407.lrc

[00:00.000]--- lesson 7  Bats 蝙蝠
[00:03.579]Not all sounds made by animals serve as language,^动物发出的声音不都是用作语言交际。
[00:07.889]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.^我们只要看一看蝙蝠回声定位这一极不寻常的发现，就可以探究一下声音在什么情况下有绝对的实用价值。
[00:19.618]To get a full appreciation of what this means we must turn first to some recent human inventions.^要透彻理解这句话的意义，我们应先回顾一下人类最近的几项发明。
[00:27.298]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，在墙壁或山腰附近发出喊声，就会听到回声。
[00:35.109]The further off this solid obstruction, the longer time will elapse for the return of the echo.^固体障碍物越远。回声返回所用时间就越长。
[00:41.300]A sound made by tapping on the hull of a ship will be reflected from the sea bottom,^敲打船体所发出的声音会从海底传回来。
[00:47.464]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.^测出回声间隔的时间，便可算出该处海洋的深度。
[00:56.895]So was born the echo-sounding apparatus, now in general use in ships.^这样就产生了目前各种船舶上普遍应用的回声探测仪。
[01:03.451]Every solid object will reflect a sound, varying according to the size and nature of the object.^任何固体都反射声音，反射的声音因物体的大小和性质的不同而不同。
[01:11.262]A shoal of fish will do this.^鱼群也反射声音。
[01:13.770]So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish.^从测定海深到测定鱼群，这一进展比较容易。
[01:21.345]With experience, and with improved apparatus,^根据经验和改进了的仪器，
[01:25.029]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.^不仅能够确定鱼群的位置，而且可以根据鱼群回声的特点分辨出是鲱鱼、鳕鱼，还是人们所熟悉的其他鱼。
[01:36.131]It has been found that certain bats emit squeaks and by receiving the echoes,^人们发现，某些蝙蝠能发出尖叫声，并能通过回声
[01:42.583]they can locate and steer clear of obstacles -- or locate flying insects on which they feed.^来确定并躲开障碍物，或找到它们赖以为生的昆虫。
[01:49.584]This echo-location in bats is often compared with radar, the principle of which is similar.^蝙蝠的这种回声定位常常可与雷达相比较，其原理是相似的。