40 



3. What is the Effect of prolonged Stimulation of the Eye with 

 any one Part of the Spectrum ? 



METHOD. Put a disc of red paper upon a white ground in 

 a strong light. Look steadily at it for half a minute, then 

 remove it and continue to look at the white surface, and 

 note what happens. Repeat this with discs of different 

 colours. 



The colour which appears is said to be complementary to 

 the first. 



4. What is the Effect of combining these Complementary 

 Colours? 



METHOD. On a black surface place two discs of comple- 

 mentary colours. Between them place vertically a sheet of 

 glass. Now tilt the glass towards one of the discs, and on 

 looking through it the image of the disc is thrown on the 

 other disc. Note the colour change produced. 



5. Is the Power of appreciating Colour equal all over the Retina ? 



Study the result recorded on p. 39, B, and draw your con- 

 clusions. 

 

 6. Can all Individuals distinguish Colours equally well? 



METHODS. Take a set of Holmgren's wools. Give a student 

 a red wool and let him pick out all that are of the same 

 sort of colour. Find if any member of the class is colour 

 blind. 



VII. Effects of Strong or Prolonged Stimulation ? 



METHODS. (a) After keeping the eyes closed for two 

 minutes look steadily at a white mark on a black surface for 

 a few seconds and then close the eyes. 



Describe the image that appears and also any change in 

 its intensity as time passes Positive After Image. 



(6) Look steadily at the same mark for three minutes and 

 then close the eyes. 



