ACCOMMODATION. 265 



which allows only the red and violet rays to pass through it. 

 Accommodate for the violet rays or approach the light, 

 the flame appears violet, surrounded with a reddish halo; 

 on accommodating for the red, or on receding, the centre is 

 reddish with a violet halo. 



(c.) V. Bezold's Experiment. Make a series (10 to 12) of 

 concentric circles, black and white alternately, each 1 mm. 

 thick, the diameter of the whole being about 15 mm. On 

 looking at these circles when they are placed within the 

 focal distance, one sees the white become pink; to some 

 eyes it appears yellow or greenish. The same is seen on 

 looking at concentric black and white circles, or parallel 

 black and white lines from a distance outside the far point 

 of vision, the white appears red and the black bluish. 



5. Accommodation. 



(a.) Standing near a source of light, close one eye, hold 

 up both forefingers not quite in a line, keeping one finger 

 about six or seven inches from the other eye, and the other 

 forefinger about sixteen to eighteen inches from the eye. 

 Look at the near finger, a distinct image is obtained while 

 the far one is blurred or indistinct. Look at the far image, 

 it becomes distinct, while the near one becomes blurred. 

 Observe that in accommodating for the near object one is 

 conscious of a distinct effort. 



(b.) Ask some one to note the diameter of your pupil 

 when you accommodate for the near and distant object 

 respectively. In the former case the pupil contracts, in the 

 latter it dilates. Ask a person to accommodate for a distant 

 object, and look at his eye from the side and somewhat from 

 behind, the half of the pupil projects beyond the margin of 

 the cornea. When he looks at a near object in the same 

 line, and without moving the eyeball, observe that the whole 

 pupil and a part of the iris next the observer are projected 

 forwards, owing to the increased curvature of the anterior 

 surface of the lens. 



(c.) Hold a thin wooden rod or pencil about a foot from 

 the eyes, and look at a distant object. Note that the object 

 appears double. Close the right eye, the left image dis- 

 appears and vice versa. 



