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 the time aspect of memory there is simultaneity as well as sequence—time ceases to be linear and becomes plane. More remarkable illustrations of the sublimation of the time-sense are to be found in the phenomena of sleep and dreams.
"Oh, thou that sleepest, what is sleep?" asks the curious Leonardo. Modern psychological science has little to offer of a positive nature in answer to this world-old question, but it has at least effectively disposed of the absurd theories of the materialists who would have us believe that sleep is a mere matter of blood circulation or of intoxication by accumulation of waste products in the system. Sleep states are not abnormal, but part and parcel of the life existence of the individual. When a person is asleep he has only become unresponsive to the mass of