ECHOES OF BATS AND MEN 



clusively for underwater echolocation, while radar is 

 used only in air or outer space. 



Echoes under Water 



The tragic sinking of the Titanic by an iceberg in 1912 

 prompted the first of many efforts to invent a means of 

 detecting icebergs in darkness or in fog. Even in 1959, 

 icebergs caused the sinking of an ocean liner fully 

 equipped with modem aids to navigation. Sir Hiram 

 Maxim, a prolific inventor who in the late nineteenth 

 century attempted to build flying machines, proposed 

 that bats' methods of navigation be copied directly in 

 the design of safety devices for ocean-going ships. Un- 

 fortunately, however, he did not really know how bats 

 navigate— for the simple reason that the subject had been 

 largely neglected since the days of Spallanzani. He sur- 

 mised correctly that bats used echolocation but was in- 

 correct when he assumed that the probing sound came 

 from the beating of their wings. Hence he advised that 

 ships generate very /ow-frequency sounds of roughly 15 

 c.p.s. and that receiving devices for such frequencies be 

 mounted on the bow of the ship. Faint echoes from this 

 sound were to ring a small bell, loud ones a large gong, 

 so that the crew could judge the seriousness of the 

 danger. 



Maxim's idea was, nevertheless, a step forward in 

 understanding bat navigation, for it introduced for the 

 first time the idea that sounds inaudible to human ears 

 might be the basis of bats' uncanny abihty to fly in dark- 

 ness. But his ideas did not lead to any practical method 

 for detecting icebergs, and for at least two important 

 reasons. In the first place, the low frequencies which 

 he proposed meant that long wave lengths would have 

 been involved; 15-c.p.s. sound has a 20-meter wave. It 



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