332 Mr. mudge on Jhe ConJlruElion 
diligent, for the polifher drying, and the friction in- 
creating very fall, the bufinefs of the fpherical figure is 
nearly at an end. As the metal wears much, its furface 
mull be now and then cleaned, with a piece of fhammy 
leather, from the black fluff which collects upon it;, and 
the polifher likewife from the fame matter, with a foft 
piece of wet fponge. You will now be able to judge of 
the perfect fpherical figure of the metal and tool, when 
there is a perfect correfpondence between the furfaces, 
by the fine equable feel there is in working, which is 
totally free from all jerks and inequalities. Having pro- 
ceeded thus far, you may put the laft finifhing to this 
\ 
figure of the metal by bold crofs ftrokes, only three or 
four in the directions of each of the eight diameters, 
turning the metal at the fame time: this mull be done 
quickly, for it ought, in this part of the procefs particu- 
larly, to be remembered, that, if you permit the tool to 
grow quite dry, you will never be able, with all your 
force, to feparate that and the metal, without deftroying 
the polifher by heat. 
The metal has now a beautiful polilh. and a true 
fpherical figure, but will by no means make a fharp dif- 
tindt image in the telefcope : for the fpeculum (if it be 
tried in the manner hereafter recommended) will not be 
found to make parallel rays converge without great 
aberration ; 
