32 
THE YOUNG SCIENTIST. 
Home-Made Telescopes and Micro- 
scopes— III. 
CUTTING AND ROUGHING OUT THE GLASS. 
TTTHEN ordinary plate glass is used for 
» * simple lenses it is generally cut into 
squares by means of a common glazier's 
diamond, and these squares are worked 
into shape either by grinding or by means 
of a pair of soft pliers. The pressure of 
the pliers, applied near the edges of the 
glass, cause it to crumble away in small 
fragments, and the process, which is called 
shanking or nibbling, is continued until the 
pieces are made circular and of a diameter 
a little larger than the finished size of the 
lenses. If we wish to make a plano-con- 
vex lens and it is found, after careful ex- 
amination, that the surface of the plate 
glass is sufficiently smooth and even to 
answer without further grinding or pol- 
ishing, this surface should be protected 
from scratches by having a piece of paper 
pasted over it. After the glass has been 
roughed out to nearly the right size, the 
paper should be soaked off and the plane 
side of the glass cemented to a metal or 
wooden handle. The cement will protect 
the surface. 
If, however, the lenses are to be ground 
out of discs or blocks of glass, such as are 
sold by the dealers in optical glass, then 
a different plan must be pursued. Glass 
of this kind is too costly to be wasted by 
breaking it into irregular fragments; it 
should be sliced into plates of proper 
thickness by means of a lapidary's slit- 
ting machine. This is simply a disc of 
thin sheet iron which is mounted on a 
mandril and turned up true and smooth. 
It is of importance that the edge of the 
slicer should be quite true and free from 
even minute notches. In the usual lapi- 
dary's slitting machine, the slicer runs 
horizontally, but it may just as well run 
vertically and so be used in a common 
lathe. 
To charge the edge of the slicer, or to 
season it, as it is called, requires some 
care. The diamond powder is easily pro- 
cured from dealers in fine tools, and 
should be quite fine. It is mixed with a 
little oil in a small glass cup or pot pro- 
vided with a cover. To apply it to the 
edge of the iron disc, a little is taken up on 
a small spoon made out of a quill, and the 
hollow of the quill, holding the diamond 
powder, is held against the edge of the 
slicer until the latter is coated. The dia- 
mond particles must now be forced into 
the metal, and this is done by holding a flat 
piece of hard stone, such as agate or flint, 
against the edge. Care must be taken not 
to allow the slicer to cut into the flint or 
agate, as this would force particles of 
diamond into the sides of the slicer where 
they are not wanted. As soon, therefore, 
as the slicer begins to cut the stone it must 
be shifted to a new place. As soon as the 
small quantity of diamond resting on the 
edge of the slicer has been forced into it, 
the margin of the slicer is carefully wiped 
on both sides with the forefinger, in order 
to remove any small portions of the dia- 
mond that may have become accidentally 
lodged on the sides, and these particles 
are pushed to the edge of the slicer and 
pressed in with the charging stone. After 
the edge of the slicer has been once fairly 
charged with the diamond powder, a 
single application is generally sufficient 
for restoring the cutting edge, and under 
the hands of the practical lapidary a 
single seasoning will endure several hours 
work. 
We have given these directions because 
professional lapidaries are inaccessible to 
most of our readers. Where the worker 
wishes to get along with cheaper and 
simpler means, the following directions 
by Mr. Wenham will be found valuable : 
"Pieces of glass maybe readily sliced 
with a circular disc of soft iron, running in 
the foot-lathe, and fed with flour emery 
and water ; the edge of the slicer must be 
frequently notched with the sharp angle 
of an old file. The sample of glass or 
mineral is cemented to the end of a staff, 
and held preferably in the slide-rest. If 
the screw of the rest is taken out and the 
slide made slack, the work can be thrust 
up to the slicer with the pressure of the 
fingers, and there is less risk of fracture 
from undue violence. The sliced glass is 
cut into squares, a little exceeding the di- 
ameter of the intended lenses, by means 
of a glazier's diamond, and the corners 
rounded off with a pair of optician's 
