THE NATURE OF LIGHT. 371 



even. Tack them in this position. Make thus two more similar 

 screens. The three screens, with a bit of candle three inches long, 

 placed upon one of the remaining blocks, furnishes the material 

 for the experiment above. Save the screens and three blocks for 

 future use. (See Fig. 280.) 



585. Inverted Images. If light from a highly- 

 illuminated body be admitted to a darkened room through 

 a small hole in the shutter and there received upon a white 

 screen, it will form an inverted image of the object upon 

 the screen. Every visible 

 point of the illuminated 

 object sends a ray of light 

 to the screen. Each ray 

 brings the color of the 



point which sends it and prints the color upon the screen. 

 As the rays are straight lines, they cross at the aperture; 

 hence, the inversion of the image. The image will be dis- 

 torted unless the screen be perpendicular to the rays. 

 The darkened room constitutes a camera olscura. The 

 image of the school playground at recess is very inter- 

 esting and easily produced. 



(a.) Place a lighted candle about a meter from a white screen in a 

 darkened room. (The wall of the room will answer for the screen.) 

 Pierce a large pin-hole in a card, and hold it between the flame and 

 the screen. An inverted image of the flame will be found upon the 

 screen. 



(b.) Bore an inch hole in one side of a wooden box; cover this 

 opening with tinfoil, and prick the tinfoil with a needle. Place a 

 lighted candle within the box ; close the box with a lid or a shawl, 

 and hold a paper screen before the hole in the tinfoil. Move the 

 screen backward and forward, and notice that in any position the 

 size of the object is to the size of the image as the distance from 

 the aperture to the object is to the distance from the aperture to the 

 image. 



(c.) Cover one end of a tube, 10 or 12 cm. long, with tinfoil ; the 

 other end with oiled paper, Prick a pin-hole in the tinfoil and turn 



