RADIATION. 195 



Q. Why can persons in the DARK STREET see 

 into a ROOM (lighted by a candle or lamp) ? 



A. The pupil of the eye expands 

 greatly, when persons are in the dark ; 

 and, therefore, when any one in the 

 dark street looks into a light room, his 

 dilated pupil sees every thing distinctly. 



Q. Why does it always FREEZE on the TOP of 



a MOUNTAIN ? 



A. Air is heated by the reflection of 

 the earth, and not by the rays of the 

 sun ; and, as there is no earth round a 

 mountain-top to reflect heat, therefore, 

 it remains intensely cold. 



CHAPTER XVI. 



4. RADIATION. 



Q. What is meant by RADIATION ? 



A. Radiation means the emission of 

 rays : thus the sun radiates both light 

 and heat ; that is, it emits rays of light 

 and heat in all directions. 



s 2 



