_Those Surfaces of transparent Bodies, which if the Ray be in a Fit of
Refraction do refract it most strongly, if the Ray be in a Fit of
Reflexion do reflect it most easily._
For we shewed above, in _Prop._ 8. that the cause of Reflexion is not
the impinging of Light on the solid impervious parts of Bodies, but some
other power by which those solid parts act on Light at a distance. We
shewed also in _Prop._ 9. that Bodies reflect and refract Light by one
and the same power, variously exercised in various circumstances; and in
_Prop._ 1. that the most strongly refracting Surfaces reflect the most
Light: All which compared together evince and rarify both this and the
last Proposition.