How consequently some objects appear higher than they are.

How the Sun may appear on the Horizon before he has risen.

That the rays of light become curved in the Air of the Atmosphere,
and what effects this produces.

CHAPTER V.
On the Strange Refraction of Iceland Crystal.

That this Crystal grows also in other countries.

Who first-wrote about it.

Description of Iceland Crystal; its substance, shape, and properties.

That it has two different Refractions.

That the ray perpendicular to the surface suffers refraction, and
that some rays inclined to the surface pass without suffering
refraction.

Observation of the refractions in this Crystal.

That there is a Regular and an Irregular Refraction.

The way of measuring the two Refractions of Iceland Crystal.

Remarkable properties of the Irregular Refraction.