Gnomon of Saint-Sulpice

The Gnomon of Saint-Sulpice is a scientific instrument built into the floor and transept of the church. It consists of a brass meridian line inlaid into the stone floor, which connects to a tall, white marble obelisk standing near a statue of Saint Peter. High above in the southern transept window, a small opening acts like a lens to focus a beam of sunlight onto this line.