of Metals for reflecting T ’elej 'copes. 309 
likewife, its diameter ought to be the middle fize be- 
tween the hones and the polilher. 
Having with the lathe roughly formed the convex 
brafs grinder, the bed of hones, and the concave bruifers, 
the convex and concave brafs tools and the metal muft 
be wrought alternately and reciprocally upon each other 
with fine emery and water, fo as to keep them as nearly 
to the fame figure as poffible, in order to which fome 
walhed emery muft be procured. This is beft done by 
putting it into a phial, which muft be half filled with 
water and well fhaken up, fo that, as it fubfides, the coarfeft 
may fall to the bottom firft, and the fineft remain at the, 
top : and whenever frefh emery is laid on the tools, the 
beft method (which we fhould alfo obferve with the 
putty in polifhing) will be, to fhake gently the bottle., 
and pour out a fmall quantity of the turbid mixture. 
Of grinding the fpeculum , the brafs tool , and the bruifer 
together. 
All the tools being ready, upon a firm poft in the 
middle of a room, you are to begin to grind the brafs con- 
vex tool with the bruifer upon it, working the latter crofs- 
ways, with ftrokes fometimes acrofs its diameter, at others- 
a little to the right and left, and always fo fliort that the 
bruifers 
