to pass in imagination from one impression to another, it may be that we
tend to confound this duration with that which we try to represent.
Similarly, the fact that in the act of reproductive imagination we
under-estimate a longer interval between two impressions, say those of
the slow beats of a colliery engine, may be accounted for by the
supposition that the imagination tends to pass from the one impression
to the succeeding one too rapidly.[119]

The gross misappreciation of duration of long periods of time, while it
may illustrate the principle just touched on, clearly involves the
effect of other and more powerful influences. A mere glance at what is
in our mind when we recall such a period as a month or a year, shows
that there is no clear concrete representation at all. Time, it has been
often said, is known only so far as filled with concrete contents or
conscious experiences, and a perfect imagination of any particular
period of past time would involve a retracing of all the successive
experiences which have gone to make up this section of our life. This, I
need not say, never happens, both because, on the one hand, memory does
not allow of a complete reproduction of any segment of our experience,
and because, on the other hand, such an imaginative reproduction, even
if possible, would clearly occupy as much time as the experience
itself.[120]

When I call up an image of the year just closing, what really happens is
a rapid movement of imagination over a series of prominent events, among
which the succession of seasons probably occupies the foremost place,
serving, as I have remarked, as a framework for my retrospective
picture. Each of the events which I thus run over is really a long
succession of shorter experiences, which, however, I do not separately
represent to myself. My imaginative reproduction of such a period is
thus essentially a greatly abbreviated and symbolic mode of
representation. It by no means corresponds to the visual imagination of
a large magnitude, say that of the length of sea horizon visible at any
one moment, which is complete in an instant, and quite independent of a
successive imagination of its parts or details. It is essentially a very
fragmentary and defective numerical idea, in which, moreover, the real
quantitative value of the units is altogether lost sight of.

Now, it seems to follow from this that there is something illusory in
all our recallings of long periods of the