The Blut-Fin (location of the Mire du Nord, first siting post for Picard’s measuring of the meridian across France, to begin the first accurate survey of Louis XIV’s realm) was one of thirty Montmartre windmills in 1700, milling grains, pepper, spices, locally-quarried gypsum for plaster and porcelain, crushing grapes. By 1830s most had gone, as…