226 



EXPERIMENTAL PHYSIOLOGY 



is then moved into a fresh meridian and a fresh observation taken, and so 

 on until a series of points have been mapped out upon the chart which lie 

 on the limit of distinct vision. These are united by a curved line, such as the 

 dotted line in fig. 177, which represents the normal average field of vision for 

 white light for the right eye. 



Having determined this for a white object, next determine similar lines 

 for coloured objects. 



For the white object it is seen that the field of vision extends more 



100 



100 



180 

 Fig. 177. — A Perimetric Chart for the Right Eye. (Hallirurton.) 



to the outer than to the inner side, and further above than below the 

 horizontal meridian. 



In the case of colours it will be found that the capacity for distin- 

 guishing them diminishes more rapidly at the periphery than is the 

 case for white light. 



The field of vision is more extensive for blue than for other 

 colours ; it is least extensive for green and intermediate for red. 



