CHAPTER XXVII 

 LIGHT 



187. Diffused Light. From our observations and 

 experiences with light and shadow we know that light 

 travels in straight lines, except when it is reflected by an 

 object or refracted by passing into or out of a transparent 

 substance at an oblique angle. When light falls on rough 

 surfaces like those of trees, fences, roads, etc., it is re- 

 flected in all directions. If light falls on smooth water or 

 on a mirror it is not diffused, but all the light is reflected 

 in such a way that we see an image of the object from 

 which the light is coming. 



Our living rooms would be very imperfectly lighted 

 if it were not for the reflection of diffused light through 

 the windows by the objects outside and if the walls of 

 the rooms did not reflect the light. Reflection of light 

 prevents the shade of trees and houses from being very 

 dark. On cloudy days the light of the sun is reflected 

 from one drop of water to another in the cloud until it 

 finds its way to the earth. The thicker the cloud the 

 less light can get through, and at times the clouds are 

 so dense that artificial lights have to be used to enable 

 us to see. The air is full of very small dust particles. 

 The light reflected back and forth from these par- 

 ticles of dust helps to give the sky a blue color on clear 

 days. Fine water particles like mist give the sky a gray- 

 ish color, 



