Chapter 12 — THE GOVERNING FUNDAMENTALS OF METEOROLOGY 



Now consider this same light ray entering 

 a denser medium at an oblique angle. That 

 portion of the wave front which first enters 

 the water moves slower than the other part of 

 the wave front which is still in the air; con- 

 sequently, the ray will bend. (See fig. 12-19.) 

 Notice that the light ray bends toward the 

 normal. 



If the light ray entered a LESS dense 

 medium at an oblique angle, the ray would 

 bend away from the normal as illustrated in 

 figure 12-20. The portion of a wave front which 

 enters the less dense substance travels faster 

 than the other part of the wave front;consequently, 

 the ray bends away from the normal. 



When a beam of white light is passed through 

 a prism, as shown in figure 12-14, itis refracted 

 and dispersed into its component wavelengths. 

 Each of these wavelengths reacts differently 

 on the eye which then sees the various colors 

 that compose the visible spectrum. 



The visible spectrum is recorded as a mix- 

 ture of red, orange, yellow, green, blue-green, 

 blue, indigo, and violet (fig. 12-14). Some texts 

 may list only the six simple colors of red, 

 orange, yellow, green, blue, and violet. 



NORMAL 



AIR 



mm 



, .WATER 



\ 



Wmm 



■MMMMi^ 



I 



209.20 

 Figure 12-19. — Wave front diagram illustrating 

 refraction of light at an air-water boundary. Ray 

 is entering a more dense substance. 



\ 



NORMAL 



209.21 

 Figure 12-20. — Wave front diagram illustrating 

 refraction of light at an air-water boundary, Ray 

 is entering a less dense substance. 



ATMOSPHERIC OPTICAL 

 PHENOMENA 



We think of atmospheric optical phenomena 

 as those phenomena of the atmosphere which 

 can be explained in terms of optical laws. 

 Given below is a description of some of the 

 optical phenomena which we commonly observe. 

 Some of the atmospheric elements, such as 

 moisture, serve as a prism to break a light 

 source down into its various component colors. 



Mirages 



A mirage is an optical illusion due to the 

 refraction of light as it passes through non- 

 homogeneous layers of the atmosphere. Distant 

 objects are seen in an unnatural position, 

 sometimes elevated, sometimes depressed, and 

 often inverted; this phenomenon occurs most in 



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