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"Armillary Sphere, an instrument used in astronomy. In its simplest form, consisting of a ring fixed in the plane of the equator, the armilla is one of the most ancient of astronomical instruments. Slightly developed, it was crossed by another ring fixed in the plane of the meridian." — The Encyclopedia Britannica, 1910

Armilla

"Armillary Sphere, an instrument used in astronomy. In its simplest form, consisting of a ring fixed…

"A number of rings arranged round a centre, so as to represent a sphere; used to illustrate the relative positions of the ecliptic, equator, etc., of the celestial sphere." — Williams, 1889

Armillary sphere

"A number of rings arranged round a centre, so as to represent a sphere; used to illustrate the relative…