新概念英語第四冊
Lesson 7 Bats
1 . 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，我們應先回顧一下人類最近的幾項發明。
2 . Not all sounds made by animals serve as language.動物發出的聲音不都是用作語言交際。
3 . A shoal of fish will do this.魚群也反射聲音。
4 . 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。
5 . 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的不同而不同。
6 . they can locate and steer clear of obstacles -- or locate flying insects on which they feed.並能通過回聲來確定並躲開障礙物，或找到它們賴以為生的昆蟲。
7 . 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。
8 . With experience, and with improved apparatus,根據經驗和改進了的儀器，
9 . 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常可與雷達相比較，其原理是相似的。
10 . So was born the echo-sounding apparatus, now in general use in ships.這樣就產生了目前各種船舶上普遍應用的回聲探測儀。
11 . The further off this solid obstruction, the longer time will elapse for the return of the echo.固體障礙物越遠。回聲返回所用時間就越長。
12 . It has been found that certain bats emit squeaks and by receiving the echoes,人們發現，某些蝙蝠能發出尖叫聲，
13 . 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，在牆壁或山腰附近發出的喊聲，就會聽到回聲。
14 . 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現，就可以探究一下聲音在什麼情況下有絕對的實用價值。
15 . 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。
16 . A sound made by tapping on the hull of a ship will be reflected from the sea bottom,敲打船體所發了的聲音會從海底傳回來，