SONAR AND RADAR 



duty cycle would be about 0.0007. This means that if 

 we were to use average power rather than peak power 

 in our comparison, the bats would suffer by a factor 

 of about 100. Yet a partisan of the bats might offer in 

 rebuttal the consideration that we allowed 10 per cent of 

 the animal's weight for its sonar apparatus, whereas the 

 weight of the radar set was a much smaller fraction of 

 the mass of the airplane that carried it. From the bat's 

 point of view it would perhaps be more valid to compare 

 its whole weight with that of the entire airplane. 



If we take the broadest view, it is obvious that bats 

 and other Uving animals are vastly more efficient than 

 radars and airplanes, even though it is difficult to attach 

 numbers to the comparison. Bats maintain and repair 

 their Uving machinery; airplanes and radar sets must be 

 manufactured and repaired by men. Bats catch and di- 

 gest all the food that provides power for their bodily 

 mechanisms; airplanes are not expected to refuel by 

 catching birds, and the fuel pumped to them requires no 

 chemical processing in the plane before use. Nor do any 

 artifical mechanisms reproduce themselves. The unusual 

 aspect of the comparison we have been making is that a 

 Hving mechanism can be compared directly with a radar 

 set on almost the same terms that an engineer would 

 employ in comparing one radar with another. The re- 

 sults of the comparison inspire a healthy respect for the 

 mechanisms of flesh and blood which have evolved in 

 nature under the pressure of natural selection. 



127 



