THEORY OF COLORS. 



WHEN a ray of light meets the surface of a transparent medium, such as 

 water or glass, in a line perpendicular to that surface, it will pass through \ 

 without changing its course ; but, if it meet the surface at any oblique angle, it 

 will be bent into another direction, which will depend on the direction of the 

 incident ray, and the relative densities of the media, between which the ray 

 passes. Generally, when it passes from a less dense into a more dense medi- 

 um, it is bent toward the perpendicular drawn to the surface of the medium at 

 the point of incidence of the ray. In this deflection it does not leave the 

 plane passing through the incident ray, and that perpendicular. 



Fig. i. 



To render this more clear, let c, fig. 1, be any visible object placed on the ( 

 bottom of a vessel of water. Let c n be a ray of light passing from that ob- < 

 ject to the surface of the water, that ray after leaving the surface of the water 

 and passing into the air will not continue in the direction c n, but will take 



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