between two collinear open
spaces for the particular region of the skin tested. Three points were
taken in a line, and one of the end points was moved until the two
adjacent open spaces were pronounced equal. Then one of the spaces was
filled, and the process of finding another open space equivalent to
this filled space was repeated as before. This finding of two
equivalent open spaces was repeated at frequent intervals. It was
found unsafe to determine an equivalent at the beginning of each
sitting to be used throughout the hour.

Two sets of experiments were made with the illusion in this form. In
one the contacts were made simultaneously; the results of this series
are given in Table I. In the second set of experiments the central
point which divided the open from the filled space touched the skin
first, and then the others in various orders. The object of this was
to prevent fusion of the points, and, therefore, to enable the subject
to pronounce his judgments more rapidly and confidently. A record of
these judgments is given in Table II. In both of these series the
filled space was always taken near the wrist and the open space in a
straight line toward the elbow, on the volar side of the arm. At
present, I shall not undertake to give a complete interpretation of
the results of these two tables, but simply call attention to two
manifest tendencies in the figures. First, it will be seen that the
short filled distance of four centimeters is underestimated, but that
the long filled distance is overestimated. Second, in Table II., which
represents the judgments when the contacts were made successively, the
tendency to underestimate the short distance is less, and at the same
time we notice a more pronounced overestimation of the longer filled
distances. I shall give a further explanation of these results in
connection with later tables.

TABLE I.

4 cm. 6 cm. 8 cm.
Filled. Open. Filled. Open. Filled. Open.

F. 5.3 4.7 7.8 7.6 9.3 10.5
F. 5.7 4.4 6.5 7.3 9.2 11.7
F. 6.0 5.6 8.2 7.3 8.7 10.8
--- --- --- --- --- ----
Av. 5.7 4.9 7.5 7.4 9.1 11.0

R. 5.7 5.1 6.7 6.8 9.3 10.2
R. 5.4 5.4 7.2 7.1 8.5 10.7
R. 4.6 4.2