BY J. FRANKLIN MESSENGER.


The investigation which I am now reporting began as a study of the
fusion of touch sensations when more than two contacts were possible.
As the work proceeded new questions came up and the inquiry broadened
so much that it seemed more appropriate to call it a study in the
perception of number.

The experiments are intended to have reference chiefly to three
questions: the space-threshold, fusion of touch sensations, and the
perception of number. I shall deny the validity of a threshold, and
deny that there is fusion, and then offer a theory which attempts to
explain the phenomena connected with the determination of a threshold
and the problem of fusion and diffusion of touch sensations.

The first apparatus used for the research was made as follows: Two
uprights were fastened to a table. These supported a cross-bar about
ten inches from the table. To this bar was fastened a row of steel
springs which could be pressed down in the manner of piano keys. To
each of these springs was fastened a thread which held a bullet. The
bullets, which were wrapped in silk to obviate temperature sensations,
were thus suspended just above the fingers, two over each finger. Each
thread passed through a small ring which was held just a little above
the fingers. These rings could be moved in any direction to
accommodate the bullet to the position of the finger. Any number of
the bullets could be let down at once. The main object at first was to
learn something about the fusion of sensations when more than two
contacts were given.