LIGHT AND COLOUR 



case of light, the difference in the length of the 

 waves, or more truly the difference in the rate 

 at which they vibrate, causes the difference in 

 colour red light consists of longer waves, blue 

 light of shorter ones. Although waves of all 

 lengths seem to travel at the same rate through 

 the free ether of space, when they enter glass or 

 water their speed is reduced by different amounts, 

 the blue waves are kept back more than the red 

 ones. They are thus separated from each other, 

 and the different colours may come out of the 

 glass or water in different directions, showing us 

 the colours of the rainbow. 



As we found out, leaves, flowers, animals, 

 and other natural objects seem to choose out 

 certain of these waves more freely than others, 

 to such an extent that the light which comes 

 back from them has been deprived of some of 

 its parts. We may well ask what becomes of 

 these absorbed waves ? Now we know that a 

 body placed in the sun's rays gets hot, and if we 

 are observant we ought to know that a black 

 body gets hotter than a white one. At any rate, 

 we all put on white dresses and light clothes in 

 summer-time, which shows that we act on this 

 principle even if we have never troubled to 

 think about it. But we now understand that a 

 white body is one that sends back all the parts 

 of the white light, while the black body takes 

 them all in. We gather from this, then, that the 

 rays which are absorbed are turned somehow 



(59) 



