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 encyclopædia 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 the section of the glass which it has divided, the direction of this cut being from left to right.
In the same way section "A" seen upside down gives the appearance of a diamond-cut, also from left to right, and multiplied 15-1/2 diameters, while "B" held in the same position gives the same cut multiplied 78 diameters. The nature of these things is discussed at p. 48.
In their natural colour, and under strong light, they are very beautiful objects under the microscope. Even a 10-diameter "Steinheil lens," or still better its English equivalent, a Nelson lens, will show them fairly, and some such instrument, opening out a new world of beauty beyond the power of ordinary vision, ought, one would think, to be one of the possessions of every artist and lover of Nature.
The illustrations that follow are from the work of the author and his pupils conjointly. Those in which no design has been added are for clearness' sake described as "by the author"; but it is to be understood that in all instances the transcribing of the work in the glass has been the work of pupils under his supervision. All design of diaper, canopy, lettering,
and quarries is so, in all the examples selected.
X.—Micro-photographs. Diamond and Wheel Cuts seen in Section and Plan.
PLATE XI.—From Gloucester Cathedral—"St. Boniface" by the author and his pupils.