200 ANSWERS TO PRACTICAL QUESTIONS. 



49. Will the sight give us an idea of solidity ? 



(See Physiology, page 196, note.) 



50. Why can a skillful surgeon determine the condition of 

 the brain and other internal organs by examining the in- 

 terior of the eye ? 



(See Physiology, page 196, note.) 



51. Is there any truth in the idea that the image of the 

 murderer can be seen in the eye of the dead victim ? 



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 inverted. One upright figure 

 is reflected from the front of the cornea, which acts as a 

 convex mirror. The second proceeds from the front of 

 the crystalline lens, which has the same effect ; while the 

 inverted image proceeds from the posterior face of the 

 lens, which, being convex backwards, is, of course, con- 

 cave forwards, and acts as a concave mirror. HUXLEY. 

 The images formed upon the retina are as fleeting as light 

 itself, from the nature of the case, and disappear as soon 

 as the object is removed. 



