Lesson 7

Bats

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.
并非所有由动物制造的声音都充当语言，我们只需看看蝙蝠回声定位这一非凡发现，就能看到一个声音仅起严格功利性作用的案例。
To get a full appreciation of what this means we must turn first to some recent human inventions.
为了充分理解这意味着什么，我们必须首先转向一些最近的人类发明。
Everyone knows that if he shouts in the vicinity of a wall or a mountainside, an echo will come back.
每个人都知道，如果他在墙或山坡附近大喊，回声就会回来。
The further off this solid obstruction, the longer time will elapse for the return of the echo.
距离这个坚固的障碍物越远，回声返回所需的时间就越长。
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.
通过敲击船体产生的声音会被海底反射，通过测量敲击与接收回声之间的时间间隔，可以计算出该点的海深。
So was born the echo-sounding apparatus, now in general use in ships.
因此回声探测设备诞生了，现在在船只中普遍使用。
Every solid object will reflect a sound, varying according to the size and nature of the object.
每一个固体物体都会反射声音，并根据物体的大小和性质而变化。
A shoal of fish will do this.
一群鱼将会这样做。
So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish.
因此，从定位海底到定位鱼群，这是一个相对简单的步骤。
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.
凭借经验和改进的设备，现在不仅可以定位鱼群，还可以通过回声模式分辨出它是鲱鱼、鳕鱼还是其他众所周知的鱼类。
It has been found that certain bats emit squeaks and by receiving the echoes, they can locate and steer clear of obstacles—or locate flying insects on which they feed.
人们发现，某些蝙蝠通过发出尖叫声并接收回声，能够定位并避开障碍物，或者定位它们赖以觅食的飞行昆虫。
This echo-location in bats is often compared with radar, the principle of which is similar.
蝙蝠中的这种回声定位经常被与雷达相比较，其原理是相似的。