ECHOES OF BATS AND MEN 



wave lengths of a few centimeters. When such wave 

 lengths strike the wall of a building, they are reflected 

 almost exactly as Hght waves would be from a mirror. If 

 the clicker is pointed directly at the wall, the echo will 

 come straight back, but if the emitted sound strikes ob- 



Zdab= Zeac 



Fig. 9. The law of reflection describes the way in 

 which sound reflects from a large flat surface. When 

 making this experiment, observe the relative positions 

 of the two boys. 



liquely, the echoes will rebound away from the clicker, 

 as indicated in Fig. 9. This is why it is so easy to locate 

 a building by scanning with the clicker; the echo is far 

 louder when the horn is pointed straight at the wall. Two 

 people can co-operate in a simple experiment that dem- 



76 



