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incidence increases (by letting fall its ray more obliquely) the
angle of refraction does so too. Hence before the ray of inci
dence falls parallel to the surface of the water, the ray of re
fraction (its angle being greater) must immerse in the water and
because now both rays are within the water refraction is chang
ed into reflection. As soon as the ray of refraction travels
through water, light is reflected according to the ordinary laws
of reflection. This kind of reflection is called total (or in
ternal) refection, because in this case the whole of the incident
light is reflected.
§ 194. The different layers of air have a different density
especially over a very much heated soil. The least dense layers
are then the lowest and luminous rays, whilst passing through
these layers of air, the angle of incidence will more and more
increase. The total reflection of the rays, which must take place
at the beginning, finally will become refraction (the incident
angle having become small enough) and the object will be seen
in the continuation of the final direction of the ray reaching our
eye, which means: we see it as if below the ground or as if in
the atmosphere. An inverted image above the objects will
appear, if the upper layers of the air are thinner than the lower
ones, otherwise the image will be below the subjects. In this
case the rays of light passing through layers of less density, the
angle of refraction will increase to such a degree that ultimately
refraction will succeed to internal reflection, This phenomenon
is called mirage (thus a tranquil lake, trees and villages may
be seen in a desert). Similar images are produced on the sea.
But these occur only if the temperature of the air is higher than
that of the sea, hence the layers below are denser. This
phenomenon we call Fata morgana. By the unequal density
of the different layers of the air also the following is caused;
