454 THE OUTGO OF ENERGY 



tern B into two parts, proportional to the anterior 

 focal distance of the cornea (23.266 mm.) and the 

 focal distance of the lens (50.617 mm.). As K l A 

 lies 7.829 mm. and K^ B 5.726 mm. behind the cor- 

 nea, the distance between them is 2.103 mm. This 

 is to be divided in the proportion 23.266 : 50. 617. 

 23.266 + 50.617 : 50.617 : : 2.103 :x. x= 1.4408. 

 Thus o lies 1.4408 mm. behind the first principal 

 point of the crystalline lens (System B) and 

 consequently 



5.726 4- 1.4408 = 7.167 mm. 

 behind the cornea. 



By formula (3 b), K\ C, the first nodal point or 

 the image of o formed by the cornea, is found to be 



23.266 X 7.167 



Q1 nnc . = 6.97 mm. behind the cornea. 



ol.uyo /.lo/ 



The second nodal point, K 2 C, or image formed 



. , 50.617 X 1.4408 



of o by the crystalline lens, is 5Q 617 _ L4408 



= 1.401 mm. behind the second principal point 

 of the crystalline lens, and consequently 5.924 

 + 1.401 = 7.33 mm. behind the cornea. 



The distance K\K* between the first and 

 second nodal points of System C is 7.33 

 6.97 = 0.36 mm. The distance Hi H 2 = K^ K 2 . 



Principal Foci. Kays falling on the cornea par- 

 allel to the principal axis are refracted by hi A and 



