. Do the after-images mix with the colors of the papers?

5. An interesting experiment with positive after-images can be performed
as follows: Shut yourself in a dark closet for fifteen or twenty minutes
to remove all trace of stimulation of the retina. With the eyes covered
with several folds of thick black cloth go to a window, uncover the eyes
and take a momentary look at the landscape, immediately covering the
eyes again. The landscape will appear as a positive after-image, with
the positive colors and lights and shades. The experiment is best
performed on a bright day.

6. _Adaptation._ Put on colored glasses or hold before the eyes a large
piece of colored glass. Note that at first everything takes on the color
of the glass. What change comes over objects after the glasses have been
worn for fifteen or twenty minutes? Describe your experience after
removing the glasses. Plan and perform other experiments showing
adaptation. For illustration, go from a very bright room into a dark
room. Go from a very dark room to a light one. Describe your experience.

7. _Contrast._ Take a medium gray paper and lay it on white and various
shades of gray and black paper. Describe and explain what you find.

8. _Color Contrast._ Darken a room by covering all the windows except
one window pane. Cover it with cardboard. In the cardboard cut two
windows six inches long and one inch wide. Over one window put colored
glass or any other colored material through which some light will pass.
By holding up a pencil you can cast two shadows on a piece of paper.
What color are the shadows? One is a contrast color induced by the
other; which one? Explain the results.

9. Make a study of the way in which women dress. What do you learn about
color effects?

10. From the Stoelting Company you can obtain the Holmgren worsteds for
studying color blindness.

11. _Defective Vision._ Procure a Snellen's test chart and determine the
visual acuity of the members of the class. Seat the subject twenty feet
from the chart, which should be placed in a good light. While testing
one eye, cover the other with a piece of cardboard. Above each row of
letters on the chart is a number which indicates the distance at which
it can be read by a normal eye. If the subject can read only the
thirty-foot line, his vision is said to be 20/30; if only the forty-foot
line, the vision is 20/40. If the subject can read above the twenty-foot
line and complains of headach