pared his glafs by beating it to powder, and wafhing it very clean;
he then took a little o f this glafs upon the {harp point o f a filvef
needle, wetted with fpittle, and held it in the flame, turning it
about till a glafs ball was formed; then taking it from the flame,
he afterwards cleaned it with foft leather, and' fet it in a brafs
cell.
1
No perfon has carried the ufe o f thefe’ globules fo far as T . Di
Torre, o f Naples, nor been fo dexterous in the execution o f ■
them ; and if others have not been able to follow him in the fame'
line, it may be fairly attributed to a want of that delicacy o f
touch for adj tiffing the objefts- to their focus,- and that ae'U'teflefs.
of vifion which can only be acquired by Idiirg jmafffieel P. Tcifrfe
has alfo deferibed, more minutely than any othef autherj' the
mode of executing thefe globules, which, as it throws much light
upon the preceding defcription by Dr. Hooke, will not, it is prefumed,
be unacceptable' to the reader.
Three things are neCeffary for forming o f thefe globules:
1. A lamp and bellows, fitch as are uféd by the glafs-blowérs *
2. A piece o f perfeft tripoli f 3- A variety o f fmall glafs rod’s:.
When the flame o f the lamp is blown in an'; hbrizohtal! dim£fiony
it will be found t o eonfift of two parts f frorir the bafei; fo- about
two-thirds of it’s length, it is o f a white colour; beyond this, it
is tranfparent, and colourlels. It' is this trafllparent part which
is to be fifed for melting the glafs, bécaufe by this it will not bë
in the leaft fullied; but it will be immediately foiled, i f it touches':
the white part of the flame. The part of the glafs which is pre-
fented to the flame, ought to be exceeding clean, and great care
fliould be taken that it be not touched by thé fingers. I f the
6 glafs
MIL
glafs r,o,d .has contracted any fpots, it muft either be thrown away,
or,th.e parts that are fp.otted muft pe cut off.
Th? piece ,of trippli wpich is to be tiled in forming the glo-
bplgs, fliould be flat on one fide, and fo large-, that it may be
handled conveniently, and proteft the fingers from the flame. A
piece four on five inches long, and three or four inches thick, will
.anfwer very well. The heft tripoli for this purpofe, is o f a white
■ colour, with afing grain, heavy and compacl, and which, after
it has been calcined, is of a red colour. This kind refills the fire
belt, is not apt to break when calcined, and the melted glafs does
not adhere to it. T o calcine this tripoli, cover it well all round
with charcoal nearly red hot, leaving ft thus till the charcoal is
quite cold; it may then be taken out. Let feveral hemifpherical
cavities be made on the flat-fide o f the tn p oli; they fliould be
o f different fizes, nicely poliflied, and neatly rounded at the
edges, in order to facilitate the entrance o f the flame. The large
globules are to be placed in the large cayities, and the minuter
ones in the fmall cavities. The holes in the tripoli njuft never be
touched with the finger. I f it is neceffary to clean them, it fliould
be done with white paper; the larger globules may be cleaned
with wafh leather. The glafs rods fliould be o f various fizes, as
o f i-loth, i -20th, 1-30* of an inch in diameter, as clean and
free from fpecks and bubbles as poflible.
T o MAKE SMALL GLASS MICROSCOPIC GLOBULES.
Take two rods o f glafs, one in each hand, place their exr
tremities clofe to each other, and in th,e pureft part o f the flame;
when you perceive the ends to be fufed, feparate them from each
B a other;