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HAND-BOOK OF PHYSIOLOGY. 



approaches the first. If the eye be now adjusted for a far point, the 

 second image enlarges again, becomes less distinct, and recedes from the 

 first. In both cases alike the first and third images remain unaltered in 

 size and relative position. This proves that during accommodation for 



FIG. 376. Phakoscope of Helmholtz. At B B' are two prisms, by which the light of a candle is 

 concentrated on the eye of the person experimented with at C; A is the aperture for the eye of the 

 observer. The observer notices three double images, as in Fig. 375, reflected from the eye under ex- 

 amination when the eye is fixed upon a distant object : the position of the images having been 

 noticed, the eye is then made to focus a near object, such as a needle pushed up by C; the images 

 from the anterior surface of the lens will be observed to move toward each other, in consequence of 

 the lens becoming more convex. 



near objects the curvature of the cornea, and of the posterior of the lens, 

 remains unaltered, while the anterior surface of the lens becomes more 

 convex and approaches the cornea. 



FIG. 377. Diagram representing by dotted lines the alteration in the shape of the lens, on accom- 

 modation for near objects. (E. Landolt.) 



Mechanism of Accommodation. Of course Jie lens has no in- 

 herent power of contraction, and therefore its changes of outline must be 



