58 FIRST YEAR SCIENCE 



luminous body and thus appear themselves to be furnish- 

 ing light. 



An example of this is often seen about sundown when 

 the sunlight is reflected from the windows of a house, mak- 

 ing them look as if there were a source of light behind 

 them. Any dark body whose surface reflects light appears 

 itself to be luminous as long as the source of light remains, 

 but grows dark again when the source is removed. This 

 is the case of the moon. At new moon, the moon is so 

 situated with respect to the sun, that light is not reflected 

 to the earth and we cannot see it. At full moon, half 

 of the moon's entire surface reflects the sunlight, and 

 it appears very bright. 



30. Direction of Light Movement. Experiment 28. Point 

 the pinhole end of a camera obscura or pinhole camera (this consists 



of two telescoping boxes, the larger 

 having a pinhole at the end and the 

 smaller a ground glass plate) at some 

 object and move the ground glass plate 

 back and forth until a sharp image of 

 pi 32 the object is formed. Sketch on a piece 



of paper the object and the image, 



showing the direction in which you think the rays of light must 

 have traveled through the pinhole to form the image. 



A photographic camera is constructed in the same way as this little 

 camera, only a lens is placed behind the pinhole to intensify the 

 image, and it is possible to exchange the ground glass plate for a 

 photographic plate. 



There are certain properties of light which seem readily 

 apparent from our daily experiences. We cannot see 

 objects in the dark, but if a light is brought into the room 

 so that it can shine upon them, they become visible. We 

 see them because the light is reflected to us from. .them. 

 All objects except self-luminous bodies are seen by re- 

 fleeted light. 



