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OUR PHYSICAL WORLD 



tracing paper is illuminated but shows no distinct picture of 

 objects. 



If, in place of the tracing paper, a photographic plate is 

 set so as to cover the opening opposite the pinhole with its 

 sensitive or film side which is the dull side toward the hole, you 

 can take a picture with this camera. You must take the plate out 

 of the box or package in which you buy it, in a room that is 

 entirely dark except for the photographer's lamp used to give you 

 light (see " darkroom " below), and fasten it in place. Cover that 

 end of the box and the plate with the dark cloth and keep your 

 finger over the pinhole until the camera is in position on the 



FIG. 132. The pinhole camera 



window sill. Then uncover the hole for three or four minutes 

 if the sun is shining and it is the middle of the day, much longer 

 if the day is cloudy. The plate must then be developed to 

 bring out the picture (see below). 



A modification of the pinhole camera is used in sketching 

 objects or in mapping landscapes. The device is known as a 

 camera obscura. Take a good-sized wooden box that is light- 

 tight and large enough to receive your head and shoulders. 

 Remove the top of it. Paint or stain the inside dull black. In 

 the middle of one side, 6 inches from one end, bore a small 

 hole with a drill. At the middle of the end adjacent to the 

 hole set a 6-inch post at right angles to the end. Mount on this 

 a plane mirror facing the drill hole and inclined 45 to the post 



