The novel begins with the main character, Casaubon, in the Conservatoire des Arts et Metiers staring at the titular pendulum. He looks at the pendulum thinking about eternity, geometry, and a variety of other related subjects in a kind of stream of consciousness. The museum is about to close and he needs to find a hiding place so he can avoid detection by the night watch. His friend, Jacopo Belbo has apparently been taken hostage by an unknown group of people and Casaubon is supposed to meet Belbo and his captors in the museum at midnight. He rushes through the museum looking for a suitable place to hide, taking notice and reflecting on the other exhibits as he goes. Finding a periscope, Casaubon decides to take cover there and hope he can keep awake and avoid detection. (read more)