and delight. It became a pastime among the well-to-do 
     throughout Europe.
          By the 1600s, painters in many countries were 
     using it to solve problems of perspective. Some artists 
     found it easier to trace the two-dimensional image of the 
     camera obscura than to work from three-dimensional 
     reality.
          The next step was obvious. Could the image be 
     preserved, saving the artist even more work? The idea 
     seems to have been present for two centuries, awaiting 
     the development of chemistry—and of demand.