The appreciation of the distance of an event in time does not, however, wholly depend on the character of this movement of imagination.  Just as the apparent distance of a visible object depends inter alia on the distinctness of the retinal impression, so the apparent temporal remoteness of a past event depends in part on the degree of intensity and clearness of the mnemonic image.  This is seen even in the case of those images which we are able distinctly to localize in the time-perspective.  For a series of exciting experiences intervening between the present and a past event appears not only directly to add to our sense of distance by constituting an apparently long interval, but indirectly to add to it by giving an unusual degree of faintness to the recalled image.  An event preceding some unusually stirring series of experiences gets thrust out of consciousness by the very engrossing nature of the new experiences, and so tends to grow more faint and ghost-like than it would otherwise have done.

The full force of this circumstance is best seen in the fact that a very recent event, bringing with it a deep mental shock and a rapid stirring of wide tracts of feeling and thought, may get to look old in a marvellously short space of time.  An announcement of the loss of a dear friend, when sudden and deeply agitating, will seem remote even after an hour of such intense emotional experience.  And the same twofold consideration probably explains the well-known fact that a year seems much shorter to the adult than to the child.  The novel and comparatively exciting impressions of childhood tend to fill out time in retrospect, and also to throw back remote events into a dimly discernible region.

Now, this same circumstance, the degree of vividness or of faintness of the mnemonic image, is that which determines our idea of distance when the character of the intervening experiences produces no appreciable effect.[124] This is most strikingly illustrated in those imperfect kinds of recollection in which we are unable to definitely localize the mnemonic image.  To the consideration of these we will now turn.

B. Indefinite Localization.

Speaking roughly and generally, we may say that the vividness of an image of memory decreases in proportion as the distance of the event increases.  And this is the rule which we unconsciously apply in determining distance in time.  Nevertheless, this rule gives us by no means an infallible criterion of distance.  The very fact that different people so often dispute about the dates and the order of past events experienced in common, shows pretty plainly that images of the same age tend to arise in the mind with very unequal degrees of vividness.