124 LIGHT 



6. What is a focus? What is the principal focus? Can 

 there be more than one focus formed through a lens? Can more 

 than one principal focus be formed ? 



7. Explain, by a diagram, how images are formed through a 

 convex lens. 



8. Briefly show how images are formed in the eye. What is the 

 cause of near sight and of far sight ? How may each be remedied ? 



9. Describe the use of the photographic camera. How is it 

 usually focused ? , 



10. What is a microscope ? How does a convex lens magnify 

 images ? What is a compound microscope ? 



1 1. State the use of a telescope. For what purpose are the larger 

 ones made ? Are spyglasses, field glasses, opera glasses, etc., micro- 

 scopes or telescopes ? 



SECTION III 

 COLOR 



145. What is Color? We are so used to thinking of 

 color as a part or property of any substance, that we 

 may at first find it hard to understand that color is a 

 property of light waves. 



Experiment 95. Examine colored pieces of paper in day- 

 light ; then in red, blue, or other colors of light. (This may be 

 done by cutting a small opening in a wooden box and putting a 

 lamp inside ; red, blue, or other colored glass may be held over 

 the opening. This should be done in a darkened room.) Now 

 look at white paper in daylight, red light, etc. Does it always 

 seem to be the same color ? Examine pieces of dark cloth (dark 

 blue, green, gray, etc.) in lamplight ; mark each, and later look 

 at them in daylight. Can you guess the color of each piece cor- 

 rectly by lamplight ? 



From these experiments we learn that the color of a 

 body seems to change when differently colored waves 



