128 



FIRST YEAR SCIENCE 



composed of many different colors. In fact it is the ab- 

 sorption of some of these colors and the reflection of 

 others which make objects appear of 

 different color. 



Light itself is a vibration which has 

 the power of affecting the optic nerve, 

 and the different colors are vibrations 

 of different lengths. Now the sunlight 

 is affected by the air through which it 

 comes. If there is smoke or dust in 

 the air, the sun will appear to be red. 

 When the sun sets at night and the 

 rays come to us through a considerable 

 thickness of air which is near the sur- 

 face of the earth and contains dust, the 

 light often appears red. On the top 

 o'f a high mountain or on a clear day or 

 when the sun is high overhead the sky 

 appears blue. - Both, these- colors are 

 due to the effect of the atmosphere on 

 transmitted light. 



Sometimes after a shower an arch 

 appears in the heavens composed of 

 beautiful colors ; we call this a rain- 

 bow. In this case the sunlight is 

 broken into different colors by the 



Fig. 62. 



drops of water which still fall in the distance, just as it is 

 when passing through a prism. 



Sometimes the sun or moon is surrounded by bright 

 rings called, when of small diameter, coronas, and when of 

 great diameter, halos. These rings are due to the effect 

 of water or ice particles on the light coming frojn the" 

 sun or the moon. 



Under certain conditions it may happen that light com- 



