400 COLOUR. 



A. They are refracted below the 

 horizon, and are soon made invisible by 

 the curve of the earth. (See last figure.) 



Q. Why are the EDGES of CLOUDS more 

 LUMINOUS than their CENTRES ? 



A. Because the body of vapour is 

 thinnest at the edges of the clouds. 



Q. What is the cause of morning and evening 

 TWILIGHT? 



A. When the sun is below the 

 horizon, the rays (which strike upon the 

 atmosphere or clouds) are bent down 

 towards the earth, and produce a little 

 light called twilight. 



See figure on p. 399. Here the rays of PA will give 

 some light. 



Q. WHY is a ray of LIGHT composed of 



VARIOUS COLOURS ? 



A. If solar light were of one colour 

 only, all objects would appear of that one 

 colour (or else black.) 



Q. Why are some things of ONE COLOTJK, and 

 some of ANOTHER ? 



A. As every ray of light is composed 

 of all the colours of the rainbow, some 

 things reflect one of these colours, and 

 some another. 



