Opticks 1717 - Up

Inay be aIfo dcge b compofig ,the $peculpm
of LW~O C$Kes \xrith b ater betwepn .them.
If the’Theory of making ?‘elefcopes c,ould at
~lel~g~hbg,*fulIy brought into prdice, yet: ther
:would ,lj certain Bpunds beyond ~!uch Tcle-
Scopes could not perform. For the +r through
6 wllich. we lock upon the Stars, is ~1 a perpet&
‘J’re.ir&r; as may be ken by the tremulous
‘Motion of Shadours cait: fiotn hig$ To~crs,
and q by ilie- tv&&ling ,06 the fix’d Stars. &t
th& Stars do not twinkle When VWV~ t-hrough
“Tel&copes which have large ~~UUKS. +‘or
the Rays of Light which pafs through divers
partzs of the aperture, t;embk J e~h f. - of - the: ;- 1
parr, ‘and by means of their various and fometim?s
contrary Tremors, fall at one and the
fame time upon di&rent points in the bottonl
of the Eye, and their trembling Motions are too
quick and confukd to be perceived fcverally.
And all thefe illuininated Points conititute one
broad lucid ‘Point, compokd of thol’e many
tqembling ‘Points confufedly and infcnlibly mixed
with one another by very fl~ort and fwi.f;
Tremors, and thereby caufe thd Star to appear,
broader thall it: is, and without any trembling
of the whole. LongTelefcopcs may cau.fc QbjeAs
to appear brighter and larger than ihort
ones. can do, but they cgnnot be i’o formed as
PO t&c aWay that c011fufio11 of the Rays which
arifes from the Tremors of the Armoi’phere.’
73x2 only remedy is a moit ferene and quiet Air,
Such as majr perhaps be .found on the tops of
the highcNI%ountains above the groiltr Clouds.