"As long as it's not the water of immortality I don't mind," said the distinguished Medical Man. "What is it?"
"Only a paradox," said the Psychologist.
The Time Traveler said nothing in reply, but smiled and began tapping his pipe upon the fender curb. This was the invariable presage of a dissertation.
"You have to admit that time is a spatial dimension," said the Psychologist, emboldened by immunity and addressing the Medical Man, "and then all sorts of remarkable consequences are found inevitable. Among others, that it becomes possible to travel about in time."
The Time Traveler chuckled. "You forget that I'm going to prove it experimentally."
"Let's have your experiment," said the Psychologist.
"I think we'd like the argument first," said Filby.