to the movements and positions of the planets, as night and winter
are related to the axial and orbital movements of the earth.

But there are other, and even more interesting, evidences of time
curvature in consciousness. These lead away into new regions which
it is our pleasure now to explore.




VI SLEEP AND DREAMS


SLEEP

Our space is called three-dimensional because it takes three
numbers--measurement in three mutually perpendicular directions--to
determine and mark out any particular point from the totality of
points. Time, as the individual experiences it, is called
one-dimensional for an analogous reason: one number is all that is
required to determine and mark out any particular event of a series
from all the rest. Now in order to establish a position in a space of
four dimensions it would be necessary to measure in _four_ mutually
perpendicular directions. Time curvature opens up the possibility of
a corresponding higher development in time: one whereby time would
be more fittingly symbolized by a plane than by a linear figure.
Indeed, the familiar mystery of memory calls for such a conception.
Memory is a carrying forward of the past into the present, and the
fact that we can recall a past event without mentally rehearsing
all the intermediate happenings in inverse order, shows that in