

If the needle be not equally heated all round, the thread tends to be
curly; indeed by means of the catapult, threads may be pulled which,
when broken, tend to coil up like the balance-springs of watches, if
only care be taken to have one side of the needle much hotter than the
other.

Sec. 85. When examining bits of threads, say