the static sense.

The special problem with which we are here concerned relates to the
group of factors upon which depends one's judgment that any specified
object within the visual field lies within the horizontal plane of the
eyes, or above or below that plane, and the several functions and
values of these components. The method of procedure has been suggested
by the results of preceding investigations in this general field.

The first aim of the experiments was to separate the factors of
resident and transient sensation, and to determine the part played by
the presence of a diversified visual field. To do so it was necessary
to ascertain, for each member of the experimental group, the location
of the subjective visual horizon, and the range of uncertainty in the
observer's location of points within that plane. Twelve observers in
all took part in the investigation. In the first set of experiments no
attempt was made to change the ordinary surroundings of the observer,
except in a single point, namely, the provision that there should be
no extended object within range of the subject's vision having
horizontal lines on a level with his eyes.

The arrangements for experimentation were as follows: A black wooden
screen, six inches wide and seven feet high, was mounted between two
vertical standards at right angles to the axis of vision of the
observer. Vertically along the center of this screen and over pulleys
at its top and bottom passed a silk cord carrying a disc of white
cardboard, 1 cm. in diameter, which rested against the black surface
of the screen. From the double pulley at the bottom of the frame the
two ends of the cord passed outward to the observer, who, by pulling
one or the other, could adjust the disc to any desired position. On