Opticks 1717 - Up

t;ure ‘of 2;. Inches, s about x20 tiims,
with as much diEn&nefs as OIE of a Foot in
.BengtIl; with f of an Itich aperture, magnifies
xj- times.
l\aow were it not for this different Refi-angibility
of Rays, Telekopes might be brought to
a greater perfe&ion than we have yet defcrib’d,
by compofing the ObjeA-Glafs of two (r;rla&
with Water between thcrn. Let .A.DI;‘C[in .F&”
28.1 reprelent the Obje&-glafs ~OIllpOfd of two
Glafftes ABED and BEFC, alike convex on the
outfides ACD and C I-IF, and alike concatre
on the infides-B ME, B NE, with IVater in
the concavity 13 bdEp\;T. ket the Sine of I[ncidence
out of Glafs into Air be as I to R, and
out of Water into Air as K to 14, and by COII-
Sequence out of Glafs into Water , as I to M ‘:
and let the diame of the Sphere to which the
convex iides AG and C 111 II; are ground be
D, and the dismeter of the Sphere to which
the concave fides I3 .M lei: & I3 NE are wound
be t@D, as the Cube Root of R K-K ,, t to the
Cube Root of R K---!&I: ,and the RcfiacCEions
on the concave ficles of theGMTcs, will very
much cosseA the Errors of the RckaAions on
the convex fides, fo fizr 3s they arife Corn r:hc-
Cphericalnefs of the Figure. And by this 1n~a11s
might Telekopes be brought to M~cIcI~I~ per-
%ec(tion, were it not for the difkm~t ,Ij.cft*nngibility
of Several forts of Knys. But I+ j*catbll
of this different RefrangiMity, I do not yet fee
any other means of impfov3ilGg Tclefccjpcs by
Mefia&ions alone than that of incseafing their
kngths, for which end the late Contrivance of
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