Foucault telescope. Foucault telescope, invented in the late 1850s by French physicist Leon Foucault (1819-1868) in collaboration with Swiss-born instrument-maker Marc Secretan (1804-1867, name at lower centre). The design was a silvered-glass reflecting telescope. This illustration is from 'Physique Populaire' (Emile Desbeaux, 1891).
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