e strange if its
mobility did not show itself in the motor reaction. It does in fact
show itself in the _sense organ adjustments_ which amount to
exploratory reactions. Attention to an object in the hand is shown by
"feeling of it", to a substance in the mouth by tasting movements, to
an odor by sniffing movements, to a sound by cocking the head and
turning the eyes towards the source of sound. The most instructive of
this type of attention-reactions are those of the eyes. The eye is
focused on the object that arouses attention, the lens being
accommodated for its distance by the action of the little ciliary
muscle inside the {250} eyeball; the two eyes are converged upon the
object, so that the light from it strikes the fovea or best part of
each retina; and the eyes are also turned up, down or sidewise, so as,
again, to receive the light from the object upon the fovea.

This last class of eye movements is specially instructive and shows
specially well the mobility of attention. Let a bright or moving
object appear somewhere in the field of view--immediately the eyes
turn towards it with a quick jump, fixate it for a few seconds and
then jump elsewhere unless the object is found to be specially
significant. Watch the eyes of one who is looking at a picture or
scene of any sort, and you will see his eyes jumping hither and
thither, as his attention shifts from one part of the scene to
another. Ask him to abstain from this jumpy movement and let his eyes
"sweep over" the scene, and he will confidently try to follow your
instructions, but if you watch his eyes you will find them still
jumping. In fact, "sweeping the glance" is a myth. It cannot be done.
At least, there is only one case in which it can be done, and that is
when there is a moving object to look at. Given an object moving at a
moderate speed across the field of view, and the eyes can follow it
and keep pace with it pretty accurately. But without the moving object
as stimulus, the eyes can only execute the jump movement. There are
thus two types of exploratory eye movement: the "jump" in passing from
one object to another, and the "pursuit movement" in examining a
moving object.

In reading, the eye moves by a series of short jumps from left to
right along the first line of print, makes a long jump back to the
beginning of the second line and another series of short jumps along
that line, and so on. To appreciate the value of this jerky movement,
we need t