has no real existence. They taught you that? Neither has a
mathematical plane. These things are mere abstractions.'

'That is all right,' said the Psychologist.

'Nor, having only length, breadth, and thickness, can a cube have a
real existence.'

'There I object,' said Filby. 'Of course a solid body may exist. All
real things--'

'So most people think. But wait a moment. Can an _instantaneous_
cube exist?'

'Don't follow you,' said Filby.

'Can a cube that does not last for any time at all, have a real
existence?'

Filby became pensive. 'Clearly,' the Time Traveller proceeded, 'any
real body must have extension in _four_ directions: it must have
Length, Breadth, Thickness, and--Duration. But through a natural
infirmity of the flesh, which I will explain to you in a moment, we
incline to overlook this fact. There are really four dimensions,
three which we call the three planes of Space, and a fourth, Time.
There is, however, a tendency to draw an unreal distinction between
the former three dimensions and the latter, because it happens that
our consciousness moves intermittently in one direction along the
latter from the beginning to the end of our lives.'