THE TOUNG SCIENTIST. 
33 
" shanks " or nibblers, which are a species 
of pliers, made, in preference, of soft iron, 
as this grips the glass without slipping, as 
hard steel would do. This instrument, of 
a larger size, is capable of removing slivers 
of glass from the edges of a plate upwards 
of one inch in thickness. 
"All glass is much softer than hardened 
steel ; but if this is set to cut in a dry state, 
the heat generated at the working or 
abrading point softens the cutting edge, 
and speedily destroys its action; but if 
some turpentine is applied, this quite pre- 
vents the softening of the tool. In the 
lathe, or with a common Archimedean 
drill, holes may be drilled through thick 
plate-glass with surprising rapidity, if 
kept well bathed in turpentine. Masses 
of glass may also be turned in the lathe 
with a steel tool, if plentifully supplied 
with turps, and run at a moderate speed. 
" The first experimental parabolic con- 
densers were made from plate-glass Ih 
inches thick ; pieces of this nibbled rudely 
to form, were cemented on to a chuck. 
The T-rest was next placed nearly on a 
level with the top of the work, and an old 
triangular saw-file, kept sharp on one side 
only by repeated applications to the grind- 
stone, was then held on the rest, so as 
to attack the revolving glass slantways, 
or spoke-shave fashion, with plenty of 
turpentine. By these means the glass was 
quickly reduced to form, so as to fit the 
template ; and the ridges left by the file 
were swept away by means of small leaden 
laps, fed with emery and water of increas- 
ing fineness. The polish was obtained by 
a rubber of willow- wood, cut crossways of 
the grain, used with crocus (peroxide of 
iron) and water, and at last a lump of 
beeswax with very fine crocus was em- 
ployed for the final polish. 
" For working small concave lenses, as 
nearly as possible to their final form, a 
great deal of accurate and skilful turning 
is required. For this delicate work steel 
tools are quite unsuited, and diamond 
points are invariably used. The common 
practice of mounting these has been to 
solder them with brass and borax, by 
means of the blow-pipe, into the end of a 
steel tube about the size of a watch-key, 
leaving a hole behind to prevent the dia- 
mond from being blown out during the 
fusion; but I have never found this 
method secure for small splinters. The 
brass has really no affinity for the dia- 
mond, but rather tends to avoid it ; and 
this is frequently only held in by the glaze 
or flux. The loss of several diamonds in- 
duced me to abandon this practice, and 
since adopting the following mode I have 
never lost one. 
" I take a piece of copper wire, about 
l-12th of an inch thick, and drill a shallow 
hole in the end, of the size and depth re- 
quired to contain the diamond. Fig. 4. A 
Fig. 4. Fig. 5. Fig. 6. 
piece of steel, turned out with a bell- 
mouth, and hardened, is shown in Fig. 5. 
This is spun rapidly in the lathe, a drop 
of oil is applied, and the end of the copper 
rod containing the diamond is pressed 
hard in, at the same time giving it a 
slight rolling motion. Speedily the cop- 
per is compressed tightly round the dia- 
mond, as in Fig. 6, which becomes very 
firmly imbedded in the soft metal ; and if 
the operation is carried too far, the cop- 
per rises over the point and completely 
buries the splinter. 
"By mutual abrasion, the diamonds 
rapidly grind each other away, and two, 
mounted in wires in this way, may be kept 
mutually to a sharp point by chucking 
one in the lathe and using another as a 
turning-tool. In employing these dia- 
monds for turning glass, no particular 
directions are needed ; they seem to cut 
rather better if the w^ork is kept slightly 
moist. 
" The most convenient way, for the ama- 
teur, of reducing the substance, or giving 
the rough rounded form to small lenses, 
is a large plate of zinc and coarse emery 
and water ; iron is too hard, lead too soft, 
and copper poisonous." 
