THE BEASON WHY. 115 



** And it shall come to pass, when I bring a cloud over the earth, that the bow 

 shall be seen in the cloud." GENESIS IX. 



486. WTiat causes the rainloiv ? 



The refraction of the sun's rays by the falling rain. 



487. Why does the rainbow exhibit various colours ? 



The colours belong to the elementary rays of light ; and these 

 rays having different degrees of refrangibility, some of them are 

 bent more than ethers ; they are therefore separated into distinct 

 rays of different colours. 



488. Why are there sometimes two rainbows ? 



Because the rays of refracted light, reflected upon other drops 

 of rain, are again refracted, and then reflected again, forming a 

 secondary bow. 



489. Why are the colours of the secondary bow arrayed in 

 the reverse order of the primary bow ? 



Because the secondary bow is a reflection of the primary bow, 

 and, like all reflections, is reversed. 



490. Wliy are reflections reversed ? 



Because those rays which first reach the reflecting surface are 

 the first returned. If you hold your open hand towards the 

 looking-glass, the light passing from the point of your finger will 

 reach the reflector and be returned before the rays that pass from 

 the back parts of the hand. Hence the image of the hand will 

 present the reflection of the finger point towards the point of the 

 finger. 



491. Why are the colours of the - secondary rainbow 

 fainter than those of the primary ? 



Because they are derived from the refraction and reflection 

 of rays which have already been refracted and reflected, and 

 thereby their intensity has been diminished. 



492. What is a lunar rainbow f 



A lunar rainbow is caused by the light of the moon, in the 

 same manner as tts solar rainbow is caused by the light of the 

 sun 



