and men always have done so. I admit we move freely in two
dimensions. But how about up and down? Gravitation limits us there.'

'Not exactly,' said the Medical Man. 'There are balloons.'

'But before the balloons, save for spasmodic jumping and the
inequalities of the surface, man had no freedom of vertical
movement.'

'Still they could move a little up and down,' said the Medical Man.

'Easier, far easier down than up.'

'And you cannot move at all in Time, you cannot get away from the
present moment.'

'My dear sir, that is just where you are wrong. That is just where
the whole world has gone wrong. We are always getting away from the
present moment. Our mental existences, which are immaterial and have
no dimensions, are passing along the Time-Dimension with a uniform
velocity from the cradle to the grave. Just as we should travel _down_
if we began our existence fifty miles above the earth's surface.'

'But the great difficulty is this,' interrupted the Psychologist.
'You _can_ move about in all directions of Space, but you cannot
move about in Time.'

'That is the germ of my great discovery. But you are wrong to say
that we cannot move about in Time. For instance, if I am recalling
an incident very vividly I go back to the instant of its occurrence: