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# Title: Opticks: Or, A Treatise Of The Reflexions, Refractions, Inflexions and Colours Of Light (shelfmark Leibn. Marg. 193)
# Folio 54, page id 1677894601:0064
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C54
Retranoibiliey, as is manifest by che sch, 6ch, 7ch, 8th,
and oth Experimenes. And chose which che Arst cime ac
like incidences arc equally retracted, arc 2rain at like In-
cidences equallr and uniformly retracted, and chac whe-
cher cher be retracted betore cher be separaced From one
anothier as in the sth Experiment, or Wwhecher ther be re-
Fracted apare, as in the 12ch, 13th and 1ath Experiments.
The Retraction cheretore oF every Ray apare is regular,
and wtrac Rule chac Retraction oblerres e are nOW
Eo TheW.
The lace Vricers in Opricks ceach, chac the Sines oF In-
cidence are in a oiven Proportion co che Sines ot Retra-
ction, 25 was explained in the sch Axiom; and lome by
Instrumenes Aicced For measurine Retractions, or ochermise
experimentally examinins chis Proportion, do acquaine us
ehat ther hare Found ic accurate. Buc Whils cher, nOc
understanding che different Retransibilier of several RayS,
conceired chem all ro bc retracted accordine to one and
che lame Proporrion, eis co be prelumed thac cher adapred
their Mealures only co the middle ot the retracted Lighe;
(o thac trom cheir Measures e may conclude only chac
che Rays irhich hare a mean deoree of Retrangibilier.
thac is chose irhich when separaced trom che rest appear
orcen, are retracted accordins to a siren Proportion ot
cheir Sines. And cheretore we are no co Phew rhac phe
like siren Proportions obtain in all che rest. Thac il
Thould be (o is very realonable, Nature being ever contor-
mable to her selF: buc an experimental Proot is delired.
And such a ProoF will be had it we can Phew thac che
Sines ot Retraction ot Rars differenely Retransible are
one to anocher in a giren Proportion irten cheir sines ot
Incidence are equal. For il the sines oF Retraction oF aII
che Raysare in giren Proportions tothe sine of Retraction