of Metals for refle£ling Telef copes. 305 
the middle, as a lodgment for the emery, of about an inch 
diameter for a metal of four inches : when this is done, 
deep grooves mult be cut acrofs its furface with a graver, 
in the manner reprefented in fig. 1. Thefe grooves 
will ferve to lodge the emery, and by their means the 
tool will cut a great deal falter. There is no occafion 
to fear any alteration in the convexity of this tool by 
working the metal upon it, for the emery will bed itfelf 
in the lead, and fo far arm the furface of it, that it will 
preferve its figure and cut the metal very fait. Any kind 
of low handle, fixed on the back of the metal with foft 
cement, will be fufiicient; but it fhould cover two-thirds 
of its back to prevent its bending. This way of working 
will cut the metal falter, and with more truth, than the 
method defcribed by Dr. smith; for fhould the fur- 
* f 
face and rough parts be attempted to be ground off by 
a common grind-ftone by hand, though you did it as 
near the gage as poffible, yet the metal would be fo 
much out of truth when applied to the fucceeding tool, 
that no time would be faved by it. I ufed to employ 
a common labourer for this purpofe, who foon acquired 
fuch a dexterity at working upon this tool, that in two 
hours time he would give a metal of four inches dia- 
meter fo good a face and figure as even to fit it for the 
hones. When all the fand-holes and irregularities on the 
face of the metal are ground off, and the whole furface 
Vol. LXVII. R r is 
