REFLECTION OF HEAT AND LIGHT 



63 



objects on the earth reflect both heat and light. In the 

 summer, the walls of the houses and the pavements of the 

 streets sometimes reflect the heat to such an extent that it 

 becomes almost unbearable. In countries where the sun 

 shines brightly nearly all of the time, as in the Desert of 

 Sahara, reflectors have 

 been so arranged as to 

 reflect the heat of the 

 sun on to boilers and to 

 run steam engines. 



The smooth surfaces 

 of houses often reflect 

 so much of the light 

 falling upon them that 

 the glare is thrown into 

 the windows of sur- 

 rounding houses into 

 which the sun itself 

 cannot shine. If one 

 stands in the right posi- 

 tion, the reflection of 

 trees and other objects 



A REFLECTION ENGINE. 



This engine used the rays of the sun in- 

 stead of coal to heat its boiler. 



can be seen in a smooth 

 lake. But the reflec- 

 tion cannot be seen if the position of the spectator is 

 much changed. The reflected ray must therefore main- 

 tain a certain relation to the ray that strikes the surface 

 from the object, 



In Experiment 33, when the pencil was held perpen- 

 dicular to the mirror at the point where the rays touched the 

 mirror, it was seen that both the ray from the window and 

 the reflected ray made about the same angle with it. These 

 two angles are respectively called the angle of incidence and 

 the angle of reflection. By most careful experimentation 



