Opticks 1717 - Up

8
be to the Sine of Refrafiion as I to R : the Rays
which come parallel to the Axis of the Glafs,
fllall in the place where the Image of the CbjeA
is In& &fiinCtljr made, be fcattered all over a
#i7 *
little Circle ~hofe diameter r’s iI x $ very.
c .
nearly, as.1 gather by computing the Eirrors of
the Rays by the method of infimte~,~erres, and
rej&ing the Terms whofe Quantrties are inconfiderabled
As for inilancs, if the Sine of
Incidence I4 be to the Sine of Refrac%on R, as,
20 to 313. and if D the diameter of the Sphere
to which the convex fide of the Glafs is ground,
be xoo Feet or 1200 Inches, and s the iemidia-S
meter of the Aperture be two Inches, the dia-
., R-L: :t Y cd.
meter of the little Circle (that .K ,qizTqq ) w7i11
y%~rxX
‘be --( Of
ZC%ZO x 1200 x 1200
$E&) ~ parts of 911 hch..
But the diameter of the Iittlc Circle *through
which thefe Rays are icattered by unequal Red
frangibility, kill be about the 55th part of the
Aperture of the Objefl-glafs which hcrc is four
Inches. And therefore the k’~ror arifing from
the fpherical Figure o? the Flak, is to the Krror
arifing from the diflerent Kcfrangibiliry of
961’
he Rays, as so= $0 & that is as;x to f+Lt9;:
and therefore being in comparifou fo ver; little,
deferves not to be contidered,
But you will iky, if the Errors caufed by the
different Refrangibility be fo very .grcnt, how
comes it to gafs tlyat Ob&je&s a pear through
Telefcopcs, fo diitinCZ as they do, 7 I anfwer, ‘tis
2
becaufe