There then follows a long series of numbered paragraphs, in which Paley qualifies his argument more carefully, extends it to cases where, for instance, some parts of the watch are missing, and dismisses several objections to his reasoning. The second chapter takes up the story by describing a hypothetical `watch' that can produce copies of itself - a remarkable anticipation of the twentieth-century concept of a Von Neumann machine. There would still be good reason, Paley states, to infer the existence of a 'contriver'; in fact, if anything, the effect would be to enhance one's admiration for the contriver's skill. Moreover, the intelligent observer would reflect, that though the watch before him were, in some sense, the maker of the watch which was fabricated in the course of its movements, yet it was in a very different sense from that in which a carpenter, for instance, is the maker of a chair.

He continues to develop this thought, and disposes of one possible suggestion: that, just as a stone might always have existed, for all he knew, so a watch might have always existed. That is, there might have been a chain of watches, each made by its predecessor, going back infinitely far into the past, so that there never was any first watch. However, he tells us, a watch is very different from a stone: it is contrived. Perhaps stones could always have existed: who knows? But not watches. Otherwise we would have `contrivance, but no contriver; proofs of design, but no designer'. Rejecting this suggestion on various metaphysical grounds, Paley states: The conclusion which the first examination of the watch, of its works, construction, and movement, suggested, was, that it must have had, for the cause and author of that construction, an artificer, who understood its mechanism, and designed its use. This conclusion is invincible. A second examination presents us with a new discovery. The watch is found, in the course of its movement, to produce another watch, similar to itself: and not only so, but we perceive in it a system or organisation, separately calculated for that purpose. What effect would this discovery have, or ought it to have, upon our former inference? What, as hath already been said, but to increase, beyond measure, our admiration of the skill which had been employed in the formation of such a machine!

Well, we can all see where the good reverend is leading, and he homes in on his target in his third chapter. Instead of a watch, consider an eye. Not lying on a heath, but in an animal, which perhaps does lie on a heath. What he does say is: compare the eye to a telescope. There are so many similarities that we are forced to deduce that the eye was `made for vision', just as the telescope was. Some thirty pages of anatomical description reinforce the contention that the eye must have been designed for the purpose of seeing. And the eye is just one example: consider a bird, a fish, a silkworm, or a spider. Now, finally, Paley states explicitly what all his readers knew was coming from page one: Were there no example in the world of contrivance except that of the eye, it would be alone sufficient to support the conclusion which we draw from it, as to the necessity of an intelligent Creator.

There we have it, in a nutshell. Living creatures are so intricate, and function so effectively, and fit together so perfectly, that they can have arisen only by design. But design implies a designer. Ergo: God exists, and it was He who created Earth's magnificent panoply of life. What more is there to say? The proof is complete.

IT WAS THREE HOURS LATER ...

The senior wizards trod carefully in the High Energy Magic Building, partly because it wasn't their natural habitat, but also because most of the students who frequented it used the floor as a filing cabinet and, distressingly, as a larder. Pizza is quite hard to remove from a sole, especially the cheese.

In the background - always in the background in the High Energy Magic Building - was Hex, the university's thinking engine.

Occasionally, bits of it, or possibly `him', moved. Ponder Stibbons had long ago given up trying to understand how Hex worked. Possibly Hex was the only entity in the university who understood how Hex worked.

Somewhere inside Hex magic happened. Spells were reduced, not to their component candles and wands and chants, but to what they meant. It happened too fast to see, and perhaps too fast to understand. All that Ponder was certain about was that life was intimately involved. When Hex was thinking deeply there was a noticeable hum from the beehives along the back wall, where slots gave them access to the outside world, and everything completely ceased to work if the ant colony was removed from its big glass maze in the heart of the machine.

Ponder had set up his magic lantern for a presentation. He liked making presentations. For a brief moment in the chaos of the universe, a presentation made everything sound as if it was organised.

`Hex has run the history of Roundworld against the last copy,' he announced, as the last wizard sat down. 'He has found significant changes beginning in what was known as the nineteenth century. Slide, please, Rincewind.' There was some muffled grumbling behind the magic lantern and a picture of a plump and elderly lady appeared on the screen. `This lady is Queen Victoria, ruler of the Empire of the British.'

`Why is she upside down?' said the Dean.

`It could be because with a globe there is technically no right way up,' said Ponder. `But I'm hazarding that it got put in wrong. Next slide, please. With care.' Grumble, click. 'Ah, yes, this is a steam engine. The reign of Victoria was notable for great developments in science and engineering. It was a very exciting time. Except ... next slide, please.' Grumble, click.

`Wrong slide, that man!' said Ridcully. `It's just blank.'

'Aha, no, sir,' said Ponder, gleefully. `That is a dynamic way of showing you that the period I just described turns out not, in fact, to have happened. It should have, but it didn't. On this version of the Globe, the Empire of the British did not become as big, and the other developments were all rather muted. The great wave of discovery flattened out. The world settled down to a period of stability and peace.'

`Sounds good to me,' said Ridcully, and got a chorus of `hear, hears' from the other wizards.

`Yes, Archchancellor,' said Ponder. `And, then again, no. Getting off the planet, remember? The big freeze in five hundred years' time? No land life form surviving that was bigger than a cockroach?'

`No one bothered about that?' said Ridcully.

`Not until it was too late, sir. In that world as we left it, the first humans walked on the Moon less than seventy years after they flew at all.'

Ponder looked at their blank faces.

`Which was quite an achievement,' he said.

`Why? We've done that,' said the Dean.

Ponder sighed. `Things are different on a globe, sir. There are no broomsticks, no magic carpets, and going to the Moon is not just a case of pushing off over the edge and trying to avoid the Turtle on the way down.'

`How did they do it, then?' said the Dean.

`Using rockets, sir.'

`The things that go up and explode with lots of coloured lights?'

`Initially, sir, but fortunately they found out how to stop them doing that. Next slide, please ...' A picture that might have been a pair of old-fashioned pantaloons appeared on the screen. `Ah, this is our old friend, the Trousers of Time. We all know this. It's what you get when history goes two ways. What we have to do now is find out why they split. That means I shall have to-'

`Are we near the point where you mention quantum?' said Ridcully, quickly.