WHAT IS COLOR? 163 



Paste cardboard strips on the inside of cover to hold the sensitized 

 plate. 



The picture is made on a glass plate which is held in place by 

 narrow strips of cardboard glued in along the vertical edges of the 

 plate. This plate is to be put into the camera while in a dark room. 

 Of course, the pinhole should be kept covered until you reach the 

 object you wish to photograph and covered again after the picture is 

 taken. The exposure, depending on the light, should be from ten to 

 twenty minutes. 



REFERENCE READING 



Comptoris Pictured Encyclopedia. 



Bragg, Sir William, The Universe of Light. Macmillan, 1933. 



Dull, C. E., Modern Physics. Holt, 1929. Page 404-498. 



Houston, E. J., The Wonder Book of Light. W. and R. Chambers, Ltd. 



Luckiesh, M., Artificial Light. Century, 1920. 



Meister, M., Energy and Power. Scribner's, 1930. 



Whitman, W. G., Household Physics. Wiley and Sons, 1932. Prin- 

 ciples of Light, pages 272-290 ; Natural Light, pages 292-308 ; Arti- 

 ficial Light, pages 310-321 ; Illumination, pages 322-342. 



structor who has a micrometer caliper, with which to measure the needle 

 so you can make the hole just the right diameter. 



Having obtained a needle of the right diameter, do not force it all 

 at once into the tinfoil, but push it in slowly, first on the one side, and 

 then on the other so as not to tear the foil. When you have made the 

 hole, be sure to smooth off the edges, as a clear picture cannot be made 

 unless you have a clean cut hole. 



