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MOTION PICTURE PHOTOGRAPHY.
The velocity at which light travels is i86,cxx) miles per second ; that is, nearly eight times the distance around the earth in one second. What increases the heat in a light source, increases the amount of light from that source, so by increasing the amount of an electric light current or energy through an electric arc light, its brightness is increased.
The size of the waves or vibrations of light varies as do the size of the ripples in a pond when stones of different size have been thrown in, but no matter what size these vibrations possess, they move forward at the same speed or velocity. The ether waves produced by a luminous body vary from 20,000,000,000,000 to 40,000,000,000,000,000 waves per second, and the wave length in ether accordingly varies from one 3,250,000th of an inch to about one 1,675th of an inch. Light waves, as they travel through ether, are all alike in every respect except that of size, and in that respect, they differ only in wave length and amplitude of vibration.
In figure one, the distance from A to B represents a ray of light traveling in the direction indicated by the arrow. The curved line represents light waves. The distance from crest to crest of a wave is the wave length. The distance from the crest and in that respect, they differ only in wave length and amplitude of the vibration.
Light waves of different lengths produce different effects when they strike a solid body. Those of the greatest wave length give the sensation of red light ; as the wave length shortens, the color changes to orange-red, then to orange, and so on through orangeyellow, yellow, yellow-green, green, greenish-blue, blue, blueviolet, and violet. Waves of shorter lengths than these cannot be seen by the eye at all, but they are still able to produce an effect upon a photographic plate. They are called ultra-violet waves, or actinic waves. There is no fixed line between actinic waves and visible waves; that is, between light which we can see and light which we cannot see, but which will have an effect upon a photographic plate, because most of the light, which we can see, also has an effect upon a photographic plate.
Actinic light simply means the light which has the strongest action upon a photographic plate, whether visible or not.
There are also light waves, which are so long that they are not visible, they are longer than the visible red rays and are called infra-red or heat waves.
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