shorter standard, and it was not deemed advisable to keep the
subject's attention on the strain for a longer interval, since 5.0
sec. satisfied all the requirements of the experiment.

In all work here reported, the cork tip on the tapping instrument was
circular in form, and 1 mm. in diameter. In all, except one experiment
of the second group, the areas stimulated were on the backs of the
fingers, just above the nails. In the one exception a spot on the
forearm was used in conjunction with the middle finger.

In Groups 1 and 2 the intensity of stroke used was just sufficient to
give a sharp and distinct stimulation. The intensity of the
stimulation was not of a high degree of constancy from day to day, on
account of variations in the electric contacts, but within each test
of three stimulations the intensity was constant enough.

In experiments under Group 3 two intensities of strokes were employed,
one somewhat stronger than the stroke employed in the other
experiments, and one somewhat weaker--just strong enough to be
perceived easily. The introduction of the two into the same test was
effected by the use of an auxiliary loop in the circuit, containing a
rheostat, so that the depression of the first key completed the
circuit as usual, or the second key completed it through the rheostat.

At each test the subject was warned to prepare for the first
stimulation by a signal preceding it at an exact interval. In
experiments with the pendulum apparatus the signal was the spoken word
'now,' and the preparatory interval one second. Later, experiments
were undertaken with preparatory intervals of one second and 1-4/5
seconds, to find if the estimation differed perceptibly in one case