In the Ancienne église de Saint-Martin-des-Champs at the Musée des Arts et Métiers. The circle of people below are looking at a replica of Foucault's Pendulum. The museum also has Pascal's adding machines and the standard meter bar in platinum (previously mentioned here).
Before brunch today we tracked down Les Spécialistes, a building façade installed by some conceptual artists and discussed here. Looks like someone took the doorknob.