ECHO-LOCATION 183 



for millions of years by several sorts of animals. In these 

 animals, too, it had been brought to a pitch of perfection 

 that man has not yet been able to imitate, and in them the 

 apparatus is packed into a space so small that his electronic 

 instruments appear absurdly cumbersome in comparison. 

 Furthermore it is rather surprising that until man made his 

 inventions he had barely an inkling of the existence of echo- 

 location in the animals, whereas if he had discovered what 

 the animals were doing he might have made his inventions 

 nmch sooner, though it would have been difficult for him to 

 develop them for practical use until technology had provided 

 him with the means. 



The animals that we know make use of echo-location are 

 the bats, the whales and dolphins, and some of the birds — 

 there may of course be many others in which it is awaiting 

 discovery. The way of life of all these animals is such that 

 they are active at times or in places where the sense of sight 

 is diminished or impaired ; the bats fly and hunt by night, 

 the whales and dolphins live in the sea where even in clear 

 water the brightness of the light rapidly diminishes with 

 depth below the surface, and in turbid water is often ex- 

 tinguished at very moderate depths, and the birds that use 

 echo-location build their nests in the darkness of extensive 

 caves. These animals are able, without seeing, to find their 

 way about, to avoid obstacles, and some of them at least to 

 catch their prey. They not only locate the objects in their 

 surroundings and know their distance and direction, but get 

 information about their size, shape and, doubtless, many 

 other details. 



Soon after man's invention of radio-location was brought 

 inco practical use it was given the convenient made-up name 

 of "radar", and when the analogous use of sound echo- 

 location by animals was discovered it was no more than 

 natural that it should be called "sonar" — a name which is 

 now in universal use. The essence of sonar is generally the 

 giving out of very short, abrupt bursts of sound which can 

 bounce back as echoes, although it is now known that there 

 is also another way by which location can be achieved. In 

 the first method, throwing out short bursts of sound and 

 catching them on their return can be compared to throwing 



