_Rays of Light_, if not disturbed, move in straight lines, and hinder
not one another’s motions, 168.
Are refracted in passing through different mediums, 171.
_Reflection of the Atmosphere_ causes the Twilight, 177.
_Refraction of the Atmosphere_ bends the rays of light from straight
lines, and keeps the Sun and Moon longer in sight than they would
otherwise be, 178.
A surprising instance of this, 183.
Must be allowed for in taking the Altitudes of the celestial bodies,
_ib._
_Right Sphere_, 131.