illusion, endeavor to explain these anomalous facts.

In section IV. I mentioned the fact that I found the illusion for
passive touch to be subject to large fluctuations. This is true also
of the illusion for active touch. When the finger-tip is drawn over
the filled, and then out over the open space, the limits between which
the stopping point varies is a much wider range than when the
finger-tip is drawn over two open spaces. In the latter case I found
the variation to follow Weber's Law in a general way. At first I
thought these erratic judgments were mere guesses on the part of the
subject; but I soon discovered a certain consistency in the midst of
these extreme fluctuations. To show what I mean, I have plotted some
diagrams based on a few of the results for three subjects. These
diagrams are found in Fig. 8. It will be observed that the curve which
represents the collection of stopping points is shorter and higher
where the judgments were on two open spaces. This shows plainly a
greater accuracy in the judgments than when the judgments were on a
filled and an open space, where the curves are seen to be longer and
flatter. This fluctuation in the illusion becomes important in the
theoretical part of my discussion, and, at the risk of apparently
emphasizing unduly an insignificant matter, I have given in Fig. 9 an
exact copy of a sheet of judgments as it came from the apparatus. This
shows plainly how the illusion wears away with practice, when one
distance is given several times in succession. The subject was allowed
to give his judgment on the same distance ten times before passing to
another. A glance at the diagram will show how pronounced the illusion
is at first, and how it then disappears, and the judgment settles down
to a uniform degree of accuracy. It will be seen that the short filled
space is at first overestimated, and then, with the succeeding
judgments, this overestimation is gradually reduced. In the case of