新概念英语85年上外美音版第四册 第9课

（单词翻译）

　　Lesson 9 Curiosities of Animal Life 动物生活趣闻
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 strictly¹ utilitarian² role.
To get a full appreciation³ 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 obstruction⁴ the longer time will elapse for the return of the echo. A sound made by tapping on the hull⁵ of a ship will be reflected from the sea bottom, and by measuring the time interval⁶ 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 apparatus⁷, 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, cod⁸, or other well-known fish, by the pattern of its echo.
A few years ago it was found that certain bats emit squeaks⁹ and by receiving the echoes they could locate and steer¹⁰ clear of obstacles--or locate flying insects on which they feed. This echo-location in bats is often compared with radar¹¹, the principle of which is similar.