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ami of the fame radius of concavity ; its being truly 
turned on a lathe will be fufficient for this purpofe ; 
which topi is to ferve afterwards for the polilhing of 
the two furfaces of your objed glafs, and therefor^ 
called the polilhing tool. 
Prepare a piece of draw-coloured glafs, of the 
plate glafs kind, of the proper diameter for the objed 
glafs you defire, which ought always to be broader 
than the proper aperture for that length; let this 
piece of glafs be ground flat, in another tool, on both 
lides, and as nearly parallel as may be, and fome- 
what pollflied, in order to difcover whether there are 
any veins or flaws in the glafs. When you are fa- 
tisfied of the goodnefs of the glafs, you are then to 
prepare a handle to faflen your glafs to. Great care 
miifl: be taken in this, for fear of bending your glafs 
by the handle ; my method is this ; I take a flat 
piece of brafs, or rather of the concavity of the 
fphere, to which the glafs is to be ground ; this piece 
of brafs fl^ould not be thicker than ^ of the thicknefs 
of the glafs, of a circular form, lefs in breadth fome- 
what than the glafs itfelf, and having fides of the 
fame form, at right angles to the flat piece of brafs, 
and thefe fides ought to be of fuch a diape as that 
the fingers may eafily apply to it in working, and 
thefe Tides fhould be as low as may conveniently be, 
and no thicker than about of the glafs. This 
handle is to be faffcned to the glafs, by warming the 
glafs and handle gently before a nre, and laying fume 
pitch upon the glafs thus wanned, till it becomes 
loft like melted wax ; and then laying ycur brafs 
handle, a little heated, on the pitdi, you prefs it a 
little, till you are fure there is nothing between the 
glafs 
