Man's physical universe

xanabras

COLORS ARE PORTIONS OF VISIBLE SPECTRUM 415

colored picture in a projector. The three films may be used to produce

three different colored prints in gelatine films, which are then superimposed

to produce a colored photograph. Or the three films may be

used to produce three different photoengravings, the blue one being

used with blue ink, the red one with red ink, and the yellow one with

yellow ink, each color being superimposed on the other to produce the

colored printing with which we are familiar.

In order to transmit a colored photograph over a telephone wire, the

colored photograph is first broken down into three elemental prints,

blue, red, and yellow. Three black-and-white negatives are made of

these prints, and they are fastened with their axes in parallel on a

drum, which is scanned by an "electric eye" line by line in a direction

transverse to the parallel axes as the drum is rotated. The "electric

eye" produces an electric current that fluctuates in correspondence to

the shading of the prints. This electric current is transmitted over a

telephone wire to the receiving station, where corresponding prints

are produced by a similar scanning device that changes the fluctuating

electric current into a fluctuating light. The three prints thus obtained

are used to produce photoengravings for color printing.

Complementary Pigment Colors Produce Gray Light by Addition.

Complementary colors consist of pairs of colors which, when mixed,

will give gray light. One method of determining complementary colors

is based on the principle of retinal fatigue, mentioned above.

If a circle

of red paper, strongly illuminated by white light, is gazed at intently

for about thirty seconds and is then replaced by a sheet of white paper,

a bluish-green circle will appear to take the place of the red. The

retina becomes fatigued by the red so that when acted on equally by all

colors, it responds more strongly to the remaining colors in the spectrum.

The red and bluish-green are complementary. Any one of the

three primary pigment colors will produce its complementary color

in the same manner. Complementary colors may also be determined

by blending colors on a color wheel. Some other complementary color

combinations are: orange and blue, yellow and blue-violet. In each

of these cases the color is a primary color, and its complement is a

result of a mixture of the other two primaries.

Blackouts May Employ Complementary Lighting.

By the use of complementary lighting, windows may be treated so

that they will not permit artificial light to show through them at

night but will

permit the sunlight to shine through them in the daytime.

The windows are covered with blue filters which will not pass

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