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Lesson 7 |
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Bats |
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In what way does echo-location in bats play an utilitarian role? |
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and we have only to turn to that extraordinary discovery of echo-location in bats |
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to see a case in which the voice plays a strictly utilitarian role. |
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To get a full appreciation of what this means |
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we must turn first to some recent human inventions. |
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Everyone knows that if he shouts in the vicinity of a wall or a mountainside, |
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an echo will come back. |
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The further off this solid obstruction, |
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the longer time will elapse for the return of the echo. |
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and by measuring the time interval between the taps and the receipt of the echoes the depth of the sea at that point can be calculated. |
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So was born the echo-sounding apparatus, now in general use in ships. |
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Every solid object will reflect a sound, |
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varying according to the size and nature of the object. |
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A shoal of fish will do this. |
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So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish. |
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With experience, and with improved apparatus, |
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it is now possible not only to locate a shoal but to tell if it is herring, cod, or other well-known fish, by the pattern of its echo. |
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It has been found that certain bats emit squeaks and by receiving the echoes, |
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they can locate and steer clear of obstacles -- or locate flying insects on which they feed. |
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This echo-location in bats is often compared with radar, |
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the principle of which is similar. |
