fall obliquely, it is bent from its direct course and recedes from it,
either towards the right or left, and this bending is called refraction;
(see fig. 3, b.) If a ray of light passes from a rarer into a denser medium
it is refracted towards a perpendicular in that medium; but if it passes from
a denser into rarer it is bent further from a perpendicular in that medium.
Owing to this bending of the rays of light the angles of refraction
and incidence are never equal.

Transparent bodies differ in their power of bending light--
as a general rule, the refractive power is proportioned to
the density--but the chemical constitution of bodies as well
as their density, is found to effect their refracting power.
Inflamable bodies possess this power to a great degree.

The sines of the angle of incidence and refraction (that is,
the perpendicular drawn from the extremity of an arc to the diameter
of a circle,) are always in the same ratio; viz: from air into water,
the sine of the angle of refraction is nearly as four to three,
whatever be the position of the ray with respect to the refracting surface.
From air into sulphur, the sine of the angle of refraction is as two to one--
therefore the rays of light cannot be refracted whenever the sine
of the angle of refraction becomes equal to the radius* of a circle,
and light falling very obliquely upon a transparent medium ceases
to be refracted; this is termed total reflection.

* The RADIUS of a circle is a straight line passing from the centre
to the circumference.

Since the brightness of a reflected image depends upon the quantity of light,
it is quite evident that those images which arise from total reflection