GRINDING. 
pon filling-the bottle with water, and fhaking the mixture ; 
fo that the coarfeft ‘of the emery will fubfide to the bottom 
firlt; andthe fineft remain at the top: when frefhemery is 
laid on the tools, it is beft done by gently thaking the 
_— and poune out a {mall quantity of the turbid mix- 
ext operation is to grind the brafs convex tool 
with the ‘beuifer upon it, which is’ continued for about a 
quarter of an hour, and sete - convex tool is wrought 
— the bruifer in the When thefe have 
be 
nd both 
ven to 
is made of ery a little more than ee its thicknefs, a 
fomewhat lefs in diameter, of a three. pounds weight, 
with a hole in the middle, a take tee than. that in the 
metal: the handle fhould be cemented on with pitch. The 
upper ‘edge of this weight muft be rounded off, that the 
fingers may not be hurt, and a groove, about the fize of the 
little finger, be turned round jualt below it, for the more con- 
—— holding and pics: the metal off the tools. When 
cahpeoris brafs to metal, are all brought.to the 
past figure, and have Z goo ood furface, the next part of the 
procefs 1 is to ‘ee a correct {pherical figure and a_ fine face 
b 
to’ the metal, upom the hones ; thefe, however, fhould e 
covered with water for at leaft an hour before they are ufed, 
— they will be liable to alter their figure ; and they 
never fuffered to urow rigs whilit they are in. ufe, 
for wi Picts reafo on, 
an 
and. a light hand, the i inequa- 
lities of the ftone will be foon worn off, the mud that is 
generated being wafhed away, every quarter of a minute, 
with a great deal of water. As foon as the hones have 
eae the general figure of the oot and all the turn- 
in s are worn out from them, the ig mult be 
carefully wafhed off, and cleared frem the joins with a 
water. he bruifer and metal muft 
n the fame manner. he — being 
ane d ons - the block, the peuiler muft be w. 
. bbed upon the 
hones in. the. cautious esi occafionally rubbing the 
bruifer upon the hones, in order to hen 
in this waz ay the hone Lema has given a and true 
ght froke or tio in thi 
3 
it quite the..di 
wa avg gen th mea 2 
d. altered for the fhort Baad foeig hn 9: nes. 
diretion, ‘take it ‘off the tool.’ ~The ome ben a 
quite i _ it upon a table ata little. pr me fro 
window as near the window, at fome diftance from 
the rhetal, a looking obliquely on its re tes turn it round 
its. axis, and you will fee at every half turn the grain 
given by the laft _— a flath upon your eye at once 
over the whole face etal, This is a certain pions 
of a arn {pherical fig 
aft operation is 3 thet of polifhing the fpeculum, na 
this is ithe moft difficult and effential part of the whole ita 
cefs. Mr. Mudg 
ber of tsinkic both of svg 
an exquilite polifh at the fame time. 
h 
Newton, and mentioned in his Optics, he formed his 
by coating the brafs convex tool equally with pitch, which 
fhould be neither very hard and refinous nor too foft, about 
the thicknefs of a fhilling, and by applying bruifer to. it, 
ge the pitch upon the polifher a fine furface and the true 
orm Me: the a ifer. He then divided the i weight 
upon ack of the matte into eight parts, by ftrokes on 
the re of the lead, are marked with the numbers 
ia &e. in Pin ie diftingnith and. regulate thei 
turns of the metal, He alfo put half an ounce of putt 
into an ounce phial, and filled it two-thirds with water ¢ 
and having fhaken the whole, let the putty fubfide; and 
{topped the bottle with a cork: the other appendages of 
his apparatus are a fmall-fized camel’s hair brufh in a tea- 
cup with a little water, a piece of dry clean foap.ina gal- 
ley-pot, anda foft piece of fponge. Thefe, as well as 
metal, bruifer, and polifher, fhould be conttantly ¢ overed. 
Sen uff, 
The polither being fixed down, is brufhed over with the 
camel’s hair bruth, after it has been wetted and rubbed 
a little over the foap 5 ; then the bruifer is worked lightly 
upon it, till it has acquired a good face and is fit for she 
metal. Then, having fhaken up. the put ty in the plual, 
and touched the polifher in five or fix places with the 
cork wetted with that and the water, the bruif 
upon the tool, and a few 
putty, in order to rub down any gritty particles: after 
which, having removed it, the metal is rece lightly 
upon polifher round and round, carrying the edges. 
of the ri however, not quite half an inch over 
the edge of the tool, and now and then with a crofs 
ftroke. The putty is repeatedly applied in the. Ke mane 
ope- 
ner, and wrought into the piteh in the courfe of t 
if bruifer be apt to ftick,,. and does not. 
hly upon the pitch, the furface of either tool. 
may be occalionally het over with the foap and. water. 
After fome scone Bi s, the an th is sat 
thr 
gu ‘When Ain solith of 
nearly reaches the cdgach he round ftrokes mutt be be apes 
_ When this 
done for fome time, in the ma 
tion ine 
{peedily, and. the whole furface of t 
eg w , 4 
metal iehie much, its furface muft be now and a 
with a of fhammy leather, and the 
with a foft piece of wet fponge, You ru wilo be # le to. 
