'Er. Shouldn't be too much of a problem,' he added. 'People used to think it was, but I'm pretty sure it's all a matter of energy absorption and attention to relative velocities.'

The statement was followed with the kind of mystified and suspicious silence that generally succeeded one of his remarks.

'Relative velocities,' said Ridcully.

'Yes, Archchancellor.' Ponder looked down at his prototype slide rule and waited. He knew that Ridcully would feel it necessary to add a comment at this point in order to demonstrate that he'd grasped something.

'My mother could move like lightning when—'

'I mean how fast things are going when compared to other things,' Ponder said quickly, but not quite quickly enough. 'We should be able to work it out quite easily. Er. On Hex.'

'Oh, no,' said the Lecturer in Recent Runes, pushing his chair back. 'Not that. That's meddling with things you don't understand.'

'Well we are wizards,' said Ridcully. 'We're supposed to meddle with things we don't understand. If we hung around waitin' till we understood things we'd never get anything done.'

'Look, I don't mind summoning some demon and asking it,' said the Lecturer in Recent Runes. 'That's normal. But building some mechanical contrivance to do your thinking for you, that's... against Nature. Besides,' he added in slightly less foreboding tones, 'last time you did a big problem on it the wretched thing broke and we had ants all over the place.'

'We've sorted that out,' said Ponder. 'We—'

'I must admit there was a ram's skull in the middle of it last time I looked,' said Ridcully.

'We had to add that to do occult transformations,' said Ponder, 'but—'

'And cogwheels and springs,' the Archchancellor went on.

'Well, the ants aren't very good at differential analysis, so—'