7-6. So was born the echo-sounding apparatus, now in general use in ships.

【译文】目前船舶上普遍应用的回声探测仪就是这样产生的。

【讲解】该句是倒装句。自然语序是The echo-sounding apparatus, now in general use in ships, was so born.这里用倒装句是为了强调，也是因为主语太长。now in general use in ships作apparatus的非限制性定语。另请注意，句首的so不是连词，所以不能译为“于是”、“因此”，它仍是副词，作in this way解。这是个倒装句，如果so是连词，作therefore解，那就不可能是倒装句，全句要变为So the echo-sounding apparatus, now in general use in ships, was born。

【单词和短语】

apparatus：器械；器具；仪器；装置（the set of tools and machines that you use for a particular scientific, medical, or technical purpose），

例如：
medical apparatus 医疗器械

7-7. Every solid object will reflect a sound, varying according to the size and nature of the object.

【译文】凡是固体都反射声音，反射的声音因物体体积和质地各异而有所区别。

【讲解】varying according to the size and nature of the object作方式状语，修饰reflect。

7-8. A shoal of fish will do this.

【译文】鱼群亦会反射声音。

【单词和短语】

a shoal of fish亦可用a school of fish表达。

7-9. So it is a comparatively simple step from locating the sea bottom to locating a shoal of fish.

【译文】因此，从测定海底深度到测定鱼群的位置这一进展相对较易。

7-10. 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.

【译文】根据经验和改进了的仪器，人们不仅能确定鱼群的位置，还可以根据鱼群回声的特点辨别鲱鱼、鳕鱼还是其他人们熟知的鱼种。

【讲解】it is now possible…its echo中it是形式主语，not only to locate a shoal but…well-known fish是真正的主语。其中两个动词不定式短语由连词not only…but…连接。if it is herring, cod, or other well-known fish作tell的宾语从句，if意为“是否”。by the pattern of its echo作方式状语，修饰locate和tell。herring和cod后的逗号用以分隔句中的并列成分。

7-11. 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.

【译文】人们已发现，某些蝙蝠能发出尖叫并通过回声确定并躲开障碍物，或找到它们赖以为生的昆虫。

【讲解】obstacle作locate和steer clear of的宾语。obstacles后的破折号引出被强调的词语。they feed指bats feed。

【单词和短语】

steer clear (of someone/something)：绕开，避开（to avoid sb. or sth. unpleasant or difficult），

例如：
She steered clear of being associated with such people.
她避免与这种人交往。

feed on：以……为食物，吃，食（if an animal feeds on a particular food, it usually eats that food），

例如：
Sheep feed mostly on grass. 羊主要以草食。

Owls feed on mice and other small animals.
猫头鹰以老鼠和其他小动物为食。

7-12. This echo-location in bats is often compared with radar, the principle of which is similar.

【译文】蝙蝠这种回声定位常与雷达相比较，二者原理相似。

【讲解】the principle of which is similar是非限制性定语从句。which代表radar。