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.
&fist; 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.
