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# Title: Opticks: Or, A Treatise Of The Reflexions, Refractions, Inflexions and Colours Of Light (shelfmark Leibn. Marg. 193)
# Folio 50, page id 1677894601:0226
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PROP. +o
Those superficies oftransparent Bodies reflect the rreatest
quantity of Lisht, rehich have the oreatest refractino porver;
that is, rehich intercede mediums that differ most in their
refractive densities. And in the confines of equally re-
fractine mediums thereis no reflexion.
The Analosy betreen reflexion and retraction will
appear by considerins, that irhien Listit passeth ob-
liquelr out ot one medium into another irhich retracts
from the perpendicular, the greater is ditference ot
their retractire density, the lels obliquity is requisite
to cause a total retlexion. For a5 the Sines arc irtrich
measure the retraction, (0 is the sine ot incidence at
ertrich the total reflexion begins, to the radius of the
Cirele, and consequentlr that incidence is least irhere
there isthe oreatest ditterence et the Sines. Phus in the
palsins oF Light out oF Water into AIr, Where the
refraction is mealured by the Ratio oF the Sines 3 t0 4,
the total retlerion begins wrhen the Angle ot incidence
is about 48 degrees 35 minutes. In passins out oFCila(s
into Air, irhere che retraction is meatured by the Ratio
OF the Sines 20 t0 3r, the total rellexion begins erten
the Anele oF incidence is 40 deg. 10 min. and (0 in
passins out oF crystal, or more sronely refractinq me
diums into Air, there is Aill a less obliquity requisite
to cause a total reslexion. Superticies theretore irhich
retract most do (oonest refleet aII the Lioht which is in
cident on them, and (o must be allored most Atrongly
xet exIre.
BUC