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# Title: Opticks: Or, A Treatise Of The Reflexions, Refractions, Inflexions and Colours Of Light (shelfmark Leibn. Marg. 193)
# Folio 58, page id 1677894601:0068
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# Lines: 35 recognised, mean confidence 0.91
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N
perpendicular ones arC N CO and FF CF. And is che
Force of the retracting Plane begins to act uxon che RaYS
cicher in chac Plane or ac a certain distance from ic on the
one side, and ends at a certain distance from ic on the
ocher side, and in alI places becireen those erro Limits acts
upon che Rays in Lines perpendicular ro chat ratractine
Plane, and che Actions upon the Rars ac equal distances
From che retracting Plane be cqual, and ac unequal ones ei-
cher equal or unequal accordins to any rate Whaterer:
chac motion of che Ray irhich is Parallel to che retractine
Plane wrill sutter no alteration by chac force; and thatmo-
cion irhich is perpendicular eo ir rill be alcered accordino
eo che rule oF the Foregoins Proposition. IF cheretore FOF
che perpendicular Velocier of che emergins Rar CNY vou
MC
irrite p CC as abore, chen che perpendicular Velocier
AD
ot any ocher emereins Ray CF which was FF CF, will be
equal eo the (Guare ROOC OF CD9 -
NC. 9
NOq C69. And
by Cquarins chese equals, and adding eo them the Equals
ADgandNICg---CD9. and dividing che summs by che
Equals CFg F F Fg and CC9 ] NCG, You wil have
ADC
MICq
EFq equal EO NOg. Whence AD, the Sine ot Incidence,
is EO F. F the Sinc oF Retraction, as NC eO NO, thac is.
in 2 siren ratio. And ehis Demonstration being general.
richour decermining irhiat Lighic is, or by whac kind ot
Force ic is retracted, or alluming any ching Furcher chan
chac che retracting Body acts upon che Rays in Lines per-
pendicular to its Surtace; Pcake ic to be a very conrincine
Argumene of the tuIl Truch ofchis Propolicion.