these subjects, Mr. Koffka, a student of philosophy, I
carried these tests somewhat further, varying them partly by increasing
the number of sheets of paper, partly by decreasing the distance between
them. The increase in the number of sheets made only a slight difference
in the results. With 200 tests in each case I obtained the following
results:

No. of sheets : 5 6 7 8 9 10
Correct inferences: 77% 72% 72% 69% 73% 68%

With but few exceptions, the errors were, as a rule, of one place. The
series with an odd number of sheets (5, 7, 9) gave better results than
those with an even number (6, 8, 10). In the tests with the odd number
of sheets the experimenter (K.) stood in front of the middle sheet, so
that it was at the apex of a right angle made by the series of papers
and the median plane of the subject's body; whereas in the case of the
even number of papers the subject stood opposite the space between the
two middle sheets, thus making the position of the sheets less
favorable.

In the preceding tests the distance between the centers of the
neighboring sheets was always 50 centimeters, so that the angle through
which the median plane of the experimenter's body would have to turn in
order to pass from one sheet to the next, was about 3-3/4 degrees. In
the following tests these distances were gradually decreased. The
sheets, always five in number, were replaced by ever narrower white
strips of paper mounted on dark cardboard and illumined by a Nernst
lamp. The following table shows the decrease in correct inferences
running parallel with the decrease of the angle through which the
subject would have to turn in order to be in line with the several
pieces of a series successively. The percentage in each case is based
upon at least 100 tests.

Angle: 3-3/4 deg. 3 deg. 2-1/2 deg. 2 deg. 1-1/2 deg. 1 deg.
Distance between the
centres of two neighboring
papers: 50cm. 39cm. 33cm. 26cm. 20cm. 13cm.
No. of correct inferences: 77% 73% 71% 68% 66% 61%

A curious and unexpected change was here noted in the subject, Mr.
Koffka, who, while concentrating his attention to the uttermost, began
unawares to develop a new system of expressive movements of the head.
When the distance between the sheets was relatively great, he had been
in the habit of turning his head and eyes in the direction of the sheet
int