tand these errors of mnemonic perspective, we shall
have to inquire more closely than we have yet done into the
circumstances which customarily determine our idea of the degree of
propinquity or of remoteness of a past event. And first of all, we will
take the case of a complete act of recollection when the mind is able to
travel back along an uninterrupted series of experiences to a definitely
apprehended point. Here there would seem, at first sight, to be no room
for error, since this movement of retrospective imagination may be said
to involve a direct measurement of the distance, just as a sweep of the
eye over the ground between a spectator and an object affords a direct
measurement of the intervening space.

Modern science, however, tells us that this mode of measurement is by no
means the simple and accurate process which it at first seems to be. In
point of fact, there is something like a constant error in all such
retrospective measurement. Vierordt has proved experimentally, by making
a person try to reproduce the varying time-intervals between the
strokes of the pendulum of a metronome, that when the interval is a very
small one, we uniformly tend to exaggerate it in retrospection; when a
large one, to regard it, on the contrary, as less than it actually
was.[117]

A mere act of reflection will convince any one that when he tries to
conceive a very small interval, say a quarter of a second, he is likely
to make it too great. On the other hand, when we try to conceive a year,
we do not fully grasp the whole extent of the duration. This is proved
by the fact that merely by spending more time over the attempt, and so
recalling a larger number of the details of the period, we very
considerably enlarge our first estimate of the duration. And this leads
to great discrepancies in the appreciation of the relative magnitudes of
past sections of time. Thus, as Wundt observes, though in retrospect
both a month and a year seem too short, the latter is relatively much
more shortened than the former.[118]

The cause of this constant error in the mode of reproducing durations
seems to be connected with the very nature of the reproductive act. It
must be borne in mind that this act is itself, like the experience which
it represents, a mental process, occupying time, and that consequently
it may very possibly reflect its time-character on the resulting
judgment. Thus, since it certainly takes more than a quarter of a second