Man's physical universe



reflected within raindrops, each ray of hght being bent in

Drop in

Position 3

How a rainbow is produced.


to its frequency as in the case of prisms. Secondary rainbows are produced

when light is twice reflected within the drops. In the secondary

rainbow it will be noticed that the colors are reversed. No two observers

see the same rainbow, because the

rainbow seen by any individual is

produced by only those drops which

are in

the proper position relative

to the eyes of the individual.

It is possible to see the entire

circle of a rainbow from an airplane

provided that the sun is behind the

observer and the elevation is not

too great.

Circles of light sometimes seen

around the sun or moon are called

halos. Halos are red on the inside

and shade off to a pale yellow color

on the outside. They are formed

by the refraction of light by minute

ice crystals.

The color of an object depends upon the wave length of the light

which reaches the observer after the light has passed through or has

been reflected from the object. Colored materials produce color by

the absorption of all colors except the ones seen. White objects absorb

less light than black objects.

Substances show their natural colors (i.e., the colors which they

exhibit in sunlight) only when illuminated by white light. When

artificial light which is deficient in certain wave lengths is used to

illuminate objects, those colors which are missing cannot be reflected.

Thus a red cloth appears black in the light from a mercury-vapor lamp

because this light does not emit red rays.

The Normal Eye Has Three Types of Color Receptors.

The ear can recognize a mixture of the dififerent frequencies of sound,

but the eye is incapable of analyzing the components of light. No one

would ever guess that sunlight is a mixture of colors if it could not be

separated into its component hues by prisms, raindrops, or other means.

There are three types of receiver cells in the eyes. The sensation

of color depends upon the relative

receivers to the light which enters the eye.

responses of these three types of

If any one of these types

of receiver cells does not function properly, color blindness is the

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