is the cutting edge.

3. _A larger Diamond that has been "re__set_." That is to say,
_re-ground_: the diagonal marks like a St. Andrew's Cross show the
grinding down of the old facets by which the new cutting edge has been
produced. Magnified 10-1/2 diameters.

4. No. 2 _seen from the side_. Magnified 10-1/2 diameters; the cutting
edge faces towards the left.

[Illustration: IX.--Micro-photographs from details connected with Glass
Work.]

PLATE X.--_Micro-photographs of Glass-cutting_ Very difficult to
explain. "A" is a sheet of glass seen _in section_ multiplied 15-1/2
diameters. The black marks along the _top edge_ are diamond-cuts, good
and bad, coming _straight towards the spectator_. The two outside ones
are very _bad_ cuts, far too violent, and have split off the surface of
the glass. Of the two inner ones the left-hand one is an ideally good
cut, no disturbance of the surface having occurred; the right-hand a
fairly good one, but a little unnecessarily hard. Passing over B for the
present--C is a similar piece of glass also magnified 15-1/2 diameters,
with _wheel-cuts_ seen endwise (coming towards the spectator). The one
on the left is a very bad cut, the surface of the glass having actually
split off in flakes, the next to it is a perfect cut where the surface
is intact, and note that though not a quarter so much pressure has been
employed, the split downward into the glass is deeper and sharper than
in the violent cut to the left, as is also the case with the two other
moderately good cuts to the right.

D, E--_Wheel-cuts._ In these we are looking down upon the surface of the
glass. They are bad cuts, multiplied 20 diameters; the direction of the
cut is from left to right. In the upper figure the flake of glass is
split completely off but is still lying in its place. In the lower one
the left-hand half is split, and the right-hand only partially so,
remaining so closely attached to the body of the glass as to show (and
in an especially beautiful and perfect manner) the rainbow-tinted
"Newton's rings" which accompany the phenomenon of "Interference," for
an explanation of which I must refer the reader to an encyclopaedia or
some work on optics. _Good_ cuts seen from above are simply lines like a
hair upon the glass, but the diamond-cut is a coarser hair than the
wheel-cut.

If you now hold the illustration _upside down_, what then becomes the
top edge of section C shows a wheel-cut seen sideways along th