TWILIGHT 103 



from the sky in this manner of diffused reflection. Since the 

 reflecting surface is so large, there are no definite shadows pro- 

 duced, the light fading away gradually on all sides of an object. 

 The best light for the eyes is diffused light. Experiment 35 

 showed diffusion of light by means of the suspended particles 

 in the water. 

 References : 



1. 1304:233. Diffraction of Light. 



2. 1803 : 396-397. Diffusion of Light. 



a. 1801 : 197-198. Diffused Reflection. 



b. 1802 : 214. Irregular Reflection Diffusion. 



c. 1804 : 333-335. Diffused Light. 



d. 1805 : 225. Diffusion of Light. 



e. 1807 : 269-270. Diffusion of Light. 

 /. 1809 : 284r-285. Diffused Light. 



g. 1810 : 337-338. Regular and Irregular Reflection. 

 h. 1811 : 222. Diffused Reflection of Light. 



75. TWILIGHT 



After the sun sets, darkness does not begin immediately. 

 In fact, the western sky becomes brighter a little while after 

 the sun has set than it was just at sunset. This is called the 

 afterglow, and is due to the reflection of light from particles 

 in the higher air. In a very dry, clear atmosphere the after- 

 glow is not so marked as it is in a locality where there 'is more 

 water and dust held in suspension in the atmosphere. This 

 dust is not to be confused with the dust of the earth as we find 

 it in streets, for it is very fine and practically invisible. 



Twilight means two lights, the sun and the stars, and 

 lasts usually until the sun is 18 below the horizon. 

 References : 



1. 1002 : 138. Twilight Due to the Atmosphere. 



2. 1103:24-25. Length of Twilight. 



