Our estimate of duration, when it is over, depends less on this circumstance of having attended to its transition than on other considerations.  Wundt, indeed, seems to think that the feeling accompanying the actual flow of time has no effect on the surviving subjective appreciation; but this must surely be an error, since our mental image of any period is determined by the character of its contents.  Wundt says that when once a tedious waiting is over, it looks short because we instantly forget the feeling of tedium.  My self-observation, as well as the interrogation of others, has satisfied me, on the contrary, that this feeling distinctly colours the retrospective appreciation.  Thus, when waiting at a railway station for a belated train, I am distinctly aware that each quarter of an hour looks long, not only as it passes, but when it is over.  In fact, I am disposed to express my feeling as one of disappointment that only so short an interval has passed since I last looked at my watch.

Nevertheless, I am ready to allow that, though a feeling of tedium, or the contrary feeling of irritation at the rapidity of time, will linger for an appreciable interval and colour the retrospective estimate of time, this backward view is chiefly determined by other considerations.  As Wundt remarks, we have no sense of time’s slowness during sleep, yet on waking we imagine that we have been dreaming for an immensely long period.  This retrospective appreciation is determined by the number and the degree or intensity of the experiences, and, what comes very much to the same thing, by the amount of unlikeness, freshness, and discontinuity characterizing these experiences.

Time, as I have already hinted, is known under the form of a succession of different conscious experiences.  Unbroken uniformity would give us no sense of time, because it would give us no conscious experience at all.  Strictly speaking, there is no such thing as a perfectly uniform mental state extending through an appreciable duration.  In looking at one and the same object, even in listening to one and the same tone, I am in no two successive fractions of a second in exactly the same state of mind.  Slight alterations in the strength of the sensation,[123] in the degree or direction of attention, and in the composition of that penumbra of vague images which it calls up, occur at every distinguishable fraction of time.

This being so, it would seem to follow that the greater the number of clearly marked changes, and the more impressive and exciting these transitions, the fuller will be our sense of time.  And this is borne out by individual reflection.  When striking and deeply interesting events follow one another very rapidly, as when we are travelling, duration appears to swell out.