THE RAINBOW. 



647 



towards the earth. But the true reason of the phenomena may have to be 

 yet discovered, for nothing absolutely certain is known as to the origin of 

 the aurora. 



Amongst the numerous effects of refraction and reflection of light the 

 RAINBOW is most common and the most beautiful. If we hold a chandelier 

 " drop " in the sunlight, we shall see a brilliant representation of the rain- 

 bow on the wall or on the carpet. The three colours red, yellow, and blue 

 mingle or shade away into seven red, orange, green, blue, yellow, indigo, 

 and violet. These colours are all found in the rainbow. 



Fig. 728. Parhelia, or mock suns. 



The colour of the atmosphere the usual blue tint of the sky arises 

 from the blue rays of the spectrum being reflected more than the rest by the 

 aerial particles, and the less vapour the bluer the sky, because the vapour 

 gives it a whitish or misty tint. At sunset and sunrise the sky is red or 

 yellow, like gold, or of crimson hue. This is because the sun's rays have so 

 much farther to come to us at sunrise or sunset, as you will readily perceive 

 if you draw a line from the sun to the sides and then to the top of the arc 

 of the heavens. The blue rays are thus lost in space, while red and yellow, 

 which travel so much faster than blue, are transmitted to the eye, not 

 giving the air time to absorb them. 



