That it is not the same medium which serves for Light and Sound.

How Sound is propagated.

How Light is propagated.

Detailed Remarks on the propagation of Light.

Why Rays are propagated only in straight lines.

How Light coming in different directions can cross itself.

CHAPTER II.
On Reflexion.

Demonstration of equality of angles of incidence and reflexion.

Why the incident and reflected rays are in the same plane
perpendicular to the reflecting surface.

That it is not needful for the reflecting surface to be perfectly
flat to attain equality of the angles of incidence and reflexion.

CHAPTER III.
On Refraction.

That bodies may be transparent without any substance passing through
them.