Photography

Photography has been called the art of fixing a shadow. The ancient Greeks knew that a clear (though upside down) image of the outside world will be projected if one makes a tiny hole in the wall of a dark room. But no one knew how to make this image permanent. Called a camera obscura, such rooms were chiefly used as aids to drawing, and understanding perspective. After the Renaissance, when perspective became important, camera obscuras become smaller and more sophisticated. By the late eighteenth century, devices had been created that used a series of telescoping boxes and a lens to focus an image. Some even used a mirror to reflect the image upwards onto a piece of glass, making tracing images easier. Gentlemen brought small, portable camera obscuras with them when they traveled, tracing the images onto a piece of paper as a way to record their journeys. In today's terms, by 1800 the camera had long since been invented, but no one had created film for it.

Many people were thinking about this problem, however. Some chemists had noticed that sunlight cased certain mixtures of silver nitrates to darken. By the early nineteenth century, inventors were trying to combine the camera with these chemical discoveries. The main problems included exposure times as long as eight hours, and how to make photographic images permanent. If light created photographic images, how could they be kept from further darkening once they were finished? This problem was eventually solved by using hyposulfite of soda (now called sodium thiosulfite) to remove the undarkened silver particles.