me 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.'

'That,' said a very young man, making spasmodic efforts to relight
his cigar over the lamp; 'that ... very clear indeed.'

'Now, it is very remarkable that this is so extensively overlooked,'
continued the Time Traveller, with a slight accession of
cheerfulness. 'Really this is what is meant by the Fourth Dimension,
though some people who talk about the Fourth Dimension do not know
they mean it. It is only another way of looking at Time. _There is
no difference between Time and any of the three dimensions of Space
except that our consciousness moves along it_. But some foolish
people have got hold of the wrong side of that idea. You have all
heard what they have to say about this Fourth Dimension?'

'_I_ have not,' said the Provincial Mayor.

'It is simply this. That Space, as our mathematicians have it, is
spoken of as having three dimensions, which one may call Length,
Breadth, and Thickness, and is always definable by reference to
three planes, each at right angles to the others. But some
philosophical people have been asking why _three_ dimensions
particularly--why not another direction at right angles to the other
three?--and have even tried to construct a Four-Dimension geometry.
Professor Simon Newcomb was expounding this to the New York
Mathematical Society only a month or so ago. You know how on a flat
surface, which has only two dimensions, we can represent a figure of
a three-dimensional solid, and similarly they think that by models
of three dimensions they could represent one of four--if they could
master the perspective of the thing. See?'

'I think so,' murmured the Provincial Mayor; and, knitting his
brows, he lapsed into an introspective state, his lips moving as one
who repeats mystic words. 'Yes, I think I see it now,' he said after
some time, brightening in a quite transitory manner.

'Well