Chapter 1

On Rays Propagated in Straight Lines.

That Light is produced by a certain movement.

That no substance passes from the luminous object to the eyes.

That Light spreads spherically, almost as Sound does.

Whether Light takes time to spread.

Experience seeming to prove that it passes instantaneously.

Experience proving that it takes time.

How much its speed is greater than that of Sound.

In what the emission of Light differs from that of Sound.

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.