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 headache from reading, farsightedness is indicated. If the subject cannot read up to the twenty-foot line, nearsightedness or astigmatism is indicated. 12. _Hearing._ By consultation with the teacher of physics, plan an experiment to show that the pitch of tones depends on vibration frequency. Such an experiment can be very simply performed by rotating a wheel having spokes. Hold a light stick against the spokes so that it strikes each spoke. If the wheel is rotated so as to give twenty or thirty strokes a second, a very low tone will be heard. By rotating the wheel faster you get a higher tone. Other similar experiments can be performed. 13. Acuity of hearing can be tested by finding the distance at which the various members of the class can hear a watch-tick. The teacher can plan an experiment using whispering instead of the watch-tick. (See the author's _Examination of School Children_.) 14. By using the point of a nail, one can find the "cold spots" on the skin. Warm the nail to about 40 degrees Centigrade and you can find the "warm spots."