Photophobia
a dread or intolerance of light; a symptom more or less present in all inflammations of the eye. from the prints after they have been It is also met with in many diseases of toned and fixed because otherwise the photographs become ultimately discolored. The papers known as aristotype, argentotype, and celerotype are gelatine emulsions of chloride of silver spread on paper.
Platinum Process. An image can be obtained in platinum black if the paper is sensitized with ferric-oxalate with which is mixed a solution of chloro-platinite of potassium. The action of light on this paper reduces the ferric salt to the ferrous state, and when the ferrous salt is in solution the platinous salt is reduced by it. By floating the exposed paper on a solution of neutral potassium oxalate, which is a solvent of the ferrous oxalate, the platinum salt in contact with it is immediately reduced to the metallic state, and an image is thus built up. To fix the prints they are immersed in dilute hydrochloric acid, which dissolves away the ferric oxalate, and the oxalate of lime.
Ferroprussiate Process. - The ordinary method of making blue prints.
Composite photography, a method of superposing several or many photographs, thus getting a sort of average of the whole and showing the type. If it is a human composite photograph type, then the eyes of each sitter are brought to the same place on the lens, and the exposure for each is very short.
The most important advance in photography in recent years has been made in the direction of taking photograph natural colors. Many scientists have phs in worked on the problem and several processes have been developed. The most remarkable of these was perfected in 1907 by Antoine Lumière and his sons August and Louis, of Paris, who succeeded in taking color photographs on a single plate and in an ordinary camera, with exposures of one second and less.
Their process consists in the formation of a color screen on a glass plate by placing on it a layer of microscopic grains of transparent potato starch, in three portions colored respectively orange, green, and violet; the plate is then sensitized by the nervous system and in many febrile conditions. luminous envelope believed to completely