第 7 课 · Bats

Bats

蝙蝠

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.

动物发出的声音并非全都用作语言；我们只要看看蝙蝠回声定位这一非凡发现，就能看到一个声音严格只起实用作用的例子。

To get a full appreciation of what this means we must turn first to some recent human inventions.

要充分理解这意味着什么，我们必须先来看看人类近期的一些发明。

Everyone knows that if he shouts in the vicinity of a wall or a mountainside, an echo will come back.

人人都知道，如果在墙壁附近或山腰上大喊一声，就会有回声传回来。

The further off this solid obstruction, the longer time will elapse for the return of the echo.

这一实心障碍物离得越远，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.

在船体上敲击发出的声音会从海底反射回来；通过测量敲击与接收到回声之间的时间间隔，就能算出该处海的深度。

So was born the echo-sounding apparatus, now in general use in ships.

回声测深仪就这样诞生了，如今在船舶上得到普遍使用。

Every solid object will reflect a sound, varying according to the size and nature of the object.

每一个固体都会反射声音，反射的情况随物体的大小和性质而有所不同。

A shoal of fish will do this.

鱼群也会这样反射声音。

So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish.

因此，从测定海底位置到发现鱼群，只是相对简单的一步。

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.

有了经验和改进的仪器，如今人们不仅能确定鱼群的位置，还能根据回声的样式判断那是鲱鱼、鳕鱼还是其他人们熟知的鱼类。

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，某些蝙蝠会发出短促的尖叫；通过接收回声，它们能确定障碍物的位置并加以避开——或者找到它们捕食的飞虫。

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被拿来与雷达相比，两者的原理是相似的。