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# Title: Opticks: Or, A Treatise Of The Reflexions, Refractions, Inflexions and Colours Of Light (shelfmark Leibn. Marg. 193)
# Folio 5, page id 1677894601:0015
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25 17 20 11. In Lighe ot orher Colours the sines have
ocher Proporrions: buc che difference is (o licele chat it
necd seldom De consdered.
Suppose theretore, that R S reprelents the surtace oF Fig. P.
Ragnaring Wacer, and C is che point ot Incidence in
irhich any Ray comins in che Air trom A in che Line
AC is reflected or retracted, and I vould know irhether
ehis Ray Phall g0 atter ReAerion or Retraction: I crect
uxon che surtace of che Water trom the point ot Inci-
dence the Perpendicular C P and produco ic donmards
t0, and conclude by che Airst Axiom, thac che Ray af-
cer Rellexion and Retraction, Phall be Found Comerhere in
che Plane ot che Angle of Incidence AC P produced.
lec Falt cheretore uxon che Perpendicular C P the sine ot
Incidence AD, and it che reftected Ray be delired, Ipro-
duce AD eo B (0 thac D B bC equal tO AD, and dram
CB. For chis Line C B Phall be the reffected Ray; the
Angle ot Rellexion B C P and ies Sine BD being equal
co che Angle and sine ot Incidence, as ther oughe to bc
by che second Axiom. Bur it che retracted Ray be de-
sired, Iproduce AD eoTI, (0 that D II may BC EO ALd
as the sine ot Retraction to che sine ot Incidence, thac is
25 3 c04; and abouc che Center C and in the Plane A C P
wich the Radius C A describing a Cirele AB F I draw
Parallel cothe Perpendicular C P C, the Linc HP cuctine
the circumterence in F, and jorning CP, chis L inc C F
Pail be che Line of che refracted Ray. For iFP, F BC lec
fall perpendicularty on the Linc P C, this Line P F Phalb
De che sine ot Retraction of che Ray CF, che Angle oF
Retraction being P C (; and chis sine F F is equal eo
DII, and consequencr in Proporrion ro the sine of inci
dence A D a5 310 A.