Kind words can be short and easy to speak, but their echoes are truly endless.

  
 

MOTHER THERESA (1910-97)

Echoes

Useful Echoes


Dolphin biosonar works with echoing clicks. They can echolocate even in noisy environments, and can do so on near and distant targets simultaneously. They can distinguish between different species of fish (possibly because the swim bladder of each species has a distinctive signature echo). They have a sort of X-ray sonar in that they can detect the internal structure of an object (they can discriminate between two metal discs in which the only difference is the texture of the side that's facing away from them). There is some evidence that they are able to recognise a human fetus inside an expectant mother.
 
Daniel Kish is blind, but has taught himself to navigate using a similar system to dolphins. By making clicks with his tongue and listening for the echoes, he is able to enjoy hiking and mountain biking. The echoes from his clicks can tell him about an object's distance, size, texture and density so much so that he can tell the difference between a metal fence and a wooden fence.

 

Extremely sensitive hearing is called ‘hyperacusis’. Sufferers can find normal levels of sound intolerably loud.

CARL SANDBURG (1878-1967)

Poetry is an echo, asking a shadow to dance.

Ducks’ Quacks


Internet-lore notwithstanding, there is nothing special about a duck’s quack to stop it from echoing. This was proved at the University of Salford by placing a duck in a reverberation chamber. It is possible that this much-repeated myth originated because ducks don’t make loud noises so the echo is often too quiet to be heard.

The huge nose of the proboscis monkey acts as an echo-chamber to amplify its call.

‘Catacoustics’ is the study of echoes.

OLIVER WENDELL HOLMES (1809-94)

The sound of a kiss is not so loud as that of a cannon, but its echo lasts a great deal longer.