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ARMILLA, ARMIL

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Originally appearing in Volume V02, Page 576 of the 1911 Encyclopedia Britannica.
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ARMILLA, ARMIL or ARMILLARY See also:SPHERE (from the See also:Lat. armilla, a See also:bracelet), an See also:instrument used in See also:astronomy. In its simplest See also:form, consisting. of a See also:ring fixed in the See also:plane of the See also:equator, the armilla is oe of the most See also:ancient of astronomical See also:instruments. Slightly See also:developed, it was crossed by another ring fixed in the plane of the See also:meridian. The first was an equinoctial, the second a solstitial armilla. Shadows were used as indices of the See also:sun's position, in See also:combination with angular divisions. When several rings or circles were combined representing See also:Pie See also:great circles of the heavens, the instrument became an armillary sphere. Armillae are said to have been in See also:early use in See also:China. Eratosthenes (276–196 B.C.) used most probably a solstitial armilla for measuring the obliquity of the See also:ecliptic. See also:Hipparchus (160–125 B.c.) probably used an armillary sphere of four rings. See also:Ptolemy (c. A.D. 107—161) describes his instrument in the Syntaxis (See also:book v. See also:chap. i.), and it is of great See also:interest as an example of the armillary sphere passing into the spherical See also:astrolabe.

It consisted of a graduated circle inside which another could slide, carrying two small tubes diametrically opposite, the instrument being kept See also:

vertical by a plumb-See also:line. See also:Zenith From M. Blundeville's See also:Treatise of the first principles of Cosmography and specially of the Spheare. Armillary Sphere. A.D. 1636. No material advance was made on Ptolemy's instrument until Tycho See also:Brahe, whose elaborate armillary See also:spheres passing into astrolabes are figured in his Astron'miae Instauratae Mechanica. 576 The armillary sphere survives as useful for teaching, and may be described as a See also:skeleton See also:celestial globe, the See also:series of rings representing the great circles of the heavens, and revolving on an See also:axis within a See also:horizon. With the See also:earth as centre such a sphere is known as Ptolemaic; with the sun as centre, as Copernican. The designer of the instrument shown no doubt thought, that the See also:north See also:pole might suitably have the same See also:ornament as was used to See also:mark N. on the See also:compass card, and so surmounted it with the fleur-de-lys, traditionally chosen for that purpose on the compass by Flavio See also:Gioja in See also:honour of See also:Charles of See also:Anjou, See also:king of See also:Sicily and See also:Naples. Armillary spheres occur in many old sculptures, paintings and engravings; and from these See also:sources we know that they were made for suspension, for resting on the ground or on a table, for holding by a See also:short handle, or either for holding or for resting on a stand.

End of Article: ARMILLA, ARMIL

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