30 6 Mr. mudge on the ConJlruSUon 
is fmooth and regularly figured, the fpeculum is then 
ready for the brafs grinder, and muft be laid afide for the 
prefent. 
'The manner of forming the brafs-grinding tool. 
The following is the method I have always purfued. 
Procure a round flout piece of Hamburgh brafs, at 
molt a fixth part larger than the metal to be poliilied ; 
and let it be well hammered into a degree of convexity 
(by the affiftance of the gage) fuitable to the intended 
fpeculum. Having done this, fcrape and clean the con- 
cave fide fo thoroughly that it may be well tinned all 
over ; then caft upon it, after it has been prefied a proper 
depth into the fand, the former cornpofition of tin and 
lead, in fuch quantity, that it may (for a fpeculum 
of four inches diameter) be at leaf! an inch and an half 
thick, and with a bafe confiderably broader than the top, 
in order that it may ftand firmly upon the bench in the 
manner hereafter to be defcribed. This being done, it 
muft; be fixed and turned in the lathe with great care, 
and of fuch a convexity as exactly to fuit the concave 
gage, which we fuppofe already made. It will be necef- 
fary to be more careful in forming this than the former 
tool, and efpecially that no rings be left from the turning; 
nor 
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