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General View of Niagara Falls from Bridge
This Detroit Publishing Company photographic print from around 1901 shows Niagara Falls, the spectacular natural wonder on the Niagara River, which forms part of the border between Canada and the United States. The photograph is a cyanotype, a process that was invented in 1842 by the British astronomer and photography pioneer Sir John Herschel (1792-1871) and came into widespread use in the 1880s. Herschel discovered that water-soluble iron salts, when exposed to sunlight, form the compound known as Prussian Blue (a complex molecule that contains the compound cyanide, hence the ...
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Library of Congress