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Foucault's telescope. Engraving of the largest telescope used by French astronomer and physicist, Jean Bernard Leon Foucault (1819-68). He invented a way of making lenses for reflecting telescopes by chemically depositing silver onto glass in 1858. This telescope had a 80-centimetre coated glass disk and was used from the late 1850s. It was used in Paris, Lyons and (from 1864) Marseilles.
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