This type of registering barometer, or barometrograph, was invented by Felice Fontana and built at the Museo di Fisica e Storia Naturale. A siphon barometric tube of iron and glass is mounted on a marble base. A floating weight sliding into the shorter arm of the siphon is connected to a brass balance mechanism with counterweights and mounted on frictionless wheels. A paper ribbon is stretched on the balance mechanism, which carries the barometric scale in Paris inches. Above the balance mechanism is a clock, fixed to the marble base by means of a support. The clockwork activates a metal pointer that perforates the paper ribbon at regular intervals. The pointer's lateral motion prevents it from perforating the same point again, even in the absence of pressure changes. The series of perforations thus forms a record of pressure variations over time.