'Or suns,' said Ponder.

'Don't be silly, Stibbons, they're far too large for that. I'd hate to see one of those floating over the clouds,' said the Lecturer in Recent Runes.

'I said there was far too much gas,' the Archchancellor went on. 'That wraps it up, then.'

'I wonder,' said the Senior Wrangler.

'What?' said the Dean.

'Well, at least we've got some heat in there ... and there nothing like a good furnace for improving matters.'

'Good point,' said Ridcully. 'Look at bronze, you can make that out of just about anything. And we could burn off some of the rub­bish. All right, you fellows, help me dump more of the stuff in it...'

Around about teatime, the first of the furnaces exploded, just as happened every day down at the Alchemists' Guild.

'Ye gods,' said Ridcully, watching the shapes in the omniscope.

'Yo?' said the Dean.

'We've made new elements!'

'Keep it down, keep it down!' hissed the Senior Wrangler.

'There's iron ... silicon ... we've got rocks, even ...'

'We're going to be in serious trouble if the alchemists' guild finds out,' said the Lecturer in Recent Runes. 'You know we're not supposed to do that stuff.'

'This is a different universe,' said Ridcully. He sighed. 'You have to blow things up to get anything useful.'

'I see politicium is still there in large quantities, then,' said the Senior Wrangler.

'I meant that this is a godless reality, gentlemen.'

'Excuse me, the Dean began.

'I shouldn't look so smug if I was you, Dean,' said Ridcully. 'Look at the place. Everything wants to spin, and sooner or later you have balls.'

'And we're getting the same sort of stuff that we get here, isn't that strange?' said the Senior Wrangler, as Mrs Whitlow the house­keeper came in with the tea trolley.

'I don't see why,' said the Dean. 'Iron's iron.'

'Well, it's a whole new universe, so you'd expect new things, wouldn't you? Metals like Noggo, perhaps, or Plinc.'

'What's your point, Senior Wrangler?'

'I mean, take a look at the thing now ... all those burning explod­ing balls do look a bit like the stars, don't they? I mean they're vaguely familiar. Why isn't it a universe full of tapioca, say, or very large chairs? I mean, if nothing wants to be something, why can't it be anything?'

The wizards stirred their tea and thought about this.

'Because,' said the Archchancellor, after a while.

'That's a good answer, sir,' said Ponder, as diplomatically as he could, 'But it does rather close the door on further questions.'

'Best kind of answer there is, then.'

The Senior Wrangler watched Mrs Whitlow produce a duster and polish the top of the Project.

'"As Above, So Below",' said Ridcully, slowly.

'Pardon?' said the Senior Wrangler.

'We're forgetting our kindergarten magic, aren't we? It's not even magic, it's a ... a basic rule of everything. The project can't help being affected by this world. Piles of sand try to look like moun­tains. Men try to act like gods. Little things so often appear to look like big things made smaller. Our new universe, gentlemen, will do its crippled best to look like ours. We should not be surprised to see things that look hauntingly familiar. But not as good, obviously.'

The inner eye of HEX gazed at a vast cloud of mind. HEX couldn't think of a better word. It didn't technically exist yet, but HEX could sense the shape. It had hints of many things, of tradition, of libraries, of rumour ...

There had to be a better word. HEX tried again.

On Discworld, words had real power. They had to be dealt with carefully.

What lay ahead had the shape of intelligence, but only in the same way that a sun had the shape of something living out its brief life in a puddle of ditchwater.

Ah ... eJrtelligence would do for now.

HEX decided to devote part of its time to investigating this inter­esting thing. It wanted to find out how it had developed, what kept it going ... and why, particularly, a small but annoying part of it seemed to believe that if everyone sent five dollars to the six names at the top of the list, everyone would become immensely rich.

(or at least we went to Woodstock)

IRON'S IRON.' BUT IS IT? Or is iron made from other things?

According to Empedocles, an ancient Greek, everything in the universe was a combination of four ingredients: earth, air, fire, and water. Set light to a stick and it burns (showing that it contains fire), gives off smoke (showing that it contains air), exudes bubbly liquids (show­ing that it contains water), and leaves a dirty heap of ash behind (showing that it contains earth). As a theory, it was a bit too simple-minded to survive for long, a couple of thousand years at best. Things moved more slowly in those days, and Europe, at least, was more interested in making sure that the peasants didn't get above their station and copying out bits of the Bible by hand in as labori­ous and colourful a manner as possible.

The main technological invention to come out of the Middle Ages was a better horse collar.

Empedocles's theory was a distinct advance on its predecessors. Thales, Heraclitus, and Anaximenes all agreed that everything was made from just one basic 'principle', or element, but they dis­agreed completely about what it was. Thales reckoned it was water, Heraclitus preferred fire, and Anaximenes was willing to bet the farm on air. Empedocles was a wishy-washy synthesist who thought everyone had a valid point of view: if alive today he would definitely wear a bad tie.

The one good idea that emerged from all this was that 'elemen­tary' constituents of matter should be characterized by having simple, reliable properties. Earth was dirty, air was invisible, fire burned, and water was wet.

Aside from the superior horse collar, the medieval period did act as a breeding ground for what eventually turned into chemistry. For centuries the nascent science known as alchemy had flourished; people had discovered that some strange things happen when you mix substances together and heat them, or pour acid over them, or dissolve them in water and wait. You could get funny smells, bangs, bubbles, and liquids that changed colour. Whatever the universe was made of, you could clearly convert some of it into something else if you knew the right trick. Maybe a better word is 'spell', for alchemy was akin to magic, lots of special recipes and rituals, many of which actually worked, but no theory about how it all fitted together. The big goals of alchemy were spells, recipes, for things like the Elixir of Life, which would make you live forever, and How to Turn Lead Into Gold, which would give you lots of money to finance your immortal lifestyle. Towards the end of the Middle Ages, alchemists had been messing about for so long that they got quite good at it, and they started to notice things that didn't fit the Greeks' theory of four elements. So they introduced extra ones, like salt and sulphur, because these substances also had simple, reliable properties, different from being dirty, invisible, burning, or wet. Sulphur, for example, was combustible (though not actually hot, you understand) and salt was incombustible.

By 1661 Robert Boyle had sorted out two important distinc­tions, putting them into his book The Sceptical Chymist. The first distinction was between a chemical compound and a mixture. A mixture is just different things, well, mixed up. A compound is all the same stuff, but whatever that stuff is, it can be persuaded to come apart into components that are other kinds of stuff- provided you heat it, pour acid on it, or find some other effective treatment. What you can't do is sort through it and find a different bit; for a mixture you can, although you might need very good eyesight and tiny fingers. The second distinction was between compounds and elements. An element really is one kind of stuff: you can't separate it into different components.