What followed was one of the most extraordinary cases of the hummingbird effect in modern history. Gutenberg made printed books relatively cheap and portable, which triggered a rise in literacy, which exposed a flaw in the visual acuity of a sizable part of the population, which then created a new market for the manufacture of spectacles. Within a hundred years of Gutenberg’s invention, thousands of spectacle makers around Europe were thriving, and glasses became the first piece of advanced technology—since the invention of clothing in Neolithic times—that ordinary people would regularly wear
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