Opticks 1717 - Up

to flick fi~ii. iii the Pitch, they would by r01hg
11~ alld down grate and fret the ~~bje&?&tal
and fill it f~111 of little holes.
Rut becaufc Metal is more difhcu1.t to polifh
thau CJafss and is afterwards very apt to be
* fpoiled by tarniihing, and rcfle& nat fo ~mzh
Light as Glafs quick-filver’d OVCY &XS; I Lvould
propound to ufe infiead of the .Mctal, a, GM’s
graund CQIIC~+VC on the for&de, and as much
convex 011 the back-fide,, and quick-filve?d o-
ver 011 the convex fide. The Ghfi IIILG be CT&
very wllcr& of the film thkkncfs cXlAly. O-
therMrife it will make O~~CAS 100k COIOLW’CI and
jl&fiin&. Ry filch a a& I tried about five or
fix Years yjo to make a refle8ing Telcfcope of
four Feet in, l.ength to magnify about ‘F $0 times,
and I fatisfied my felf that there mnts nothii~g
but a good Art8 to bring the Ikfign to per-Fe-
Aion. For the Glafs being wrought by one of
our .Lom!on Attiits after fuch a manner as they
grind Glaires for Telefccopes, tho’ it feemed as
well wrought as the Object-glaKes ufe to be, yet
when it was quick-filver’d, the Reflexion dig
covered innumerable Inequalities all. over the
Glafs. And by reafon of thefe Inequnlitics, Obje&s
appeared indiitin& in this Inilrcment~, For
the Errors of refleAed ‘Rays caukd by ally Ingquality
of the C-1 I a E s, are about fix times grcata
er than the Errors of refktk’ed Rays cnuicd by
he like Tncqualitks. Yet by this Experiment
fatisfied my felf that the Reflexion on rhe
concave fide of the Glafs, which I feared would
difturb theVifion, did,no fenfiblc prejudice to
it, and by confequence that nothing is’ wanting
tG,