478 THE OUTGO OF ENEKGY 



behind the pupil, and therefore is not much dis- 

 placed towards the pupil and the corneal image 

 upon slight movements of the light or the ob- 

 server's eye. 



Let the subject accommodate for the near point. 



The image from the anterior surface of the 

 lens will become considerably smaller, and usually 

 it will approach the middle of the pupil. The 

 image formed by a convex mirror becomes smaller 

 the smaller the radius. Hence in accommoda- 

 tion the anterior surface of the lens becomes 

 more convex. 1 



The image from the posterior surface also 

 becomes smaller, but the change is too slight 

 to be observed by the method employed in this 

 experiment. Some diminution in size would be 

 expected from the shifting of the cardinal points 

 in accommodation. Exact measurements with 

 the ophthalmometer show that the change is too 

 great to be explained in this way. 

 ; (Thus in accommodation the focal distance of 

 the lens is shortened and its principal points 

 move forwards. 



1 If in accommodation the anterior surface approached the 

 cornea, the image would become smaller through refraction in 

 the cornea, even though the anterior surface did not become more 

 convex. Calculation shows that the change thus produced is 

 very small relative to that actually observed in the above 

 experiment. 



