16 



PRACTICAL PHYSIOLOGY 



where is an object on the right focussed ? Is the image erect or 

 inverted ? 



2. How does the image move with movement of the object ? 



3. Can a near object and a far object be focussed at the same 

 time? 



4. What is the relationship of the size of the image to the distance 

 of the object ? 



Revise your knowledge of the optical properties of a convex lens, 

 using Kiihne's artificial eye or some substitute. 



B. Examine the image of a candle formed on an obscure glass 

 plate placed over a hole cut in the back of a fresh eye of an ox. 



2. At what Surfaces of the Eye are the Rays of Light Refracted ? 

 Note the formation of an image from each of the two refracting 



FIG. 5. Kiihne's artificial eye and accessory parts. 



surfaces of a biconvex lens due to the reflection which takes place 

 at these surfaces. Study (1) how the size of the image varies with 

 the curvature of the lens, (2) the position, erect or inverted, of the 

 image from each surface of the lens, and (3) the direction in which it 

 moves when the object is moved. 



METHOD. In a dark room hold a candle to the outer side of the 

 eye of a fellow student, and notice that three reflected images are 

 to be seen one large, clear, distinct, erect image from the anterior 

 surface of the cornea, one small, distinct, inverted image from the 

 posterior surface of the lens, and one much less distinct erect image, 

 larger than the first and apparently lying almost behind it and seen 

 best from the side away from the light, from the anterior surface 

 of the lens Sanson's Images. From the size of these images draw 



