A YEAE IN SCIENCE 137 



distance from the eye does it become indistinct, or 

 fringed with a haze? 



Hold a book with the edge placed directly toward 

 you. Close the left eye and look at the book. Then 

 close the right eye and look at it again. Then look 

 at it with both eyes open. What differences do you 

 note ? How do you account for these differences ? 



In front of a lens, both of whose faces are convex, 

 place a lighted candle or a gas flame. Back of the 

 lens place a piece of paper to form a screen. Move 

 the paper back and forth until a distinct image of the 

 flame is seen upon the paper. What effect does it 

 have upon the image formed to move the flame nearer, 

 or farther away from the lens? 



Adjust the apparatus again so that a distinct image 

 is formed on the screen. Remove the lens and put 

 in its place one which is more convex. Which way 

 must the screen be moved to secure a distinct image? 

 Repeat this experiment, using a lens which is less con- 

 vex than the first one used; also use one which is 

 concave. 



Exercise 92. Organ of Hearing. 

 Object: A study of the ear. 



Apparatus 



Model of the ear 



Directions: The ear is made up of an external ear, 

 a middle ear, and an inner ear. On the model examine 

 the external ear. Note the pinna, the oval, expanded, 



