he ordinary way, and this is often a
difficulty.

I ought to say that I have never succeeded in boring the barrel of a
glass tap by either of these methods. [Footnote: I have been lately
informed that it is usual to employ a splinter of diamond set in a
steel wire holder both for tap boring and for drilling earthenware for
riveting. The diamond must, of course, be set so as to give
sufficient clearance for the wire holder.

For methods of using and setting diamond tools see Sec. 55. It will
suffice to say here that a steel wire is softened and filed at one end
so as to form a fork; into this the diamond is set by squeezing with
pliers. The diamond is arranged so as to present a point in the axis
of the wire, and must not project on one side of the wire more than on
the other. It is not always easy to get a fragment satisfying these
conditions, and at the same time suitable for mounting. A drop of
solder occasionally assists the process of setting the diamond.

In drilling, the diamond must be held against the work by a constant
force, applied either by means of weight or a spring. I made many
trials by this method, using a watchmaker's lathe and pressing up the
work by a weight and string, which passed over a pulley. I used about
40 ounces, and drilled a hole 3/32 in diameter in flint glass at a
speed of 900 revolutions per minute to a depth of one-eighth of an
inch in eight minutes. I used soap and water as a lubricant, and the
work was satisfactory.

Since this was set up, I have been informed by Mr. Hicks of Hatton
Garden that it is necessary to anneal glass rod by heating it up to
the softening point and allowing it to cool very slowly under red-hot
sand or asbestos before boring. If this be done, no trouble will be
experienced. The annealing must be perfect.]

Sec. 39. For boring large holes through thick glass sheets, or, indeed,
through anything where it is necessary to make sure that
no accident can happen, or where great precision of position and form
of hole is required, I find a boring tube mounted as shown in the
picture (Fig. 36) is of great service. Brass or iron tube borers do
perfectly well, and the end of the spindle may be provided once for
all with a small tube chuck, or the tubes may be separately mounted as
shown. A fairly high speed is desirable, and may be obtained either
by foot, or, if power is available, is readily got by connecting to
the speed cone of a lathe, which is p