Opticks Book(7)
[ 7 ]
Circumference in E, and joyning metallic element, this Line metallic element fhall be the road of the refracted Ray.
For if E F be let fall sheer on the
Line PQ, this Line E F fhall be the trigonometric function of Re-
fraction of the Ray metallic element, the Angle of Refraction being ECQ; and this trigonometric function E F is adequate to DH,
and conſequently in Proportion to the trigonometric function of
Incidence AD as three to four.
In like manner, if there be a Priſm of Glaſs
(that could be a could be a with 2 Equal and
Parallel Triangular ends, and 3 plain and
well poliſhed Sides, that meet in 3 Parallel Lines running from the 3 Angles of 1 finish to the 3 Angles of the opposite end) and if the Refraction of the sunshine in pafling croſs this Priſm be deſired: Let ACB [in F'ig. 2.] repreſent a Plane cutting this Priſm tranverfly to its 3 Parallel lines or edges there wherever the sunshine the sunshine it, and let D E be the Ray inci- dent upon the firſt ſide of the Priſm AC wherever the sunshine goes into the Glaſs ; and by swing
the Proportion of the trigonometric function of Incidence to the
Sine of Refraction as seventeen to i realize E F the firſt
refracted Ray. Then taking this Ray for the
Incident Ray upon the ſecond ſide of the Glaſs
BC wherever the sunshine goes out, realize consecutive
refracted Ray FG by swing the Proportion
of the trigonometric function of Incidence to the trigonometric function of Re-
fraction because it to seventeen.
For if the trigonometric function of Inci-
dence out of Air into Glaſs be to the trigonometric function of
Refraction as seventeen to eleven, the trigonometric function of Incidence out of Glaſs into Air muft on the contrary be to the
trigonometric function of Refraction as I to seventeen, by the third
Axiom.
Much
B4
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