410 ELEMENTARY PHYSIOLOGY less. 



the needle a distinct. He will find he can do so readily 

 enough, but that the act is accompanied by a sense of 

 effort somewhere in the eye. And in proportion as a 

 becomes distinct, b will become blurred. Nor will any 

 effort enable him to see a and b distinctly at the same 

 time. 



Multitudes of explanations have been given of this 

 remarkable power of adjustment ; but the true solution of 

 the problem has been gained bj' the accurate determina- 

 tion of the nature of the changes in the eye which 



Fio. 130. — Diagram of the Images of a Candle-Flame seen by Re- 

 flection FROM the surface OF THE CORNEA AND THE TWO SURFACES 



OF THE Lens. 



A, as seen when the ej'e is adjusted for a distant object ; B, as they 

 appear when the eye is fixed on a near object. 



accompany the act. When the flame of a taper is held 

 near, and a little on one side of, a person's eye, any one 

 looking into the eye from a proper point of view will 

 see three images of the flame, two upright and one in- 

 verted. One upright bright image is reflected from the 

 front of the cornea, which acts as a convex mirror. The 

 second, less bright, proceeds from the front of the 

 crystalline lens, which has the same effect ; while the 

 inverted image, which is small and indistinct, proceeds 



