<P> In 1614 Angelo Sala wrote in his paper Septem Planetarum terrestrium Spagirica recensio: "When you expose powdered silver nitrate to sunlight, it turns black as ink". He also noted that paper wrapped around silver nitrate for a year had turned black . </P> <P> Wilhelm Homberg described how light darkened some chemicals (photochemical effect) in 1694 . </P> <P> Around 1717 German polymath Johann Heinrich Schulze accidentally discovered that a slurry of chalk and nitric acid into which some silver particles had been dissolved was darkened by sunlight . After experiments with threads that had created lines on the bottled substance after he placed it in direct sunlight for a while, he applied stencils of words to the bottle . The stencils produced copies of the text in dark red, almost violet characters on the surface of the otherwise whitish contents . The impressions persisted until they were erased by shaking the bottle or until overall exposure to light obliterated them . Schulze named the substance "Scotophorus", when he published his findings in 1719 . He thought the discovery could be applied to detect whether metals or minerals contained any silver and hoped that further experimentation by others would lead to some other useful results . Schulze's process resembled later photogram techniques and is sometimes regarded as the very first form of photography . </P> <P> The early science fiction novel Giphantie (1760) by the French Tiphaigne de la Roche described something quite similar to (colour) photography, a process that fixes fleeting images formed by rays of light: "They coat a piece of canvas with this material, and place it in front of the object to capture . The first effect of this cloth is similar to that of a mirror, but by means of its viscous nature the prepared canvas, as is not the case with the mirror, retains a facsimile of the image . The mirror represents images faithfully, but retains none; our canvas reflects them no less faithfully, but retains them all . This impression of the image is instantaneous . The canvas is then removed and deposited in a dark place . An hour later the impression is dry, and you have a picture the more precious in that no art can imitate its truthfulness ." De la Roche thus imagined a process that made use of a special substance in combination with the qualities of a mirror, rather than the camera obscura . The hour of drying in a dark place suggests he possibly thought about the light sensitivity of the material, but he attributes the effect to its viscous nature . </P>

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