2018年6月大学英语六级听力常考时文：The Origin of Refrigerators

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　　1.When did ice come into household use? ...
        　　2.What performed the cooling in fact? ... of the ice.
        　　3.When was the balance of insulation and circulation needed for an
efficient icebox achieved? Near ...
        　　By the mid-nineteenth century，the term “icebox” had entered the American
language， but ice was still only beginning to affect the diet of ordinary
citizens in the United States. The ice trade grew with the growth of cities. Ice
was used in hotels，taverns， and hospitals， and by some forward-looking city
dealers in fresh meat，fresh fish，and butter. After the Civil War，it came into
household use. This had become possible because a new household convenience，the
icebox，a precursor of the modern refrigerator，had been invented. Making an
efficient icebox was not as easy as we might now suppose. In the early
nineteenth century，the knowledge of the physics of heat，which was essential to a
science of refrigeration， was rudimentary. The commonsense notion the best
icebox was one that prevented the ice from melting was of course mistaken，for it
was the melting of the ice that performed the cooling. Nevertheless，early
efforts to economize ice included wrapping up the ice in blankets，which kept the
ice from doing its job. Not until near the end of the nineteenth century did
inventors achieve the delicate balance of insulation and circulation needed for
an efficient icebox. But as early as 1803，Thomas Moore had been on the right
track. He owned a farm about twenty miles outside the city of Washington，for
which the village of Georgetown was the market center. When he used an icebox of
his own design to transport his butter to market，he found his butter，still fresh
and hard in neat，one-pound bricks，was more welcomed.