series the open spaces were presented first. In the previous
experiments, so far as I have reported them, the filled spaces were
always presented first.

[Illustration: FIG. 10.]

In order to enable the subject to make proper connections with the
first point in the filled space, when the open space was presented
first, a slight depression was put in the smooth surface. This
depression amounted merely to the suggestion of a groove, but it
sufficed to guide the finger.

The general results of the first series of experiments with this
apparatus were similar to those already given, but were based on a
very much larger number of judgments. They show at once that the short
filled spaces are overestimated, while the longer spaces are
underestimated. The uniformity of this law has seemed to me one of the
most significant results of this entire investigation. In the results
already reported from the experiments with the former apparatus, I
have mentioned the fact that the judgments upon the distances
fluctuate more widely when one is filled and the other open, than when
both are open. This fluctuation appeared again in a pronounced way in
the present experiments. I now set about to discover the cause of this
variation, which was so evidently outside of the limits of Weber's
law.


TABLE XI.

I. II.