202 ADVANCED LESSONS IN PRACTICAL PHYSIOLOGY 



low. Match this color by inserting two small disks, black and yellow 

 respectively. Obtain a blue color by means of two large disks colored 

 green and yellow. Match the blue color by means of two small disks, 

 respectively blue and black. 



Use three disks colored red, green, and violet. The wave-lengths of 

 these colors should correspond as closely as possible to those of the 

 corresponding colors of the solar spectrum. Arrange the colored areas 

 in the proportion of red, 118 degrees; green, 146 degrees; and violet, 

 96 degrees. Rotate the disks until you have obtained a gray color. 

 Match this gray by means of two small disks, colored black and 

 white. 



11. Complementary Colors. Select from the series of colored disks 

 provided for this experiment one of a blue color. Determine what 

 color, when mixed with this blue in definite proportion, will turn it 

 gray or nearly white. The color-mixer should make from 40 to 50 

 revolutions in a minute. If the gray remain slightly tinged with color, 

 add a small section of a third color disk, neutralizing with green if the 

 tinge inclines toward red, and with red if the tinge exhibits a greenish 

 hue. Determine in the same manner the colors complementary to red, 

 yellow, orange, and green. 



12. Intensity of Light and Quality of Color (Purkinje's Phenom- 

 enon). Take two small squares of red and blue paper respectively, 

 which in a moderately bright light possess nearly the same intensity 

 of color. Observe them again in a partially darkened room. Which 

 color appears to be the brighter? 



13. Color-blindness. Place Holmgren's worsteds upon a well lighted 

 sheet of white paper. Employ as a test color light green, i. e., a mixture 

 of white and pure green, and ask the subject to soject from a lot of skeins 

 all those which appear to him to be of this light green color. If he 

 choose one or more "confusion-colors" in this case pink or yellow- 

 he should be given a skein of a pale rose color, and be asked to pick out 

 all the skeins which he thinks would match it. If the subject be red- 

 blind, he will select blue and violet; if green-blind, gray and green. 



Ask the subject to match a bright red skein. If red-blind, he will 

 choose green and brown ; if green-blind, red and light brown. 



14. Contrast. Of two equally large strips of gray paper, place one 

 upon a sheet of white paper, and the other upon a sheet of black. Which 

 strip appears to be the brighter ? 



Place these sheets close together, each sheet bearing its gray slip. 

 Gaze at both slips for twenty seconds, and .then shut the eyes. Which 

 after-image seems the brighter? 



Place a cross of gray paper in the middle of a large sheet of green 

 paper and cover both cross and background with tissue paper. Note 

 the color now imparted by the cross. Place the gray cross upon a red 

 background instead of a green. Cover the whole with tissue paper as 

 before and note the color of the cross. 



Place a strip of gray paper across the junction of a red and a green 



