\Pho*tog"ra*phy\, n. [Photo- + -graphy: cf. F.
photographie.]
1. The science which relates to the action of light on
   sensitive bodies in the production of pictures, the
   fixation of images, and the like.
2. The art or process of producing pictures by this action of
   light.
Note: The well-focused optical image is thrown on a surface
      of metal, glass, paper, or other suitable substance,
      coated with collodion or gelatin, and sensitized with
      the chlorides, bromides, or iodides of silver, or other
      salts sensitive to light. The exposed plate is then
      treated with reducing agents, as pyrogallic acid,
      ferrous sulphate, etc., to develop the latent image.
      The image is then fixed by washing off the excess of
      unchanged sensitive salt with sodium hyposulphite
      (thiosulphate) or other suitable reagents.