part 10

90 The body has many different ways of keeping itself warm enough and not too warm. It uses up more food, more fuel for the cells, in cold weather. It shivers—that is, its muscles go on making quick little motions to keep it warm. We cannot stop ourselves from shivering. The body's heating system is not under our conscious control; it is automatic. To stop shivering we have to warm ourselves some other way: we may run or walk quickly, or take hot drinks, or cover ourselves up warmly, or use hot water bottles to warm our beds.

身体有许多不同的方法来保持足够的温暖和不太温暖。 在寒冷的天气里，它会消耗更多的食物，更多的细胞燃料。 它会颤抖——也就是说，它的肌肉会继续做一些快速的小动作来保暖。 我们无法阻止自己颤抖。 身体的加热系统不受我们意识的控制；这是自动的。 为了停止颤抖，我们必须用其他方式来温暖自己：我们可能会跑或走得很快，或者喝热饮，或者把自己盖得很暖和，或者用热水瓶来温暖我们的床。

91 Our bodies give off some of their heat all the time by sending a little liquid out through the skin. Sometimes the amount gets greater and our skin becomes wet. This cools the body quickly. Here the man on the left is shivering because he has been waiting in line for a long time in the cold wind. The man on the right is wet all over because he got too hot in the sun. He is drinking water because he feels the need of it. He is thirsty.

我们的身体一直通过皮肤散发出一些液体来散发热量。 有时量会变大，我们的皮肤就会变湿。 这能迅速冷却身体。 图中左边的人因为在寒风中排了很长时间的队而发抖。 右边的人全身湿透了，因为他在太阳下太热了。 他正在喝水，因为他觉得需要喝水。 他渴了。

92 This man is in training. He is going to run a distance of one mile in the shortest possible time. The fastest runners before him have taken a little under four minutes and he wants to make a new record. When a man runs a mile in four minutes he is going at a rate of fifteen miles an hour, but it is not possible to keep running at this rate very long. The runner is standing now in front of his doctor who has an instrument in his hand. Through this the doctor can hear the sounds made by the runner's heart.

这个人正在接受训练。 他要在尽可能短的时间内跑完一英里的距离。 在他之前跑得最快的人用时不到4分钟，他想创造一项新纪录。 当一个人在四分钟内跑完一英里时，他的速度是每小时15英里，但以这种速度跑很长时间是不可能的。 跑步者现在站在他的医生面前，医生手里拿着一个仪器。 通过这个，医生可以听到跑步者的心脏发出的声音。

93 Now the doctor is taking the man's pulse. He has his finger on the man's wrist and is counting the times his heart pumps the blood in one minute. The doctor can feel the motion or pulsing of the blood every time the man's heart pumps. In most people the pulse rate is between seventy and eighty times a minute. In children it is higher. The runner's pulse rate is 72. It will be higher when he is running.

现在医生正在给那人把脉。 他把手指放在那个人的手腕上，数着他的心脏在一分钟内泵血的次数。 每次病人心脏跳动时，医生都能感觉到血液的运动或脉搏。 大多数人的脉搏在每分钟70到80次之间。 儿童的比例更高。跑步者的脉搏率是72。 当他跑步时，它会更高。

94 There is a good story about the use the great Italian scientist Galileo once made of his knowledge of the pulse rate. Galileo lived three hundred years ago before people had watches for measuring time. In the sixteenth century there were very few clocks in the world and no watches. One day when Galileo was a young man of eighteen, he was in the great church of the city of Pisa where he lived. Watching the motion of a light hanging down on a long chain from the roof high above his head, he saw that as the light moved forward and back on its chain, it seemed to take the same time between turns, however far it went.

有一个很好的故事是关于伟大的意大利科学家伽利略如何运用他对脉搏率的知识的。 伽利略生活在300年前，那时人们还没有用来测量时间的手表。 在16世纪，世界上钟表很少，也没有手表。 当伽利略还是一个18岁的年轻人的时候，有一天，他在他居住的比萨城的大教堂里。 他注视着从他头顶高处的屋顶上垂下来的一根长链子上的一盏灯的运动，他看到，当这盏灯在链子上前后移动时，不管它走多远，似乎两次转弯所用的时间都是一样的。

95 To see if he was right about the motion of the light, Galileo put his fingers on his wrist. He timed the motion of the light as it went forward and back on its chain, measuring it by his pulse rate. He was right. He had the proof. He could prove that the time was the same, however short or long the journey of the light through the air was. Galileo had made a great discovery about the motion of a pendulum. Among other things this discovery made possible a better instrument for measuring time—the pendulum clock.

为了验证他关于光的运动是否正确，伽利略把他的手指放在手腕上。 他通过自己的脉搏率来测量光线在链条上来回移动的时间。 他是对的。他有证据。 他可以证明，无论光在空气中传播的路程是长是短，时间都是一样的。 伽利略对钟摆的运动有了重大发现。 这一发现使一种更好的测量时间的仪器——钟摆成为可能。