37 



V. What Change takes place in the Eye in Near Vision ? 



METHOD. Repeat the experiment on the refracting sur- 

 faces of the eye (p. 35, II.), when the observed eye is looking 

 at a distant and at a near object. 



Examine again, using a Phacoscope as demonstrated. 



Make a diagram of the results arrived at. 



II. Action of the Retina and Brain. 

 I. Are Visual Sensations produced by Light only ? 



Press upon the eye-ball far back, and note the effect of 

 such mechanical pressure on the retina. 



II. Is the whole Retina stimulated by Light? 



METHODS. 1. Mariotte's Experiment. Make two marks 

 horizontal!} 7 about 4 inches apart upon a piece of plain paper. 



With the left eye closed, fix the right eye on the left-hand 

 mark with the head about 18 inches from the paper. 



Are both marks visible ? Does any change take place as 

 the paper is gradually brought towards the face ? 



Make a diagram of the results of the experiment. 



2. Make a mark on the left side of a piece of plain paper. 

 Holding the head firmly fixed at about a foot from the paper 

 and closing the left eye, keep the right eye fixed upon the 

 mark, and move the point of a pencil, held nearly horizontally, 

 slowly towards the right side of the paper. Note any change 

 in the appearance of the point of the pencil you may observe. 



Make a diagram of the experiment. CONCLUSIONS ? 



3. Map out the blind spot by moving the point of the pencil 

 from the part of the paper where it is invisible to where it 

 becomes visible. Mark the limits of the invisible area in all 

 directions from its centre. 



m. What Layer of the Retina is acted upon by Light ? 



METHOD. Purkinje's Images. In a dark room stand side 

 on against a uniformly coloured wall, with the eyes turned 

 towards the wall. By means of a lens another student 



