Chapter 3

On Refraction.

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

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.