[From: Light and Color, by Clarence Rainwater, Prof. of Physics, San Francisco State College, Original Project Editor Herbert S. Zim, Golden Press, NY, Western Publishing Company, Inc., 1971.]
A ray of light entering the eye passes through the transparent cornea, the aqueous humor, the lens, and the vitreous humor. All help focus the light before it strikes the rods and cones, which are photoreceptors located on the retina. Here is where the actual process of seeing begins. The greatest bending of light rays occurs at the first surface of the cornea.
A group of ligaments and muscles automatically control the shape of the lens to bring objects at different distances into focus on the retina. This process is called accommodation. As one gets older, the lens gradually loses it flexibility, and the ability to accommodate decreases. [p. 84]
The human eye is the most versatile of al radiation detectors. Within the retina of the eye a chemical response to radiation is translated into electrical pulses. These very weak electrical messages travel almost instantaneously to the brain along the optic nerve fibers. The sensation of sight occurs in the brain. Because of psychological factors, the quality of visual sensations cannot be translated into physical data and there is no way to compare the visual sensations of different people with accuracy. What you see is for the most part subjective--wholly within the mind, and therefore usually not measurable. [p. 90]
[Light and Color, by Clarence Rainwater, Prof. of Physics, San Francisco State College, Original Project Editor Herbert S. Zim, Golden Press, NY, Western Publishing Company, Inc., 1971.]
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