34 a Mr. mudge on the Conjlru&ion 
or the cold of winter: in the latter, it may he poffible to 
% 
remedy the defedt by having the room warmed with a 
Itove ; and in the fummer, the other inconvenience may 
perhaps be avoided by ufing a harder kind of pitch ; but 1 
much doubt in either cafe whether the work will go on 
fo kindly : I have myfelf always wrought in fpring and 
autumn. 
The procefs of polifliing, and indeed grinding upon 
the hones, will not go on fo well if it be not continued 
uninterruptedly from beginning to end ; for if the work 
of either kind be left but for a quarter of an hour, and 
you then return to it again, it will be fome time before 
the tool and metal can get into a kindly way of working; 
and till they do, you are hurting what was done be ore. 
I have all along fuppofed that the metal we 1 Lave been 
working was about four inches diameter : if it be either 
larger or fmaller, the lizes of the hones, bruifer, and po- 
lifher, muft be proportionably different. I never find any 
ill confequence arifing from the different expanfion from 
heat and cold in any of the tools, though they be made of 
different metals and fubftances, unlefs the inconvenience, 
occafioned by the interruption before h inted at, be thought 
to refult from thence ; for the alteration produced in the 
furface of the fpeculum, both by grinding and polifliing, 
is fo much quicker than any that can be fuppofed to arife 
from 
