Johann Heinrich Schulze. 1687-1744. Schulze was a German Professor at the University of Altdorf, whose experiments paved the way towards photography. Though it was known that certain chemicals darken when exposed to the sun, it was not clear whether it was the action of light or heat which had this effect. In 1727 Schulze heated some silver nitrate in an oven, and discovering that it did not darken was able to eliminate heat as the darkening agent. Having noticed that a glass jar containing a particular chemical mixture changed colour on one side - that facing the window, he applied paper stencils to a bottle containing silver nitrate and chalk, discovering that where the substance was not exposed to light it remained white. He published details of his investigations, but these did not become popular until after he had died.

Johann Heinrich Schulze. 1687-1744. Schulze was a German Professor at the University of Altdorf, whose experiments paved the way towards photography. Though it was known that certain chemicals darken when exposed to the sun, it was not clear whether it was the action of light or heat which had this effect. In 1727 Schulze heated some silver nitrate in an oven, and discovering that it did not darken was able to eliminate heat as the darkening agent. Having noticed that a glass jar containing a particular chemical mixture changed colour on one side - that facing the window, he applied paper stencils to a bottle containing silver nitrate and chalk, discovering that where the substance was not exposed to light it remained white. He published details of his investigations, but these did not become popular until after he had died.

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38.0 x 46.7 cm | 15.0 x 18.4 in (300 dpi)