ooking
rigidly straight ahead, take a bit of color in the hand and bring
it slowly in from the side, noticing what color sensation you get
from it when it can first be seen at all, and what changes in color
appear as it moves from the extreme periphery to the center of the
field of view, (b) Form sense. Use printed letters in the same way,
noticing how far out they can be read, (c) Sense of motion. Notice
how far out a little movement of the finger can be seen. Sum up
what you have learned of the differences between central and
peripheral vision. What is the use of peripheral vision?

10. Light and dark adaptation. Go from a dimly lighted place
into bright sunlight, and immediately try for an instant to read
with the sun shining directly upon the page. Remaining in the
sunlight, {242} repeat the attempt every 10 seconds, and notice
how long it takes for the eye to become adapted to the bright
light. Having become light-adapted, go back into a dimly lighted
room, and see whether dark-adaptation takes more or less time than
light-adaptation.

11. Color adaptation. Look steadily at a colored surface, and notice
whether the color fades as the exposure continues. Try looking at
the color with one eye only, and after a minute look at the color
with each eye separately, and notice whether the saturation
appears the same to the eye that has been exposed to the color,
and to the eye that has been shielded.

12. Negative after-images. Look steadily for half a minute at a
black cross upon a white surface, and then turn the eyes upon a
plain gray surface, and describe what you see. (b) Look steadily
for half a minute at a colored spot upon a white or gray
background, and then turn the eyes upon a gray background, and
note the color of the after-image of the spot. Repeat with a
different color, and try to reach a general statement as to the
color of the negative after-image.

13. Positive visual after-images. Look in the direction of a bright
light, such as an electric light, holding the hand as a screen
before the eyes, so that you do not see the light. Withdraw the
hand for a second, exposing the eyes to the light, and immediately
screen the eyes again, and notice whether the sensation of the
light outlasts the stimulus.

14. Tactile after-images. Touch the skin lightly for an instant,
and notice wh