Opticks 1717 - Up

Circumference in E ynifig C E, this Line
CE fix111 be the Line. of the refraCted Ray.
For if EF be let--fall perpendicularly on the’
I.,ine I? Q,. this Line E F ihall be the Sine of RefraAion
of the Ray C E, the Angle o.fRefraAion
being EC Q ; and this Sine E 13’ is e@al to 2) I-3,
and confequently in Proportion to the Sine of
Incidence ikD as 3 to &. ’ i
Jn like manner, if there be a Pri%m of Clafs
(that is a Glafs bounded with twio Equal and
Parallel Triangular ends, and
well polifhed Sides, which meet
Lines running from the three
end to the three Angles of the
he RefiaAion of the Light in paffing crofs this
fm be dedired : Let AC B [in Fig. 2.1 reprefent
a Plane cutting this Prifm tranfverfly to its three
Parallel lines or edges there where the Light
paireth through it, and let DE be the Ray incident
upon the.fXI fide of the Prifm A C whez:e
the Light goesinto the Glafs ; and by puttmg
the Proportion of the Sine of Incidence to the
SSine of RefiaAion as 17 to 91 find E F the
d Kay. Then taking this Ray for the
yupon the fecond fide of the Glafs
.BC where the Light goes out, find the next
refraAed Ray.. F G by putting the Proportion
of the Sine of Incidence to the Sine of Rejl
fraAion as P I to 17. For if the Sine of Inci-.
dence out of, Air into Glafs be to the Sine of
RefraAion as 17 to I I, the Sine of Incidence out
of Glafs into Air mui% on the contrary be to the
Sine of Refraftion as II’ to 17, by the* thijd
p,Axiom. :, ’
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