[5] Münsterberg, H.: 'Beiträge zur Exper. Psy.,' Freiburg i.B.,
1889, Heft II., S. 171.

Now, in my experiments, I endeavored to guard against all of these
objections. In the first place, I made a far greater number of tests.
Then my apparatus enabled me, firstly, to use a very wide range of
distances. Where the points are set in a solid block, the experiments
with long distances are practically impossible. Secondly, the
apparatus enabled me to control accurately the pressure of each point.
Thirdly, the contacts could be made simultaneously or successively
with much precision. This apparatus (Fig. 1) was planned and made in
the Harvard Laboratory, and was employed not only in our study of this
particular illusion, but also for the investigation of a number of
allied problems.

[Illustration: FIG. 1.]

Two æsthesiometers, A and B, were arranged in a framework, so that
uniform stimulations could be given on both arms. The æsthesiometers
were raised or lowered by means of the crank, C, and the cams, D and
E. The contacts were made either simultaneously or successively, with
any interval between them according to the position of the cams on the
crank. The height of the æsthesiometer could be conveniently adjusted
by the pins F and H. The shape of the cams was such that the descent
of the æsthesiometer was as uniform as the ascent, so that the
contacts were not made by a drop motion unless that was desired. The
sliding rules, of which there were several forms and lengths, could be
easily detached from the upright rods at _K_ and _L_. Each of the
points by which the contacts were made moved easily along the sliding