resumably permanently belted to
the motor.

Fig. 36.

After trying tubes armed with diamond dust, as will be presently
explained, I find that emery and thin oil or turpentine, if liberally
supplied below the glass, will do very nearly as well. The tube
should be allowed to rise from the work every few seconds, so as to
allow of fresh emery and oil being carried into the circular grooves.
This is done by lifting the hinged upper bearing, the drill being
lifted by a spiral spring between the pulley and the lower bearing
shown at B. The glass may be conveniently supported on a few sheets
of paper if flat, or held firm in position by wooden clamps if of any
other shape. In any case it should be firmly held down and should be
well supported. Any desired pressure upon the drill is obtained by
weighting the hinged board A.

Sec. 40. The following method was shown to me by Mr. Wimshurst, but I
have not had occasion to employ it myself. It is suitable for boring
large holes through such glass as the plates of Mr. Wimshurst's
Influence machines are usually made of. A diamond is mounted as the
"pencil" of a compass, and with this a circle is drawn on the glass in
the desired position. The other leg of the compass of course rests on
a suitable washer.

To the best of my recollection the further procedure was as follows.
A piece of steel rod about one-eighth inch in diameter was ground off
flat and mounted in a vice vertically, so as to cause its plane end to
form a small horizontal anvil. The centre (approximately) of the
diamond-cut circle of the glass was laid on this anvil so as to rest
evenly upon it, and the upper surface (i.e. that containing the cut)
was then struck smartly with a hammer, completely pulverising the
glass above the anvil. The hole was gradually extended in a similar
manner right up to the diamond cut, from which, of course, the glass
broke away.

A similar method has long been known to glaziers, differing from the
preceding in that a series of diamond cuts are run across the circle
parallel to two mutually perpendicular diameters. A smart tap on the
back of the scored disc will generally cause the fragments to tumble
out. I have never tried this myself, but I have seen it done.

Large discs may easily be cut from sheet glass by drawing a circular
diamond cut, and gradually breaking away the outer parts by the aid of
additional cuts and a pair of pliers or "shanks" (see Fig. 44).

Sec.