新概念第四冊課文精講 Lesson7:蝙蝠
課文7 蝙蝠
104. Not all sounds made by animals serve as language,
動物發(fā)出的聲音不都是用作語言交際。
105. 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.
我們只要看一看蝙蝠回聲定位這一極不尋常的發(fā)現(xiàn)，就可以探究一下聲音在什么情況下有絕對的實用價值。
106. To get a full appreciation of what this means we must turn first to some recent human inventions.
要透徹理解這句話的意義，我們應(yīng)先回顧一下人類最近的幾項發(fā)明。
107. Everyone knows that if he shouts in the vicinity of a wall or a mountainside, an echo will come back.
大家都知道，在墻壁或山腰附近發(fā)出的喊聲，就會聽到回聲。
108. The further off this solid obstruction, the longer time will elapse for the return of the echo.
固體障礙物越遠?；芈暦祷厮脮r間就越長。
109. A sound made by tapping on the hull of a ship will be reflected from the sea bottom,
通過敲擊空船發(fā)出的聲音將會從海底反射回來。
110. 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.
測出回聲間隔的時間，便可算出該處海洋的深度。
111. So was born the echo-sounding apparatus, now in general use in ships.
這樣就產(chǎn)生了目前各種船舶上普遍應(yīng)用的回聲探測儀。
112. Every solid object will reflect a sound, varying according to the size and nature of the object.
任何固體者反射聲音，反射的聲音因物體的大小和性質(zhì)的不同而不同。
113. A shoal of fish will do this.
魚群也反射聲音。
114. So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish.
從測定海深到測定魚群，這一進展比較容易。
115. With experience, and with improved apparatus,
根據(jù)經(jīng)驗和改進了的儀器，
116. 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.
不僅能夠確定魚群的位置，而且可以根據(jù)魚群回聲的特點分辨出是鯡魚、鱈魚，這是人們所熟悉的其他魚。
117. It has been found that certain bats emit squeaks and by receiving the echoes,
人們發(fā)現(xiàn)，某些蝙蝠能發(fā)出尖叫聲，并能通過回聲
118. they can locate and steer clear of obstacles -- or locate flying insects on which they feed.
來確定并躲開障礙物，或找到它們賴以為生的昆蟲。
119. This echo-location in bats is often compared with radar, the principle of which is similar.
蝙蝠這種回聲定位常?？膳c雷達相比較，其原理是相似的。
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