The armillary sphere takes its name from the Latin word ‘armilla’ which means circle or bracelet. It is indeed constituted of a set of circles or ‘armilla’, here made in wood by Robert Marichy, a wood turner in Arinthod in the Jura department. These ‘armilla’ illustrate the geometry of the descriptive elements of the celestial sphere. A ball symbolizing the Earth is placed in the center of the circles on the axis of the poles and a foot, linked to the fixed horizon, serves as a general support for the ensemble.