Lesson 7 Bats_中国英语学习网

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Lesson 7 Bats

中国英语学习网　　　更新时间：2007-02-28

Not all sounds made by animals serve as language, and we have only to turn to
that extraordinary discovery of echo-location in bats to see a case in which the
voice plays a strictly utilitarian role.
To get a full appreciation of what this means we must turn first to some recent
human inventions. Everyone knows that if he shouts in the vicinity of a wall or
a mountainside, an echo will come back. The further off this solid obstruction
the longer time will elapse for the return of the echo. A sound made by tapping
on the hull of a ship will be reflected from the sea bottom, 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. So was born the echo-sounding apparatus,
now in general use in ships. Every solid object will reflect a sound, varying according
to the size and nature of the object. A shoal of fish will do this. So it is a
comparatively simple step from locating the sea bottom to locating a shoal of
fish. With experience, and with improved apparatus, 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.
A few years ago it was found that certain bats emit squeaks and by receiving
the echoes they could locate and steer clear of obstacles--or locate flying insects
on which they feed. This echo-location in bats is often compared with radar, the
principle of which is similar.

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　听力新概念英语第四册 NCE 4相关听力

·	Lesson 1 Finding Fossil man	·	Lesson 2 Spare that spider	·	Lesson 3 Matterhorn man
·	Lesson 4 Seeing hands	·	Lesson 5 Youth	·	Lesson 6 The sporting spirit
·	Lesson 7 Bats	·	Lesson 8 Trading standards	·	Lesson 9 Royal espionage
·	*Lesson 10 Silicon valley	·	Lesson 11 How to grow old	·	Lesson 12 Banks and their customers
·	Lesson 13 The search for oil	·	Lesson 14 The Butterfly Effect	·	Lesson 15 Secrecy in industry
·	Lesson 16 The modern city	·	Lesson 17 A man-made disease	·	Lesson 18 Porpoises
·	Lesson 19 The stuff of dreams	·	Lesson 20 Snake poison	·	Lesson 21 William S. Hart and the ea
·	Lesson 22 Knowledge and progress	·	Lesson 23 Bird flight	·	Lesson 24 Beauty
·	Lesson 25 Non-auditory effects of no	·	Lesson 26 The past life of the earth	·	Lesson 27 The ‘Vasa’
·	Lesson 28 Patients and doctors	·	Lesson 29 The hovercraft	·	Lesson 30 Exploring the sea-floor
·	Lesson 31 The sculptor speaks	·	Lesson 32 Galileo reborn	·	Lesson 33 Education
·	Lesson 34 Adolescence	·	Lesson 35 Space odyssey	·	Lesson 36 The cost of government

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