Optics

The refraction of the eye - Optics

Light is propagated from a luminous point in every plane and in every direction in straight lines; these lines of direction are called rays. Rays travel with the same rapidity so long as they remain in the same medium.

The denser the medium the less rapidly does the ray of light pass through it. Rays of light diverge, and the amount of divergence is proportionate to the distance of the point from which they come; the nearer the source of the rays the more they diverge.

When rays proceed from a distant point such as the sun, it is impossible to show that they are not parallel, and in dealing with rays which enter the eye, it will be sufficiently accurate to assume them to be parallel when they proceed from a point at a greater distance than 6 metres.

A ray of light meeting with a body may be absorbed, reflected, or if it is able to pass through this body it may be refracted.