Rincewind sniffed. This rock smelt of frying. The smell seemed to be coming from up ahead, and appealed straight to his stomach.

‘Can you smell anything?’ he said.

‘I think it’s bacon,’ said Twoflower.

‘I hope it’s bacon,’ said Rincewind, ‘because I’m going to eat it.’ He stood up on the trembling stone and tottered forward into the clouds, peering through the wet gloom.

At the front or leading edge of the rock a small druid was sitting crosslegged in front of a small fire. A square of oilskin was tied across his head and knotted under his chin. He was poking at a pan of bacon with an ornamental sickle.

‘Um,’ said Rincewind. The druid looked up, and dropped the pan into the fire. He leapt to his feet and gripped the sickle aggressively, or at least as aggressively as anyone can look in a long wet white nightshirt and a dripping headscarf.

‘I warn you, I shall deal harshly with hijackers,’ he said, and sneezed violently.

‘We’ll help,’ said Rincewind, looking longingly at the burning bacon. This seemed to puzzle the druid who, to Rincewind’s mild surprise, was quite young; he supposed here had to be such things as young druids, theoretically, it was just that he had never imagined them.

‘You’re not trying to steal the rock?’ said the druid, lowering the sickle a fraction.

‘I didn’t even know you could steal rocks,’ said Rincewind wearily.

‘Excuse me,’ said Twoflower politely, ‘I think your breakfast is on fire.’

The druid glanced down and flailed ineffectually at the flames. Rincewind hurried forward to help, there was a fair amount of smoke, ash and confusion, and the shared triumph of actually rescuing a few pieces of rather charred bacon did more good than a whole book on diplomacy.

‘How did you get here, actually?’ said the druid. ‘We’re five hundred feet up, unless I’ve got the runes wrong again.’

Rincewind tried not to think about height. ‘We sort of dropped in as we were passing,’ he said.

‘On our way to the ground,’ Twoflower added.

‘Only your rock broke our fall,’ said Rincewind. His back complained. Thanks,’ he added.

‘I thought we’d run into some turbulence a while back,’ said the druid, whose name turned out to be Belafon. That must have been you.’ He shivered. ‘It must be morning by now,’ he said. ‘Sod the rules, I’m taking us up. Hang on.’

‘What to?’ said Rincewind.

‘Well, just indicate a general unwillingness to fall off,’ said Belafon. He took a large iron pendulum out of his robe and swung it in a series of baffling sweeps over the fire.

Clouds whipped around them, there was a horrible feeling of heaviness, and suddenly the rock burst into sunlight.

It levelled off a few feet above the clouds, in a cold but bright blue sky. The clouds that had seemed chillingly distant last night and horribly clammy this morning were now a fleecy white carpet, stretching away in all directions; a few mountain peaks stood out like islands. Behind the rock the wind of its passage sculpted the clouds into transient whirls. The rock—

It was about thirty feet long and ten feet wide, and blueish.

‘What an amazing panorama,’ said Twoflower, his eyes shining.

‘Um, what’s keeping us up?’ said Rincewind.

‘Persuasion,’ said Belafon, wringing out the hem of his robe.

‘Ah,’ said Rincewind sagely.

‘Keeping them up is easy,’ said the druid, holding up a thumb and squinting down the length of his arm at a distant mountain, The hard part is landing.’

‘You wouldn’t think so, would you?’ said Twoflower.

‘Persuasion is what keeps the whole universe together,’ said Belafon. ‘It’s no good saying it’s all done by magic.’

Rincewind happened to glance down through the thinning cloud to a snowy landscape a considerable distance below. He knew he was in the presence of a madman, but he was used to that; if listening to this madman meant he stayed up here, he was all ears.

Belafon sat down with his feet dangling over the edge of the rock.

‘Look, don’t worry,’ he said. ‘If you keep thinking the rock shouldn’t be flying it might hear you and become persuaded and you will turn out to be right, okay? It’s obvious you aren’t up to date with modern thinking.’

‘So it would seem,’ said Rincewind weakly. He was trying not to think about rocks on the ground. He was trying to think about rocks swooping like swallows, bounding across landscapes in the sheer joy of levity, zooming skywards in a—

He was horribly aware he wasn’t very good at it.

The druids of the Disc prided themselves on their forward-looking approach to the discovery of the mysteries of the Universe. Of course, like druids everywhere they believed in the essential unity of all life, the healing ower of plants, the natural rhythm of the seasons and the burning alive of anyone who didn’t approach all this in the right frame of mind, but they had also thought long and hard about the very basis of creation and had formulated the following theory:

The universe, they said, depended for its operation on the balance of four forces which they identified as charm, persuasion, uncertainty and bloody-mindedness.

Thus it was that the sun and moon orbited the disc because they were persuaded not to fall down, but didn’t actually fly away because of uncertainty. Charm allowed trees to grow and bloody-mindedness kept them up, and so on.

Some druids suggested that there were certain flaws in this theory, but senior druids explained very pointedly that there was indeed room for informed argument, the cut and thrust of exciting scientific debate, and basically it lay on top of the next solstice bonfire.

‘Ah, so you’re an astronomer?’ said Twoflower.

‘Oh no,’ said Belafon, as the rock drifted gently around the curve of a mountain, I’m a computer hardware consultant.’

‘What’s a computer hardware?’

‘Well, this is,’ said the druid, tapping the rock with a sandalled foot.’Part of one, anyway. It’s a replacement. I’m delivering it. They’re having trouble with the big circles up on the Vortex Plains. So they say, anyway; I wished I had a bronze tore for every user who didn’t read the manual.’ He shrugged.

‘What use is it, then, exactly?’ asked Rincewind. Anything to keep his mind off the drop below.

‘You can use it to—to tell you what time of year it is,’ said Belafon.

‘Ah. You mean if it’s covered in snow then it must be winter?’

‘Yes. I mean no. I mean, supposing you wanted to know when a particular star is going to rise —’

‘Why?’ said Twoflower, radiating polite interest.

‘Well, maybe you want to know when to plant your crops,’ said Belafon, sweating a little, ‘or maybe—’

‘I’ll lend you my almanac, if you like,’ said Twoflower.

‘Almanac?’

‘It’s a book that tells you what day it is,’ said Rincewind wearily. ‘It’d be right up your leyline.’

Belafon stiffened. ‘Book?’ he said. ‘Like, with paper?’

‘Yes.’

That doesn’t sound very reliable to me,’ said the druid nastily. ‘How can a book know what day it is? Paper can’t count.’

He stamped off to the front of the rock, causing it to wallow alarmingly. Rincewind swallowed hard and beckoned Twoflower closer.

‘Have you ever heard of culture shock?’ he hissed.

‘What’s that?’

‘It’s what happens when people spend five hundred years trying to get a stone circle to work properly and then someone comes up with a little book with a page for every day and little chatty bits saying things like "Now is a good time to plant broad beans" and "Early to rise, early to bed, makes a man healthy, wealthy and dead," and do you know what the most important thing to remember about culture shock.’ Rincewind paused for breath, and moved his lips silently trying to remember where the sentence had got to, ‘is?’ he concluded.