Ponder looked at his notes, and then surveyed the faculty.

'Ahem ...' he began.

'I've got a throat sweet somewhere,' said the Senior Wrangler, patting his pockets.

Ponder looked at his notes again, and a horrible sense of hope­lessness overcame him. He realized that he could explain thaumic fission very well, provided that the person listening already knew all about it. With the senior wizards, though, he'd need to explain the meaning of every word. In some cases this would mean words like 'the' and 'and'.

He glanced down at the water jug on his lectern, and decided to extemporize.

Ponder held up a glass of water.

'Do you realize, gentlemen,' he said, 'that the thaumic potential in this water ... that is, I mean to say, the magical field generated by its narrativium content which tells it that it is water and lets it keep on being water instead of, haha, a pigeon or a frog ... would, if we could release it, be enough to move this whole university all the way to the moon?'

He beamed at them.

'Better leave it in there, then,' said the Chair of Indefinite Studies.

Ponder's smile froze.

'Obviously we cannot extract all of it,' he said, 'But we...'

'Enough to get a small part of the university to the moon?' said the Lecturer in Recent Runes.

'The Dean could do with a holiday,' said the Archchancellor.

'I resent that remark, Archchancellor'

'Just trying to lighten the mood, Dean.'

'But we can release just enough for all kinds of useful work,' said Ponder, already struggling.

'Like heating my study,' said the Lecturer in Recent Runes. 'My water jug was iced up again this morning.'

'Exactly!' said Ponder, striking out madly for a useful Lie-to-Wizards. 'We can use it to boil a great big kettle! That's all it is! It's perfectly harmless! Not dangerous in any way! That's why the University Council let me build it! You wouldn't have let me build it if it was dangerous, would you?'

He gulped down the water.

As one man, the assembled wizards took several steps back­wards.

'Let us know what it's like up there,' said the Dean.

'Bring us back some rocks. Or something,' said the Lecturer in Recent Runes.

'Wave to us', said the Senior Wrangler. 'We've got quite a good telescope.'

Ponder stared at the empty glass, and readjusted his mental sights once more.

'Er, no,' he said. 'The fuel has to go inside the reacting engine, you see. And then ... and then ...'

He gave up.

'The magic goes round and round and it comes up under the boiler that we have plumbed in and the university will then be lovely and warm,' he said. 'Any questions?'

'Where does the coal go?' said the Dean, 'It's wicked what the dwarfs are charging these days.'

'No, sir. No coal. The heat is ... free,' said Ponder. A little bead of sweat ran down his face.

'Really?' said the Dean. 'That'll be a saving, then, eh, Bursar? Eh? Where's the Bursar?'

'Ah ... er ... the Bursar is assisting me today, sir,' said Ponder. He pointed to the high gallery over the court. The Bursar was standing there, smiling his distant smile, and holding an axe. A rope was tied around the handrail, looped over a beam, and held a long heavy rod suspended over the centre of the reaction engine.

'It is ... er ... just possible that the engine may produce too much magic,' said Ponder. 'The rod is lead, laminated with rowan wood. Together they naturally damp down any magical reaction, you see. So if things get too ... if we want to settle things down, you see, he just chops through the rope and it drops into the very centre of the reacting engine, you see.'

'What's that man standing next to him for?'

'That's Mr Turnipseed, my assistant. He's the backup fail-safe device.'

'What does he do, then?'

'His job is to shout "For gods' sakes cut the rope now!" sir.'

The wizard nodded at one another. By the standards of Ankh-Morpork, where the common thumb was used as a temperature measuring device, this was health and safety at work taken to extremes.

'Well, that all seems safe enough to me,' said the Senior Wrangler.

'Where did you get the idea for this, Mister Stibbons?' said Ridcully.

'Well, er, a lot of it is from my own research, but I got quite a few leads from a careful reading of the Scrolls of Loko in the Library, sir.' Ponder reckoned he was safe enough there. The wizards liked ancient wisdom, provided it was ancient enough. They felt wisdom was like wine, and got better the longer it was left alone. Something that hadn't been known for a few hundred years probably wasn't worth knowing.

'Loko ... Loko ... Loko,' mused Ridcully. 'That's up on Uberwald, isn't it?'

That's right, sir.'

'Tryin' to bring it to mind,' Ridcully went on, rubbing his beard. 'Isn't that where there's that big deep valley with the ring of moun­tains round it? Very deep valley indeed, as I recall.'

'That's right, sir. According to the library catalogue the scrolls were found in a cave by the Crustley Expedition...'

'Lots of centaurs and fauns and other curiously shaped magical whatnots are there, I remember reading.'

'Is there, sir?'

'Wasn't Stanmer Crustley the one who died of planets?'

'I'm not familiar with...'

'Extremely rare magical disease, I believe.'

'Indeed, sir, but…'

'Now I come to think about it, everyone on that expedition con­tracted something seriously magical within a few months of getting back,' Ridcully went on.

'Er, yes, sir. The suggestion was that there was some kind of curse on the place. Ridiculous notion, of course.'

'I somehow feel I need to ask, Mister Stibbons ... what chance is there of this just blowin' up and destroyin' the entire university?'

Ponder's heart sank. He mentally scanned the sentence, and took refuge in truth. 'None, sir.'

'Now try honesty, Mister Stibbons.' And that was the problem with the Archchancellor. He mostly strode around the place shout­ing at people, but when he did bother to get all his brain cells lined up he could point them straight at the nearest weak spot.

'Well ... in the unlikely event of it going seriously wrong, it ... wouldn't just blow up the university, sir'

'What would it blow up, pray?'

'Er ... everything, sir.'

'Everything there is, you mean?'

'Within a radius of about fifty thousand miles out into space, sir, yes. According to HEX it'd happen instantaneously. We wouldn't even know about it.'

'And the odds of this are ... ?'

'About fifty to one, sir.'

The wizards relaxed.

'That's pretty safe. I wouldn't bet on a horse at those odds,' said the Senior Wrangler. There was half an inch of ice on the inside of his bedroom windows. Things like this give you a very personal view of risk.