ranging from one which was on the whole distinctly perceptible as
longer than the standard to one on the whole distinctly shorter, was
represented by a series of cards. Two such series were shuffled
together, and the intervals given in the order so determined. Thus,
when the pile of cards had been gone through, two complete series had
been given, but in an order which the subject was confident was
perfectly irregular. As he also knew that in a given series there were
more than one occurrence of each compared interval (he was not
informed that there were exactly two of each), every possible
influence favored the formation each time of a perfectly fresh
judgment without reference to preceding judgments. The only fear was
lest certain sequences of compared intervals (_e.g._, a long compared
interval in one test followed by a short one in the next), might
produce unreliable results; but careful examination of the data, in
which the order of the interval was always noted, fails to show any
influence of such a factor.

To be more explicit with regard to the conditions of judgment; two
intervals were presented to the subject in immediate succession. That
is, the second stimulation marked the end of the first interval and
the beginning of the second. The first interval was always the
standard, while the second, or compared interval, varied in length, as
determined by the series of cards, and the subject was requested to
judge whether it was equal to, or longer or shorter than the standard
interval.

In all of the work under Group 1, and the first work under Group 2,
the standard interval employed was 5.0 seconds. This interval was
selected because the minimum variation possible with the pendulum
apparatus (½ sec.) was too great for the satisfactory operation of a