566 



STUDIES IN ADVANCED PHYSIOLOGY. 



accuracy, been made out on the human eye and are given 

 approximately correct in Figure 178. 



It will be noticed that in the lens itself not far from its 

 posterior portion there are indicated two points marked k' 

 and k". These are called the nodal points of the eye. A 

 ray of light entering in any direction through the pupil and 

 passing through point k' will proceed from k' to k", and at 

 k" be bent parallel to its direction of entrance. As,. how- 

 ever, for practical purposes k' and k" are very close to- 

 gether we may imagine them as one point, and that any ray 

 of light which passes through k' will be continued to the 

 retina without suffering any bending 



Fig. 178. SEMI-DIAGRAMMATIC SECTION OK THE EYE-BALL. 

 The explanation of lines and letters is given in the text. 



To know, therefore, where on the retina a certain lum- 

 inous point will be imaged, it is necessary to draw a straight 



