152 LIGHT AND SOUND 



and over this is pasted a strip of tin foil. A smooth pin- 

 hole is made in the foil. The inside of the box is black, 

 except for a white space just opposite 

 the tin foil. If the room is darkened, 

 and a small, lighted candle is placed 

 FIG 141 before the pin-hole, an image of the 



when light from an object candle is seen inside the box, on the 



passes through a pin-hole 



ima converted 1 box ' the wni ^ e screen; but the image is com- 

 pletely turned about. 



The explanation is as follows: The candle flame is sending out 

 rays of light from a large number of points on its surface. Each 

 of these points sends a small beam through the pin-hole, and 

 the beam, when it strikes the white screen, makes an image of 

 the part of the candle flame from which it came. But all the beams 

 cross at the pin-hole. Hence the light from the top of the flame will 

 form the bottom of the image, and the light from the right side will 

 form the left side of the image, and the image is completely inverted. 

 A landscape seen through a very small point is also turned about. 



169. Shadows. That light travels in straight lines is 

 shown, also, by the forming of shadows. When an opaque 

 body is put in the way of light rays, it cuts off the light 

 from the space behind it, producing a shadow. If the 

 source of light is very small 

 (S, Fig. 142), the shadow is 

 very distinct. But if the 

 luminous body has a consider- 

 able surface, and sends out FlG - 142 - 



The shadow cast by an object that is 

 light from many pOintS, the illuminated by a point of light is of 



shadow will have two parts: 



one receiving no light at all, and the other getting light 



from part of the luminous surface, but not from all of it. 



