of Metals for refleSling T’elef copes. 345 
that is perfectly well calculated for the purpofe ; for at 
the fame time that it is foft enough to fuffer the putty to 
lodge very freely on its furface, and for that reafon to 
4 
give a moft tender and delicate polifh ; it is likewife 
totally inelaftic, and therefore never, from that princi- 
ple, fuffers any alteration in the figure you give it. If 
the firft makers of the inftrument, therefore, had given 
proper credit to, or had limply followed the hint Sir 
Isaac gave, it would have faved them infinite trouble, 
and they would have produced much better inftruments ; 
but the pretended refinement, of drawing a tin&ure 
from pitch with fpirits of wine, affords you only the re- 
dinous, hard, and untraftable part of the pitch, divefted 
of all that part of its original fubftance which is necelfary 
to give it that accommodating pliability in which its 
excellence confifts. 
It is needlefs to fwell this account with a detail of the 
procefs for polilhing the little fpeculum, as it mull be 
N»4 
conducted in the fame manner which has been already 
defcribed in that of the large one; only obferving, that 
as the little metal has an uninterrupted face, without a 
hole, fo there is no occafion for one in the polifher; and 
likewife that, as a fpherical figure is all that need here be 
prattically attempted, fo the difficulty in finifhing is infi- - 
nitely ffiort of that of the other. 
Vol. LXVII. Y y 
As 
