Mr. mudge on the Conjlruftion 
flight blow, the pitch immediately feparates, and the 
handle drops off; the remaining pitch may be fcraped 
oflF with a knife, taking care that none of the dull flick 
to the polifhed face of the metal. 
Having placed the fpectilum in the cell of the tube, 
and directed the inftrument to the object, make an annu- 
lar kind of diaphragm with card-paper, fo as to cover a 
circular portion of the middle part of the metal between 
the hole and the circumference, equal in breadth to about 
an eighth part of the diameter of the fpeculum : this 
paper ring fliould be fixed in the mouth of the telefcope, 
:and remain fo during the whole experiment, for the part 
of the metal covered by it is fuppofed to be perfect, and 
therefore unemployed. 
There muft likewife be two other circular pieces of 
card-paper cut out, of fuch fizes, that one may cover the 
center of the metal by completely filling the hole in the 
daft defcribed annular piece ; and the other, fuch a round 
piece as fhall exadtly fit into the tube, and fo broad as 
that the inner edge may juft touch the outward circum- 
ference of the middle annular piece. It would be con- 
venient to have thefe two laft pieces fo fixed to an axis 
that they may be put in their places, or removed 
from thence fo eafily as not to difplace or lhake the 
3 .inftrument. 
