I would say it was a pretty safe bet that the one magic wish most people would like to be granted would be to be able to see into the future. I mean, think what it would mean: backing the right horse. But we can’t. We have to guess about tomorrow, and we have to act on that guess. And it’s never been any different. And that’s why following the trail from the past up to the emergence of the modern technology that surrounds us in our daily lives and affect our lives is rather like a detective story. Because at no time in the past did anybody who had anything to do with the business of inventing or changing things ever know what the full effects of his actions would be. He just went ahead and did what he did for his own reasons—like we do. That’s how change comes about. And it’s like a detective story because, if you follow the trail from the past up to a modern man-made object, the story is full of sudden twists and false clues and guesswork, and you never know where the story is heading until the very last minute.

This detective story starts in the eastern Mediterranean about 2,500 years ago, and it starts with the subject dear to most people’s hearts: money. And because that’s the way things go in history, it will end—as will all these programs—with something totally different. In this case, a modern day invention that affects the life of every man, woman, and child on Earth. Take yourself back, then, to a time when the Mediterranean was practically empty, when the ancient Greeks had only just turned up, and (together with the Phoenicians and the Egyptians) were about all there was, living in cities we would call villages. When, if you wanted to trade with somebody, it was a case of “Meet me in the market square and I’ll give you my vegetables if you give me your cloth.” You bartered because there was no such thing as cash.

And the reason we’ve come looking for clues in this particular city on the Mediterranean has to do with how cash was invented, and what happened as a result. The way it happened shows how change comes—as much as anything—by accident. Some time around 700 BC, in a place called Lydia (what is now modern Turkey), there was a river that washed gold down from the local mountains. And the local people used to pan it and melt it down for religious objects, jewelry, that kind of stuff. And then, in the riverbed, somebody came across this. It’s called a touchstone, and if you rub gold onto it, you get a streak. But if you rub gold mixed with silver or something else, you get a different kind of streak. See what that means? If that streak is pure gold and somebody’s trying to offload garbage onto you, well, you take what he calls gold and you rub it on the touchstone, and you can see immediately that what he says is gold isn’t up to your standard. Well, the Lydians went immediately into the business of standardizing their precious metals, and over the next 300 years or so, all over the eastern Mediterranean and in Persia, the habit spread of accepting metal instead of goods as payment. Because now you could trust the value of the metal. After that point, in any state or empire that had a mint making coins, the new money really stimulated trade.

By the time Alexander the Great was running everything from India to Italy, his coinage was accepted everywhere, and his world was like one giant marketplace. Well, in 331 BC, he decided to build a big commercial center to handle the flood of goods crisscrossing his empire. This was it, named after him: Alexandria. You could do two things here: get very rich and get yourself the best education in the world. You see, Alexandria had a library. And what a library! Its opening hours went on for maybe a thousand years. At its height, it had more than a half a million books. And that was it; I mean, if it wasn’t here, it wasn’t worth knowing about. And then, in the end, somebody burnt every single book. Nobody knows who. Fanatical Christians, fanatical Arabs—take your pick. Religion at work. Left nothing. Well, almost nothing.

Because the next clue in this particular historical detective story takes us down a hole. Of course, this was no ordinary hole. It led down to a kind of extra backup library. And since it wasn’t above ground to be destroyed, it’s still here. It’s a real honeycomb of tunnels down here, like a literary rabbit warren. Now, all the books were stored and cataloged, just like we do today, according to subject heading, and placed in niches like these. Of course, being a big seaport, the main interest was in nautical things like maps, geography books, aids to navigation, that sort of thing. And they were all written in ink on papyrus made from slivers of reed stuck flat together. And they came out like this, in the form of scrolls. Now, they got these scrolls either because the local scholars wrote them, or because they had a rather crafty law.

You see, if you came to Alexandria on a boat, and you owned a book, you had to lend it to the library to be copied. And sometimes, the copies were so good, the owners went off with the fakes and the library kept the original. This is a copy of one of the library’s bestsellers. Author: Claudius Ptolemy. Title: “All You Ever Wanted to Know About Calculation.” Thirteen volumes, all the astronomy that was known at the time. One of the volumes was a star catalog containing 1,022 stars. Look: here’s the name of the star, here’s the zodiac sign it’s in—Gemini, Sagittarius—here’s where it is in that zodiac. Is it northern or southern hemisphere? How many degrees east or west on the sky is it? And how bright is it?

Ptolemy did these squiggles about 150 AD. And they’re one of the great examples of an idea ahead of its time. Because one of the ways this was to be used by sailors to open up the world (in a way you’re going to see happening later in this program) wasn’t going to come for over 1,400 years. And as for the sailors pouring in and out of Alexandria in Ptolemy’s time—well, they just weren’t interested in charts of the sky. Some sailing astronomers might have used them in order to find out their position. Because, you see, if the tables told you that at a certain time a star should be in that position in the sky, and you actually saw it in that position, you could work backward, so to speak, to find out what position you’d have to be in in order to see it at that different angle.

But the sailors stuck to their maps and their winds. Because from the very beginning they’d used ships with the kind of sail that makes it hard to get into serious navigational problems; a square sail that only takes you the way the wind’s blowing—which is what they did right through the Roman period, with bigger ships and richer cargoes. Until suddenly, around 700 AD, the newly arrived Arab pirates gave one simple order: “Open your wallet and repeat after me: help yourself.” If you didn’t, they took it anyway. It became clear to even the dumbest merchant that the quickest way to lose a fortune was to put it all in one big fat cargo ship, so the Arabs could take the lot. Everybody started spreading the risk in smaller ships: less to be plundered in one go.

That switch to the use of smaller ships brought into general use something that would help Europeans colonize America centuries later. The very earliest picture we have of it comes from a manuscript written in the ninth century in Byzantium. It was a sail; the kind of sail that had previously only been used on smaller ships, and the kind of sail that you can find on a modern Arab dhow, like this one, today. Look at the shape. It’s triangular. Now, that is a lateen sail. And what you could do with a lateen sail was something you could never have done with the old Roman square sail. Look, suppose the wind is coming in this direction. With a lateen sail you can sail in any direction right up until you’re almost sailing against the wind, on either side of it. So on a long journey they would go, take the wind from this side, then they would tack and take the wind from this side, and then they would tack again, take the wind again from this side.

Mind you, it wasn’t something they enjoyed doing too much. I mean, look what it involves. Apart from the fact that with the ton of tackle you needed and a lot more crew to handle it, the worst bit came when the ship was just about to cross the wind, at which point you had to lift the spar right over the top of the mast. And doing that in rough weather was no picnic. Still, it was a lot better than going in the wrong direction.

Now, if you’re not a sailing buff, you may not be turned on by the lateen sail. But as you’ll see, it means a great deal more to you than you might think. See, although it was nice to be able to zigzag everywhere, sailing like that wasn’t the only thing that happened because of this canvas triangle. The lateen sail permitted one other thing. With it, you could leave port pretty well when you wanted to without having to wait for a wind that was going in the same direction you were. Now, that meant you would leave port more often. That meant there was more cargo on the move, more trade, more prosperity.

It’s probable that the Arabs introduced the lateen sail into Western Europe just about in time to play a major role in the recovery of the European economy after the chaos and confusion of the so-called Dark Ages. However, by about 1200, there was so much bulk cargo—like grain or crusaders going to the Holy Land—so much bulk cargo on the move that the ships had gotten very much bigger. And then they ran into another problem: the problem of steering. You see, up until that point, you steered with a couple of oars, one off either side of the stern. But by about 1200, the ships were so big that those oars just really weren’t feasible anymore. Which is why they probably picked up an idea from the Chinese that solved the problem. This: the stern-post rudder. With the stern-post rudder you could handle a ship of almost any size in almost any sea condition.

So by the thirteenth century, the Europeans had all the technology—the lateen sail, the old square sail, the stern-post rudder—to go anywhere they wanted to. They didn’t need to use it until 1453, when Constantinople fell to the Turks. And after that (if you wanted something from the Far East) it was either pay the price the Turks wanted for letting it come through their territory, or go get it yourself. Which is just what the Europeans did in the great sixteenth century voyages of discovery.

And it was now that the mariners began to use those star charts prepared in such detail by Claudius Ptolemy fourteen centuries before. This is the Golden Hinde, the ship that carried Sir Francis Drake around the world. It’s not unlike the earlier caravels that sailed with the great Portuguese navigators down ’round the southern tip of Africa, and then out across the Atlantic with Columbus in 1492. So what was it about these ships that meant that you could sail them at will to the ends of Earth? Well, look at the rigging.

Now, I know it looks like a confused mass of ropes, but if you look carefully, you’ll see the old square sail there on the front mast. And some of these ships had one, some two, sometimes even three masts carrying the square sails. But on the back-end there was a mast with a familiar triangle of shape of the lateen. And it was this mixture of sail that allowed you to cross an ocean anytime you wanted to. Look: here’s Spain and here’s the northern part of Africa, and over here there’s America and the Gulf and then South America. Now, in the area here off the coast, you get winds going in all sorts of direction; very variable. So you use a lateen sail to tack yourself into a position where the steady northeasterly trade winds (which you can pick up on the square sails) will take you straight across the Atlantic. When you want to come home you do the same thing the other way ’round: you tack through the variable winds until you pick up the westerlies, you put up the square sails, and the westerlies bring you all the way home.

Most of the maps they used at the time were made in Mallorca, and by the fourteenth century they were turning out portolan charts and updating them as explorers came back with more information. Now, the charts contained only what a sailor needed to know. No inland detail at all. Just details of the coastline, the names of the harbors, and these lines showing the directions of the major and minor winds along which you steered. The charts were very precise. And because the aim of the people using them is profit, they were also very secret.

But the thing that really gave Europe the world on a plate was that. The first reference we have to it is by an English monk around about 1200. It probably came from China via the Arabs to Europe. And early on, they would have used it like this. And the magnetized needle stuck through the straw would point north. And then, around about 1300, somebody probably in the maritime republic of Amalfi, south of Naples, hit on the idea of mounting the needle and putting a card on it, and on the card putting the wind directions, and putting the whole thing in a box.

The effect of the compass was electric—in more ways than one, as you’ll see. Firstly, it meant that you could go out sailing under cloudy skies, because you no longer needed the stars or the sun to steer by. And the immediate effect of that was to double the number of voyages, because now you could sail in the winter. So silk and spices from India, and gold and silver from America began to pour into Europe. And it wasn’t until enough men had sailed to enough places that they realized that the faithful compass was lying. There was true north (the north of the Pole Star) and there was the magnetic north. And depending where on Earth you were, that varied. And for a great mercantile empire like England, that was very bad news.

I suppose Shakespeare and the travel agents have done more than anybody else to give us our technicolor view of Elizabethan England, starring the queen herself as a kind of swashbuckler in pearls. The fact is, about all she had time for was bookkeeping. When she took the place over in 1558, it was national disaster week. The money was worthless. There was no money. There was plague. The cities were packed and stinking. Elizabeth appealed to the decent English middle class with their healthy desire for prestige, power, fun and games, and cash. Soon, anybody who wanted to be anybody was on the make. And none more than that famous bunch of privateering seadogs led by Drake, Raleigh, and Hawkins, who sailed the Atlantic looking for new American trade opportunities for England, setting up colonies, knocking off Spanish galleons, and doing it all with a kind of gutsy disregard for convention, that we describe today as criminal.

The privateers would bring back everything they could lay their hands on—even eskimos. And somewhere, in among the hustle and bustle and talk of adventure during the great feast days of places like Hampton Court, there must always have been some boor saying, “Hey, listen! You’ll never guess what happened to my compass needle last week!”

Now, the reason why all those pushy, ambitious, high-living upper middle class Elizabethans gave a damn about which way a compass needle pointed was because there were fantastic profits to be had in overseas trade. And if your needle let you down and you went off course, well, there was a pretty good chance you wouldn’t get home with all the lovely money. See, the problem with the needle was really quite simple. It didn’t always point in the same direction. And people had been saying that since 1492, when Columbus (on his way across to America) got to about here and panicked, because suddenly he realized that his needle wasn’t pointing at the North Star. And then, in 1580, when Sir Francis Drake got back from his around-the-world trip with enough gold and jewels pinched from one Spanish ship on its way home from Peru, to give his backers 4,700% profit, well, it was obviously time to do something about it. Because if his needle had let him down, look what they would have all lost!

So, in 1581, a compass maker called Robert Norman decided to look into the matter. And he did this. And he saw nothing happening, which was very odd. I mean, for a start he said, “If a needle is supposed to be attracted to the north, why doesn’t it move to the north instead of sitting in the middle of the bowl, doing nothing?” Well, Norman’s remarks attracted the interest of a certain William Gilbert, who wasn’t a sailor, he wasn’t a merchant. As a matter of fact, he was a well-heeled society doctor, eventually to become physician to the Queen. Now, like most other medics at the time, Gilbert knew a bit about magnetism because his profession was very much into metals. They had recently stopped an epidemic of syphilis by treating it with mercury in the form of mercuric oxide, this red powder. And magnetic metal was recommended for treating people with, because it was supposed to bring the disease out of them.

So, over a period of about, oh, eighteen years, Gilbert went home at the end of every day and fiddled around with natural magnets made of lodestone. And since the name of the game was to find out why the compass needle varied as it went around the Earth, he made his little magnets in the form of the Earth. And when he’d got plenty of them ready, he started his experiments, and brought anything he could think of in contact with his magnets—including, of course, a compass needle, which behaved exactly as he said it should: wherever he moved it, the needle pointed at the North Pole of his tiny magnet. So he reckoned that the Earth itself had to be a giant magnet with a magnetic north pole. And it was that that the compass pointed at, not the North Star.

What’s more, he said: if you leave one of these things alone, it turns once in a day. And therefore, the Earth must do exactly the same thing. And he said if the Earth is a magnet, that’s why what goes up must come down: because it’s attracted. In 1600, he wrote down everything he’d discovered in a vast book. And in doing so, he set in motion a train of events that would one day lead to one of the most frightening bits of technology in the modern world. He called his book De Magnete: “About the Magnet.”

Gilbert’s book was practically an overnight success in Europe. I mean, for a start, he was writing in Latin; so he didn’t have any translation problems. Most of the intellectuals around used Latin to work with. And then, look what he was saying: that the Earth is a giant magnet spinning in space, holding the moon with its power, surrounded by the vacuum of interplanetary space, and out there in that vacuum there are thousands and millions of unseen stars and planets. And he’s saying this in 1600? I mean, no wonder everybody went bananas about it. And the reason our detective story takes us next to this small town on the Danube in southern Germany is because of one man who got very excited by what Gilbert had said. His name is Otto Girica, and in 1653 he was here in Regensburg, commanded by the emperor to attend the coronation of his son. The coronation was the occasion for a great imperial shindig in the town, with dancing, and drinking and singing and, generally, whooping it up—rather like the annual Regensburg brawl going on here today.

In Regensburg, some of the more meaningful traditions haven’t changed a bit in hundreds of years. The sober citizens of Regensburg claim that it was here, in 1653, that Otto Girica did something quite amazing as a result of reading what Gilbert had said about the nothingness in interplanetary space. Here in Regensburg (they say) he took a hollow ball made of two hemispheres that fitted together, harnessed horses to each side of the ball, and however hard they pulled, the ball refused to come apart—although the two halves were not held together by any kind of joint. What kept them united was a mysterious force so powerful that horses couldn’t break it. They say that, after the experiment was over, Girica went on to astound the onlookers by opening a tiny hole in the ball, at which point it fell apart with a twist of his hands.

Now, whether or not that actually happened in Regensburg is neither here nor there. The fact is it caused a tremendous stir all over Europe. Because the mysterious force holding those hemispheres together is what Gilbert had been theorizing about in 1600 and what, in 1654, had only just been discovered: the vacuum. Put inside those hemispheres by the newly invented vacuum pump invented by Otto Girica—or rather, adapted by Otto Girica, because what he did was adapted one of these. You know what that is? It’s what you have to have handy if most of your buildings are made of wood. It’s a fire extinguisher. See? And Girica adapted it to suck air instead of water. And it was a very big hit with him: Ferdinand III, Holy Roman Emperor.

Ferdinand had taken the opportunity of his son’s coronation to invite all the princes and bishops and barons and city representatives from all over Germany to come here to this Reichstag Hall for several months of discussions on things like taxation and war and economic policy. Now, they all sat on these benches. And Ferdinand, of course, being emperor, sat up there on his throne. Anyway, towards the end of the sessions in 1654, Ferdinand asked Otto Girica—who was here, because he was mayor of Magdeburg—if he, Girica, would do some of the tricks that the emperor had heard he could do. And Girica, in this hall, obligingly used his vacuum pump to make vacuums in glass spheres. And then, he amazed the assembled company by showing them that mice suffocated in the vacuum, candles went out in it. If you rang a bell in it, you couldn’t hear the bell. And all sorts of other goodies. Ferdinand was so tickled by the whole thing that,when it was over, he asked if he could have all the apparatus. And being emperor, of course, he got it. Still, he did have the whole thing written up, which is how the rest of Europe got to hear about the vacuum pump.

Girica was a real dabbler. And he got very intrigued by one other thing he read in Gilbert’s book: the bit about some substances, like sulfur, attracting things. So Girica, quite solemnly, built himself this rather silly sulfur ball on a stick. And he spun it, and when he was spinning it, he rubbed it with his hand, like this. Now, the reason he did that is because he was looking for evidence of what we today would call gravity: why things stuck to the Earth and didn’t fly off into space. So when he wrote this experiment up, he went into great detail about things like: the ball would attract a piece of thread, and when the thread was in contact with the ball, the thread would attract things. Fortunately, he also mentioned something else about which he entirely missed the point. He said: if you spin the ball and rub it, and then take it out and hold it next to your ear, you hear a crack. And if you do it in the dark, the ball glows. Now, I said that was fortunate that he mentioned it, because his half-interested comments kicked off investigation into why the crack and the glow occurred. And that turned out to be electricity.

You know, the fascinating thing about moments like this in history is that they lead to so many places at once. We could, for instance, go forward from the vacuum pump to the investigation of air, to the discovery of oxygen, to finding out how the human lungs work, to modern respiratory medicine. Or we could go: vacuum pump, steam engine, locomotive. Or we could go: vacuum pump, investigation of gases, sending electric sparks through them to see what would happen, the cathode ray tube, modern radar. Or take the globe, the sulfur globe: the fact that the thread (when it was attached, you remember) carried the mysterious force away down the thread, led to people trying to do that deliberately to send the force down wire. That, in turn, led to the telegraph, and that, in turn, led to the telephone.

But for our purposes, let’s take the route that leads to one of modern society’s most horrifying inventions. And the next step on that route—from this seventeenth century government meeting forward into the future—takes us into the area of the Englishman’s favorite topic of conversation: the weather.

There was obviously some connection between Girica’s spark and lightning. So people got all excited about atmospheric electricity in general. Was there gunpowder in clouds? Was Irish fog more electric than other kinds? Interest centered on the unfortunate church bellrings, who (now you mentioned it) did tend to get electrocuted with monotonous regularity. Because one of their jobs was to ring the bell during storms.

But lightning got taken really seriously only when they realized it was doing this little trick. Gunpowder stores kept on doing this. Now, this was serious. It wasn’t just costing lives, it was costing money. It was these explosions that brought to public attention the ideas of the 15^th son of an American soapmaker who flew his kite in a storm to prove his point. Franklin reckoned the key solution was lightning rods, that would attract the negative electricity to their positive metal. Ships’ masts were like lightning rods, and it was a disgruntled navy that finally got the subject widened to include storms in general, when this happened.

In an attempt to warn their ships of storms, the Royal Navy started taking weather reports from them, as well as readings from their barometers. When the first of these collections was put together in 1861, they had the world’s first weather chart of an Atlantic depression—looking remarkably modern. On land the same thing started with stations reporting via the new telegraph.

Now, fortunately, all this seriousness was tinged with some of the peculiar insanity of the period, by the eagerness with which people now took to an amazing new invention, described just after it came out as infinitely the most extraordinary and magnificent discovery perhaps since creation. Now, you may feel that’s a bit exaggerated. But you can understand why people got so very lightheaded about it. It’s one of the symptoms you suffer from when you use it.

Going up on a balloon makes you feel like doing all sorts of daft things. By the middle of the nineteenth century, the balloon enjoyed the same kind of reputation the back seat of the motorcar did in the 1940s. It was rather often used for purposes for which it had not been originally designed. I mean, Frenchmen in particular would cruise along with their girlfriends, dropping empty champagne bottles on the gaping peasants below and returning to earth to announce their engagement. Mind you, some of it was all serious science. They took up barometers and thermometers, and cats and dogs and geese and ducks and sheep, and 200-pound ladies to observe their effect on the weather, and vice versa. And these intrepid pioneers enjoyed all the privileges of going to high altitude without oxygen: bleeding at the ears and eyes, nausea, vomiting, swelling of the head, and passing out.

Mind you, in spite of all that, they did learn things they never would have if they’d stayed on the ground, like: the temperature does not decrease steadily as you rise in the sky, and nor does the air pressure. Some of them stayed up for days, drifting along, enjoying the view, dropping notes by parachute that never seemed to say much other than, “everything going remarkably well”—including those who were never seen again.

By the late nineteenth century, what with all these airborne anemometers and reports from shipping and stations on the ground using the new electric telegraph, you could pick up a copy of your Times in the morning and get almost as good a forecast as you can today. The only disadvantage to all this high altitude information—which by now they regarded as vital—was that, sooner or later, when you ran out of hot air or hydrogen or food or champagne, you had to come down. What they needed was some way of staying at high altitude for as long as they liked. Which is why our story next takes us to a place you’d imagine they would have thought of long before; a place where you can stay at high altitude for as long as you like: the Highlands of Scotland.

On October the 17^th, 1883, this ancestral home at the bottom of a mountain was the venue for a get together by the cream of enlightened Scottish gentility to the mark the grand opening of a new weather station on top of the highest highland in Highlands, Ben Nevis. Refreshments were offered to the guests, and provisions were loaded for the journey to come by numerous factors and gillies and other members of the unpronounceable Scottish lower orders. It was a grand, ludicrous, overdone affair, in a way that all philanthropic Victorian public occasions were. In any other country of the world they’d have dropped the whole thing till the rain stopped. But this was nineteenth-century Scotland, and they were bent on serious matters. So they gritted their teeth and cheerfully did their duty as the rain filled up their bagpipes. After all, was the whole thing not being recorded for posterity?

The really nice thing about what science did to the Victorians was that it made them all lunatic in the same way. So the townspeople of Fort William also did their duty as the procession passed by getting soaked and waving silly flags as they were supposed to. At 9:00 am the party began their trek up the mountain, led by a single piper busking a catchy little Celtic number called Laquelle Sevarth de France. Why? I’ve never been able to find out. And the rain obligingly turned to sleet. So everybody could have what one is supposed to have when doing one’s duty: a thoroughly rotten time.

As more and more stations like Ben Nevis were set up and people could sit and look at the weather as it shifted and changed, they noticed that it made distinct patterns. So, in good Victorian style, they cataloged them, and in the 1890s came up with an official international cloud atlas, which gave clouds the names by which they’re known today. And this catalog of clouds is the next clue in our detective story. Because clouds caused something strange to happen at Ben Nevis.

You see, from the moment it opened, the station observers worked 24 hours a day. Each shift would send off regular reports on temperature, pressure, rain, and so on, and one of the reports they had to file would be about the clouds. And if you were on the dawn shift, you’d sometimes see the clouds in the valley do something very weird to your shadow. This is called a glory, and the strange thing about it is that the colors that appear in the halo don’t appear in the order they do in the rainbow, but the other way 'round.

At this point, events took the most extraordinary twist for the very mundane reason that the Ben Nevis observatory was short of cash. And so, because of that, they used to take on university students during their vacation to act as temporary unpaid observers while their own staff is on holiday. And in September 1894, one of those young men was a Cambridge physics graduate called Charles Wilson. This is him in much later life. And one morning, on Ben Nevis, Wilson saw a glory. And it turned him on so much that he decided to go back to Cambridge and make one for himself to find out how they worked. And that’s why our detective story brings us here.

Because the way Wilson did it—and how, in the long run, what he did came to effect the lives of every man, woman, and child on Earth—is illustrated in every museum of any size in the world. This one’s the Science Museum in London. And Wilson’s machine is here, hidden away among the thousands of other clues to mankind’s inventive genius. You know, considering the amazing thing it was to help give birth to, Wilson’s machine is really a rather unimpressive looking object. And although you’d expect to find it in the weather section (you know, because of the glory business and all that), that’s not where they put it. Usually, the first thing you see is what the machine actually did. Take a look in here. See those tiny cloud formations?

Now, Wilson wanted to make himself clouds because he wanted to make himself a glory to work on. So he built himself a cloud chamber in 1895. This is a later version, but the principle’s the same. Here is a sealed glass container, and fitting into the container below it there’s a piston inside that cylinder there, and underneath the piston there’s a gap. And leading from that gap is a tube through to this container, in which there’s a vacuum. Now, if you open the valve on that tube, the air underneath the piston whistles in here to fill the vacuum. That causes the piston to be jerked down very fast, and then this air up here has more space to fill—which it does, so it gets thinner, so its air pressure drops, and clouds form in here.

Now, at that time, everybody thought clouds formed because the tiny droplets of moisture condensed on little specs of dust in the air. But when Wilson cleared all the dust out of his machine, he still got clouds. Well, he reckoned it had to be something like radiation, because there wasn’t anything else. So, in 1896, he took some of the newly discovered x-rays and beamed them into his cloud chamber. And sure enough, they made clouds. But they made them in tiny streaks. “Well,” thought Wilson, “I’ve established a relationship between radiation and cloud, and that’s good enough for me.” So the dropped his work on the cloud chamber and went happily back to meteorology. And what he didn’t realize was that, inside that cloud chamber, he had triggered a scientific time bomb.

Over the next few years, Wilson, the magic cloud maker, got really turned on by really bad weather. And in particular, thunderstorms, and in very particular, the situations where things got really spectacularly bad. And so, he was to be seen risking life and limb by poking his instruments as close as possible to gigantic lightning strikes in order to find out how much power they gave off. And if you’re wondering why I’m telling you all this in the front end of a wartime B-29 bomber, well, one of the reasons is that, as a result of Wilson being so interested in lightning, wartime flying was safer—if that’s the right word to use. You see, when he found out what lightning was doing, he promptly told a friend of his, called Edward Appleton. Now, in 1915, what Appleton was trying to do is to find out why, when you turned on your new miracle machine called radio, what you got in your ear often, instead of long distance communication, was this. So Appleton decided to take a look at what the atmosphere did to radio waves. And in 1924 he finally shot some radio waves up in the sky, whereupon they promptly bounced back down again to the Earth. So he measured how long it took them to bounce back, and he said, “Hey, listen. There is a layer of something one hundred kilometers up there (I know because I measured it) that reflects radio waves.”

Now, all this measurement bit may seem just a touch dull to you, but it was music to the ears of another weatherman called Watson Watt, who at the time was trying to find out if he could use radio to locate storms—which, of course, now he could do. So he did it by using two radio transmitters, so that one would tell you a storm was in that direction so many miles, and another would tell you it was in that direction so many miles, and so you knew where the storm was.

“Okay,” I hear you say, “What has this got to do with an obsolete wartime bomber?” Well, all this radio wave super scientific stuff got the military very worked up, and in 1935 the British Air Ministry asked Watson Watt if he could make them a death ray—you know, destroy enemy planes in the sky. “No,” he said. “But, if radio waves will bounce off storms, they’ll also bounce off aircraft. So what about me giving you something that helps you find enemy aircraft in the sky, tell you how far away they are, and in what direction? We could call it radio detection and ranging, or R-A-D-A-R for short. We could also get to the returning echo from the aircraft to cause a beam of electrons going down a cathode ray tube to make a blip on a screen that had a range scale on it, so you could see the aeroplane and you could see where it was.” “Great idea,” they said. And this was the result: the radar that was used during the Second World War.

Today, because of radar, your holiday jet gets to its destination in safety, missing the storms and other holiday jets. And so we come almost to the end of our detective story. You remember how it all started 2,700 years ago when the touchstone told you you could trust somebody’s gold, and how that got all the merchants racing around the Mediterranean, and up to Russia, and out to India, and how, at the great trading port of Alexandria, the star tables got written, but not used by navigators until a new sail and rudder got things moving again in the middle ages, by which time they knew where they were going thanks to the compass—which, however, let them down, so William Gilbert tried to find out why using his magnetic models of the Earth that attracted everything. And how Girica in Regensburg got so excited by attraction, he tried spinning a sulfur ball. And how the sulfur ball causes sparks, and got everybody into atmospheric electricity, and the weather. And how, at the weather station on Ben Nevis, Wilson decided to make his cloud chamber, then got interested in storms, and helped to make radar happen.

I said we were almost at the end of our detective story. Not quite. The other reason we’re on board a B-29 is because one of those bombers also carried the other child of Wilson’s cloud chamber. Do you remember I had told you that he’d set off a scientific time bomb? Well, he did that because, back in 1911, he took this photograph of his little cloud streaks, and he showed it to a physicist called Ernest Rutherford, who said, “My god, you know what that is? That is a photograph of radiation particles knocking bits off an atom. And that means, we can see what we’re doing when we try to split the atom!” So Wilson’s photograph made it infinitely easier to produce a modern invention that helps us to cure one of the most deadly diseases known to mankind—or, if we choose, to wipe out all life on the face of the Earth. That invention was dropped by a B-29 at 9:15 on a sunny August morning in 1945 on Hiroshima. It was the atomic bomb.

Today, the nuclear bomb is like a sword of Damocles hanging over us. Will it fall again?