86 SCIENCE OF COMMON" THINGS. 



Eeft uigibility of light Red clouds at sunrise and sunset. 



the morning when the sun rises, and impart to the 

 morning clouds red or crimson colors. 



Fig. 19. 



Let us suppose, as in^. 19, a ray oflight, proceeding from the sun, S, 

 to enter the earth's atmosphere at the point P. The red rays, which 

 compose in part the solar beam, being the least refrangible, or the least 

 deviated from their course, will reach the eye of a spectator at the point 

 A ; while the yellow and blue rays, being refracted to a greater degree, 

 will reach the surface of the earth at the intermediate points B and C. 

 They will, consequently, be quite invisible from the point A. 



550 What, is meant by being " less refrongiblef' 1 



Being less able to be bent. Blue and yellow rays are 

 more easily bent below the horizon through the action 

 of the atmosphere, but red rays are not so much bent 

 down, and therefore we see them later in the evening. 



551 What is the cause of a red sunset f 



The vapor of the air not being actually condensed 

 into clouds, but only on ihe point of being condensed. 



In the same manner, if light be transmitted through steam mingled 

 with air, and therefore on the verge of condensation, it assumes a deep 

 orange or red color. 



552 Why is a red and lowering sky at sunrise an indication of a wet 

 day f 



The red and lowering appearance of the morning sky ? 

 which indicates foul weather, probably depends upon 

 such an excess of vapor being present in the whole 

 atmosphere that clouds are actually forming in the 



