ECHOES OF BATS AND MEN 



Fig. 11. The frequency and wave length of a bat's 

 sound vary during each chirp. This diagram, which is 

 approximately to scale, illustrates the small amount of 

 sound reflected by one insect. 



United States begin each of their orientation sounds at 

 about 90 kc and end at 45 kc. Since each sound lasts 

 only about 2 milliseconds, this is a very rapid change in 

 frequency; indeed, this bat sweeps through a frequency 

 band double the whole range of the human ear in 2 



86 



