In the last section I attempted to explain the overestimation of short
filled spaces, and the underestimation of long filled spaces by active
touch, as the result of a double illusion arising from the differences
in the manner and amount of attention given to the two kinds of
spaces when they are held in immediate contrast. This explanation was
of course purely theoretical. I have thus far offered no experiments
to show that this double illusion of lengthening, on the one hand, and
shortening, on the other, does actually exist. I next made some simple
experiments which seemed to prove conclusively that the phenomenon
does not exist, or at least not in so important a way, when the time
factor is not permitted to enter.

In these new experiments the filled and the open spaces were compared
separately with optical distances. After the finger-tip was drawn over
the filled path, judgment was given on it at once by comparing it
directly with an optical distance. In this way the foreshortening
effect of time was excluded. In all these experiments it was seen that
the filled space was judged longer when the judgment was pronounced on
it at once than when an interval of time was allowed, either by
drawing the finger-tip out over the open space, as in the previous
experiment, or by requiring the subject to withhold his judgment until
a certain signal was given. Any postponement of the judgment resulted
in the disappearance of a certain amount of the illusion. The
judgments that were made rapidly and without deliberation were subject
to the strongest illusion. I have already spoken of the unanimous
testimony which all who have made quantitative studies in the
corresponding optical illusions have given in this matter of the
diminution of the illusion with the lapse of time. The judgments that