Proof that the ethereal matter passes through transparent bodies.

How this matter passing through can render them transparent.

That the most solid bodies in appearance are of a very loose texture.

That Light spreads more slowly in water and in glass than in air.

Third hypothesis to explain transparency, and the retardation which
Light suffers.

On that which makes bodies opaque.

Demonstration why Refraction obeys the known proportion of Sines.

Why the incident and refracted Rays produce one another reciprocally.

Why Reflexion within a triangular glass prism is suddenly augmented
when the Light can no longer penetrate.

That bodies which cause greater Refraction also cause stronger
Reflexion.

Demonstration of the Theorem of Mr. Fermat.

CHAPTER IV.
On the Refraction of the Air.

That the emanations of Light in the air are not spherical.