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# Title: Opticks: Or, A Treatise Of The Reflexions, Refractions, Inflexions and Colours Of Light (shelfmark Leibn. Marg. 193)
# Folio 83, page id 1677894601:0259
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3
irtrich compared together crince and ratity both this
and the lact Propolition.
P RO P. XV.
In any one and the same sort of rays emersins in ans
Anele out of any refractine surface into one and the same
medium, the interval of the folloreins fits of easy reflexion
and transmission are either accurately or very nearly, as
the Rectanele of the secant of the Anole of refraction, and
et the secant of another anole, rehose sine is the first of
L0b arithmetical mean proportionals, betreeen the sines
of incidence and refraction counted from the sine of re-
fraction.
This is manifest by the 7th Obserration.
P RO P. XVI
In several forts ofrays emeroine in equal neles out
ef any refractins surface into the same medium, the inter-
vals of the follorvine fits of easy reflexion and easy trans
mission are either accurately, or very nearlys, as the Cube-
roots of the Squares of the lenoths of a Chord, rehich sound
the notes in an Pisht, Col, la, Fa, Col, la, min Fa, Coly reit h
al their intermediate derrees ansaverins to the Colours os
those rays, accordins to the Analogy described in the se
venth Fxperiment of the second B0ok.
Chis is manifest by the 13th and r4th Obserrations.
MII 2
 dac