动物发出的声音并非全都充当语言，我们只需转而关注蝙蝠回声定位这一非凡发现，便能看到一个声音发挥纯实用性功能的案例。
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.
要充分理解这意味着什么，我们首先必须转向一些近代人类发明。
To get a full appreciation of what this means we must turn first to some recent human inventions.
每个人都知道，如果在墙壁或山坡附近大声喊叫，回声就会传回来。
Everyone knows that if he shouts in the vicinity of a wall or a mountainside, an echo will come back.
这一固体障碍物离得越远，回声返回所需的时间就越长。
The further off this solid obstruction, the longer time will elapse for the return of the echo.
通过敲击船体发出的声音会从海底反射回来，通过测量敲击声与收到回声之间的时间间隔，就能计算出该点的海水深度。
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.
回声测深装置就这样诞生了，如今在船舶中已被普遍使用。
So was born the echo-sounding apparatus, now in general use in ships.
每一个固体物体都会反射声音，反射的情况因物体的大小和性质不同而有所差异。
Every solid object will reflect a sound, varying according to the size and nature of the object.
一群鱼也会做到这一点（即反射声音）。
A shoal of fish will do this.
因此，从定位海底到定位鱼群，不过是相对简单的一步。
So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish.
凭借经验，加上改进后的仪器设备，现在不仅可以定位鱼群，还能通过回声的特征判断其是鲱鱼、鳕鱼，还是其他常见鱼类。
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.
人们发现，某些蝙蝠会发出尖叫声，通过接收回声，它们能够定位并避开障碍物——或者定位它们赖以为食的飞行昆虫。
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.
蝙蝠的这种回声定位常常与雷达相比较，两者的原理是相似的。
This echo-location in bats is often compared with radar, the principle of which is similar.