122 FIRST YEAR COURSE IN GENERAL SCIENCE 



glass without warming it; but if sunlight falls on an opaque 

 surface, part of the light is absorbed and changed into heat. 



133. Reflection. No one expects to see around a corner 

 any more than through a wall. The reason why one cannot 

 do this is because light travels in straight lines. This is true 

 of reflected light as well as of light coming directly from its 

 source. A polished surface of metal or glass makes the best 

 reflector of light, but all surfaces reflect a part of the light 

 which falls upon them. It is by this reflection of light that 

 we see bodies that are not themselves luminous. 



Vision is partly a process of the mind. We are accustomed 

 to the fact that objects are visible by means of light passing 



FIG. 57. A MIRROR 



1. Explain how a person, by aid of a mirror, can know what is at one 

 side or back of him. 2. Why does a kitten placed before a mirror try to 

 look behind it? 3. Explain the use made of a mirror in the front of a motor 

 vehicle. 



in straight lines to the eye. Therefore we mentally follow 

 the lines back to the place from which they seemed to start. 

 The reflection seen in the mirror seems to come from 

 an object at the mirror or behind it, because the light 

 comes to us from that direction. A mirror is usually so 

 placed that objects behind or at one side of the observer 

 can be seen while he is looking straight ahead. Careful 

 arrangements of mirrors may reflect images of images of 

 objects. One object may have several images if the mir- 

 rors are placed parallel, or at an angle to each other. Some 



