[al:新概念英语（四）] [ar:MP3 同步字幕版（英音）] [ti:Bats] [by:更多学习内容，请到chazidian.com搜索“新概念”] [00:01.47]Lesson 7 [00:03.39]Bats [00:11.30]In what way does echo-location in bats play an utilitarian role? [00:19.78]Not all sounds made by animals serve as language, [00:24.17]and we have only to turn to that extraordinary discovery of echo-location in bats [00:30.34]to see a case in which the voice plays a strictly utilitarian role. [00:36.35]To get a full appreciation of what this means [00:39.73]we must turn first to some recent human inventions. [00:44.50]Everyone knows that if he shouts in the vicinity of a wall or a mountainside, [00:49.97]an echo will come back. [00:52.57]The further off this solid obstruction, [00:55.01]the longer time will elapse for the return of the echo. [00:59.16]A sound made by tapping on the hull of a ship will be reflected from the sea bottom, [01:05.35]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. [01:15.11]So was born the echo-sounding apparatus, now in general use in ships. [01:21.77]Every solid object will reflect a sound, [01:25.65]varying according to the size and nature of the object. [01:30.09]A shoal of fish will do this. [01:32.95]So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish. [01:40.85]With experience, and with improved apparatus, [01:44.48]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. [01:56.28]It has been found that certain bats emit squeaks and by receiving the echoes, [02:02.42]they can locate and steer clear of obstacles -- or locate flying insects on which they feed. [02:09.96]This echo-location in bats is often compared with radar, [02:14.16]the principle of which is similar.