In the 1830s, Louis Daguerre was struggling to develop a practical method for creating permanent images when he stored chemically treated plates in a cabinet with mercury vapor from a broken thermometer. Upon retrieving the plates, he was astonished to find fully developed images. This fortunate accident led to the daguerreotype—the first practical photographic process—and revolutionized how humans document reality. Ezra Wade examines how this broken thermometer transformed visual culture, democratized portraiture, and created new ways of understanding history, science, and ourselves through the power of photographic evidence.

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