fare, or the convemefley of the place 5 and above this Frame 
let a Pin be put through the upper Pole, to hinder its getting out 
of the Circle B. and to the end that it may be raifed a little* but 
not to be made lower by the Workman. 
Or elfe, let the Pole S. be thruft into the Ball O N. {tig. |0 
movable within the two Circles P. very well fixt to the two 
arms Z Z, and let thofe two Circles be made parallel, hindring 
the Ball to get out. But the Office of thefe two Circles may be 
perform'd by one alone, but larger, in the manner of a Stckef, 
which may gird about fach a part of the circumference of the 
Ball in the middle, as not to let it flip out. 'Tis enough, if the 
Ball do but freely move in it 5 yet fo as alwayes to touch it : 
which alfo is to beobferved in the Ball with two Circles, by that 
means to keep alwayes the Center thereof, when it moves 8 juft 
irt the fame fituation. 
Let the Plain of the Iron, or other Mettal, on which the Glafs 
is to be ground (F.in.P/g'.i ) be plac'd level upon the Form G.to 
do which, I have pra&ifed the following Contrivance, Let there 
be prepared two fquare Planks of wood (FR) equally thick, long 
and broad $ but in the undermoft let there be fixed a fquare Ruler $ 
folid and firm, as long as is the thicknefs of both the (aid Planks; 
and in the upper Plank let there be a fquare hole or groove fo 
fitted, as that the Plank may fteddily Aide upon the faid Ruler % 
And to fuch Rulers (which may be called the Regulators of the 
2 # Planks') let there be made a ledge to keep the board more fted- 
dy and ftiff upon the Ruler. 
Further, let thefe 2. Planks have two Gutters (R. VJ of a 
Figure, going a crofsfrom end to end * into which may pafs two 
wooden wedges , like Y (of which may be made four, to put 
one of them againft another in the faid Gutters.) And then, when 
you will place the Plate FT. level on thefe Planks TR y take a 
Pendu!um,or other levelling Inftrument^and adapt it upon the faid 
Plate, which if it be not found level, obferve on which fide it 
leans, and adjuft it by the wedges. 
The ufe of this Instrument is very eafie, fince 'tis fufficient to 
guide with your hands the Mallet, faftned to the Pole upon the 
Plain, wherethe fand is fpread^ making fuch turns, as they ufe 
lo deeia this work 5 and continuing fo, till the Glafs has taken 
Bbbbba its 
