THE ANALYSIS OF LIGHT. 



Zoo 



What are the 

 conditions nec- 

 essary in order 

 to see a rain- 

 bow? 



Bame 

 seen 

 alike byallper- 



EOUS? 



The rainbow can be seen only when it ruins, 

 and in that point of the heavens which is op- 

 posite to the sun. 

 Hence a rainbow is always observed to be situated in the 

 west in the morning, and in the east in the alternoon. 



It is also necessary for the production of a rainbow 

 that the height of the sun above the horizon should not 

 exceed forty-two degrees. 



Hence we generally observe this phenomenon in the morning, or toward 

 evening ; and it is only in the winter, when the sun stands very low, that tho 

 rainbow is sometimes seen at hours approaching noon. 



Is the Bame '^^ ^^® ^'^-^^ °^ ^^^'^* differ greatly in refrangibility, only a 

 rainbow seen single and different-colored ray from each drop will reach tho 

 eye of a spectator ; but as in a shower there is a succession 

 of drops in all positions relative to the eye. the eye is en- 

 abled to receive the different-colored 

 rays refracted at different inclina- 

 tions. This is clearly illustrated in 

 Fig. 270, in which S represents 

 rays of the sun falUng upon suc- 

 cessive drops, E, 0, Y, G, B, I, Y ; 

 but a single colored ray, and a 

 different one for each drop, will 

 reach the eye. As no two spec- 

 tators can occupy exactly the same 

 position, no two can see the same 

 color reflected from the same drop ; 

 and consequently no two persons see the same rainbow. 



In the formation of a rainbow each colored ray reflcctea 

 bowTcircuUrT' '^°™ ^^ falling drops of rain, enters the eye at a different inclin- 

 ation or angle. But the several positions of those drops, 

 which alone are capable of reflecting the same color at the same angle, to 

 the eye constitute a circle, — and hence the bands of color which make up a 

 rainbow, appear circular. 



What are pri- Two Tainbows are not unfrequently observed 

 ^'dTr/"^!^- ^t t^^6 same time, the one being exterior to, 

 ^"^^^ and less strongly developed than the other. 



The inner arch, which is the brightest, is called the pri- 

 mary bow, and the outer, or fainter arch, the secondary 

 bow. The order of colors in the inner bow is also the* re- 

 verse of that in the outer bow. 



