142 HOW WE USE LIGHT 



glass is called a (4) body because some light can get through 



it. (5) bodies give out (6) of their own but most bodies 



are seen by (7) light. When a smooth body reflects light, the 



angle of (8) (9) the (10) of incidence. The (11) 



in a mirror is always the (12) distance (13) of the mirror 



as the object is in (14) of the mirror. Rough surfaces give a 



soft (15) light, while (16) surfaces tend to produce a glare 



if looked at from some (17) (18) mirrors can produce a 



real image. The slowing up of light after it passes into a more 

 dense medium may cause it to (19) in a process called (20) 



STORY TEST 



MORRIS HAS SOME PRACTICAL EXPERIENCES WITH LIGHT 

 Read carefully and critically. List all the errors and suggest corrections. 



Last night about an hour before sunset I looked across a vacant 

 lot to a greenhouse. At first I thought the place was on fire 

 because there was such a glare of light. I decided however that 

 I was seeing an image of the sun in each of the glass panes. Com- 

 ing at the angle that it did, all the light was reflected and the glass 

 acted like mirrors. After the sun had gone down, thunder clouds 

 quickly shut off the twilight and it became very dark outside. 1 

 turned on the lights in the room. I turned to the window and 

 looked in the direction of the greenhouse. I saw only objects that 

 were in the room around me. The glass that had been trans- 

 parent in the daylight had become opaque in the night and now 

 acted as a perfect mirror. Out of doors everything was dark 

 because it was in the shadow cast by the earth. A flash of light 

 from my aquarium called my attention to my one gold fish I had 

 put in the water a week before. As I neared the tank, I could 

 see through the top surface and through one side. Imagine my 

 surprise to see two gold fish, and stranger still, every time one 

 moved the other one moved. I then looked straight down through 

 the top surface but could find only one fish. I decided the optical 

 illusion had been caused by the reflection of the fish by the surface 

 of the water. So I had seen the real fish and his image in a mirror. 



PROBLEM III. HOW ARE PHOTOGRAPHS MADE? 



Have you ever seen among your family heirlooms a 

 daguerreotype : an old-fashioned picture on a piece of tin 

 set in a gilded frame? This old-type picture was the 



