Lord Vetinari gave him a severe look, but essayed a little wave.

‘Oh. How curious. What is your name, young man?’

‘Ponder Stibbons, sir. The new Head of Inadvisably Applied Magic, sir. You see, sir, the trick isn't to build an omniscope because, after all, that's just a development of the old-fashioned crystal ball. It's to get it to see what you want. It's like tuning a string, and if—’

‘Sorry, what applied magic?’ said the Patrician.

‘Inadvisably, sir.’ said Ponder smoothly, as if hoping that he could avoid the problem by driving straight through it. ‘Anyway… I think we can get it to the right area, sir. The power drain is considerable; we may have to sacrifice another gerbil.’

The wizards began to gather around the device.

‘Can you see into the future?’ said Lord Vetinari.

‘In theory yes, sir,’ said Ponder, ‘But that would be highly… well, inadvisable, you see, because initial studies indicate that the fact of observation would collapse the waveform in phase space.’

Not a muscle moved on the Patrician's face.

‘Pardon me, I'm a little out of date on faculty staff,’ he said. ‘Are you the one who has to take the dried frog pills?’

‘No, sir. That's the Bursar, sir,’ said Ponder. ‘He has to have them because he's insane, sir.’

‘Ah,’ said Lord Vetinari, and now he did have an expression. It was that of a man resolutely refraining from saying what was on his mind.

‘What Mr Stibbons means, my lord,’ said the Archchancellor, ‘is that there are billions and billions of futures that, er, sort of exist, d'yer see? They're all… the possible shapes of the future. But apparently the first one you actually look at is the one that becomes the future. It might not be one you'd like. Apparently it's all to do with the Uncertainty Principle.’