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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 the 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.

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This man is in training.

He is going to run a distance of one mile in the shortest possible time.

The fastest runner 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.

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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.

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There is a good story about the use the great Italian scientist Galileo one make 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.

Washing 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 the turns, however far it went.

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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 motion of a pendulum.

Among other things this discovery made possible a better instrument for measuring time-the pendulum clock.

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Measuring how fast something is moving gives us the rate of motion.

This plane has gone 300 miles in half an hour.

Its rate was 600 m.p.h.

This man has walked two miles in half an hour.

He walking at a rate of four miles an hour.

Now he is standing.

He is not moving.

This man is working slowly.

His pay will be small if he is paid by the amount of work he does in a day.

This other man is working quickly.

His pay will be high if his paid by amount of work done in a day.

The two commonest ways of paying a worker are by the hour and by the amount of work done.

piecework is work paid by the amount done.

For different sorts of work rates of pay may be different.

Sometimes rates for the same sort of work are different in different places.

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In different countries different sorts of money may be used.

In the U.S.A. and Canada people are paid in dollars;

in the U.K. they are paid in pounds.

The rate of exchange between the U.S.A. dollar and the pound in 2004 was about $1.76 to ￡1.

You could exchange a pound for $1.76.

Here are some other rates of exchange;they are for the business week 16-August 20,2004

A table of exchange rates is printed in the newspaper.

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When we move about from one country to another we sometimes have to change our money,

we sometimes have to change our watches and sometimes we change both.

When we change our watches we move the hands forward and back:

forward if we are going east and back if we are going west.

Here is a map giving time lines across the Pacific Ocean.

In the days when Galileo used his pulse as a timekeeper, most people did not even know that the earth was round.

They knew no more about the journey of the earth around the sun than they did about the journey of their blood stream through their bodies.

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But,two thousand years before Galileo, there were Egyptians and Greeks who knew more than a little about the motions of the sun and stars and the angles between them at different times.

Some few Greeks even knew than the earth is not flat, as it seems,but round like a ball.

One of them even said than it was about 25,000 miles round, which it is,and that the earth moved round the sun while turning on itself.

It is from the Greek language (sometimes through Latin and French) that many of the words used in science have come.

For example:

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But for another two thousand years most people went on thinking that the earth was flat like a large plate with the sun and stars journeying round it.

How was the idea that the earth is not flat but round like a ball proved true in the end?

Sailing men went out in their ships to find a way by water from Europe to India and China.

Though some ships from the north of Europe had sailed west to parts of America in the tenth century, most of Europe had no knowledge of the land across the Atlantic.

Men like Marco Polo had gone east to India and China,much of the way by land,

long before Columbus in 1492, went sailing west with the idea that he could get round to the Far East by water.