SCIENCE OF COMMON THINGS. 255 



Rivera deeper than they appear to be. Compound nature of white light. 



167*8 Why does a river always appear more shallow than it really is 1 



Because the light proceeding from the bottom of the 

 river is refracted as it emerges out of the water, and 

 causes the bottom to appear elevated. 



167*3 How much deeper is a river than it seems to be? 



About one-third. If, therefore, a river seems only 

 four feet deep, it is really six feet deep. 



Many persons get out of their depth in bathing in consequence of this 

 deception. 



The following simple experi- 

 ment illustrates the effect of re- 

 fraction: Place a silver coin, i 

 m, at the bottom of a basin, Fig. 

 68. The rays, i *, proceeding to 

 the eye from the silver surface, 

 render the coin visible. The 

 point a, the eye, is then moved 

 farther back, so that the edge of 

 the basin obstructs the direct 

 rays, and of course the coin is 

 no longer seen. If an attendant 

 carefully pours water into the 

 basin, so that the object is not moved, it will presently, as the water rises 

 in the basin, become again visible. This arises from the refraction of the 

 rays by the water, the image, indeed, appearing at n instead of at m. 



167*4 Is a ray of white light simple or compound? 



Every ray of white light is compounded of other rays 

 of colored light. 



1675 Into how many parts may a ray of light be divided f 



Into three parts : blue, yellow, and red. 



These three colors, by combination, make seven : 1, red ; 2, orange (or 

 red and yellow) ; 3, yettow ; 4, green (or yellow and blue) ; 5, blue ; 6, in- 

 digo (a shade of blue) ; and, 7, viokt (or blue and red). 



1676 How is it known that a ray of light consists of several different 

 colors f 



Because if a ray of light be cast upon a triangular 

 piece of glass (called a prism), it will be distinctly 

 divided into seven colors : 1, red ; 2, orange ; 3, yel- 

 low ; 4, green ; 5, blue ; 6, indigo ; and, 7, violet. 



1677 Why does a prism divide a ray of light into various colors f 



Because all these colors are refracted, or bent out of 

 their course differently. Red is refracted least, and 

 blue the most ; therefore, the blue ray will be bent to 



