because of its length, has already, as it were, left the specious
present, and has suffered the foreshortening effect of being relegated
to the past. And, on the other hand, after the short distance of the
open space has been traversed the sensations of muscular strain become
very pronounced, and cause a premature judgment of equality.

One subject, who was very accurate in his judgments, and for whom the
illusion hardly existed, said, when asked to explain his method of
judging, that after leaving the filled space he exerted a little more
pressure with his finger as he passed over the open space, so as to
get the same quantity of tactual sensations in both instances. The
muscular tension that was set up when the subject had passed out over
the open space a short way was very plainly noticeable in some
subjects, who were seen at this time to hold their breath.

I have thus far continually spoken of the space containing the tacks
as being the filled space, and the smooth surface as the open space.
But now we see that in reality the name should be reversed, especially
for the longer distances. The smooth surface is, after the first few
centimeters, very emphatically filled with sensations arising from the
organism which, as I have already intimated, are of the most vital
importance in our spatial judgments. Now, according to the most
generally accepted psychological theories, it is these organic
sensations which are the means whereby we measure time, and our
spatial judgments are, in the last analysis, I will not for the
present say dependent on, but at any rate fundamentally related to our
time judgments.


VIII.