万物简史 第365期:进入对流层(6)

People who habitually¹ live at altitude have often spent thousands of years developing disproportionately large chests and lungs, increasing their density² of oxygen-bearing red blood cells by almost a third, though there are limits to how much thickening with red cells the blood supply can stand. Moreover, above 5,500 meters even the most well-adapted women cannot provide a growing fetus³ with enough oxygen to bring it to its full term.

生活在高处的人往往要经过几千年才渐渐拥有特别大的胸腔和肺部，使携带氧气的红细胞浓度增加差不多三分之一。可是，血浓所能承受的红细腹浓度是有限度的，要是浓度太大，血液流动就无法顺畅。而且，在5500米以上的高度，连已经完全适应的妇女也无法为发育中的胎儿提供足够的氧气，不到足月就会把他（她）生下来。

In the 1780s when people began to make experimental balloon ascents⁴ in Europe, something that surprised them was how chilly⁵ it got as they rose. The temperature drops about 3 degrees Fahrenheit⁶ with every thousand feet you climb. Logic⁷ would seem to indicate that the closer you get to a source of heat, the warmer you would feel. Part of the explanation is that you are not really getting nearer the Sun in any meaningful sense. The Sun is ninety-three million miles away. To move a couple of thousand feet closer to it is like taking one step closer to a bushfire in Australia when you are standing⁸ in Ohio, and expecting to smell smoke. The answer again takes us back to the question of the density of molecules⁹ in the atmosphere. Sunlight energizes¹⁰ atoms. It increases the rate at which they jiggle and jounce, and in their enlivened state they crash into one another, releasing heat. When you feel the sun warm on your back on a summer's day, it's really excited atoms you feel. The higher you climb, the fewer molecules there are, and so the fewer collisions between them.

18世纪80年代，欧洲有人开始乘气球做攀升试验。他们吃惊地发现，他们升得越高，上面的温度越低。每爬高1000米，温度下降大约1.6摄氏度。从逻辑上说，离热热源越近，似乎应当越觉得暖和。部分解释是，你其实并没有接近太阳多少。太阳在1.5亿公里以外。朝它移近几百米，就如站在俄亥俄州，朝澳大利亚的丛林大火走近一步，指望闻到烟味。若要回答这个问题，我们又得回到大气里分子密度的问题。阳光激活原子，它增加了原子的运动速度；原子在激活的状态之下互相撞击，释放热量。夏日里背上感到太阳是暖烘烘的，你感到的其实是阳光在激活原子。你爬得越高，那里的原子越少，因此它们的撞击次数就越少。

1 habitually   

ad.习惯地，通常地

参考例句：

• The pain of the disease caused him habitually to furrow his brow. 病痛使他习惯性地紧皱眉头。
• Habitually obedient to John, I came up to his chair. 我已经习惯于服从约翰，我来到他的椅子跟前。

2 density   

n.密集，密度，浓度

参考例句：

• The population density of that country is 685 per square mile.那个国家的人口密度为每平方英里685人。
• The region has a very high population density.该地区的人口密度很高。

3 fetus   

n.胎，胎儿

参考例句：

• In the fetus,blood cells are formed in different sites at different ages.胎儿的血细胞在不同时期生成在不同的部位。
• No one knows why a fetus is not automatically rejected by the mother's immune system. 没有人知道为什么母亲的免疫系统不会自动排斥胎儿。

4 ascents   

n.上升( ascent的名词复数 )；（身份、地位等的）提高；上坡路；攀登

参考例句：

• The cart was very heavy, and in addition, there were many ascents. 这辆车实在难拉，而且又很重，还得上许多坡。 来自互联网
• Balloon ascents overcome this hazard with ease. 升空的气球能轻而易举地克服这一困难。 来自互联网

5 chilly   

adj.凉快的，寒冷的

参考例句：

• I feel chilly without a coat.我由于没有穿大衣而感到凉飕飕的。
• I grew chilly when the fire went out.炉火熄灭后，寒气逼人。

6 Fahrenheit   

n./adj.华氏温度；华氏温度计(的)

参考例句：

• He was asked for the boiling point of water in Fahrenheit.他被问到水的沸点是华氏多少度。
• The thermometer reads 80 degrees Fahrenheit.寒暑表指出华氏80度。

7 logic   

n.逻辑(学)；逻辑性

参考例句：

• What sort of logic is that?这是什么逻辑？
• I don't follow the logic of your argument.我不明白你的论点逻辑性何在。

8 standing   

n.持续，地位；adj.永久的，不动的，直立的，不流动的

参考例句：

• After the earthquake only a few houses were left standing.地震过后只有几幢房屋还立着。
• They're standing out against any change in the law.他们坚决反对对法律做任何修改。

9 molecules   

分子( molecule的名词复数 )

参考例句：

• The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。
• Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。

10 energizes   

v.给予…精力，能量( energize的第三人称单数 )；使通电

参考例句：

• However, heating energizes the vibrational, rotational, and electronic motions all at once. 但是，加热会一下子把振动、转动和电子运动统统加强。 来自英汉非文学 - 科技
• Purpose always produces passion. Nothing energizes like a clear purpose. 目的往往会带来热忱，没有任何东西比清晰的目的更有动力。 来自互联网