ARMILLA, ARMIL

This article appears in Volume V02, Page 576 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: APO-ARN

ARMILLA, ARMIL or ARMILLARY SPHERE (from the Lat. armilla, a bracelet), an

instrument

INSTRUMENT (Lat. instrumentum, from insincere, to build up, furnish, arrange, prepare)

used in astronomy. In its simplest form, consisting. of a ring fixed in the plane of the

equator

EQUATOR (
Late
- LATE
Lat. aequator, from aequare, to make equal)

, the armilla is oe of the most ancient of astronomical instruments. Slightly developed, it was crossed by another ring fixed in the plane of the meridian. The first was an equinoctial, the second a solstitial armilla. Shadows were used as indices of the sun's position, in combination with angular divisions. When several rings or circles were combined representing Pie

great

GREAT

circles of the heavens, the

instrument

INSTRUMENT (Lat. instrumentum, from insincere, to build up, furnish, arrange, prepare)

became an armillary sphere. Armillae are said to have been in early use in China. Eratosthenes (276196 B.C.) used most probably a solstitial armilla for measuring the obliquity of the ecliptic. Hipparchus (160125 B.c.) probably used an armillary sphere of four rings.

Ptolemy

PTOLEMY (
CLAUDIUS
PTOLEMAEUS)

(c. A.D. 107161) describes his instrument in the Syntaxis (book v. chap. i.), and it is of

great

GREAT

interest

INTEREST

as an example of the armillary sphere passing into the spherical astrolabe. It consisted of a graduated circle inside which another could slide, carrying two small tubes diametrically opposite, the instrument being kept vertical by a plumb-line.
Zenith
From M. Blundeville's Treatise of the first principles of
Cosmography and specially of the Spheare.
Armillary Sphere. A.D. 1636.
No material advance was made on

Ptolemy

PTOLEMY (
CLAUDIUS
PTOLEMAEUS)

's instrument until Tycho Brahe, whose elaborate armillary 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 skeleton

celestial

CELESTIAL, OR STELLAR

globe, the

series

SERIES (a Latin word from serere, to join)

of rings representing the great circles of the heavens, and revolving on an

axis

AXIS (Lat. for " axle ")

within a horizon. With the 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 north pole might suitably have the same ornament as was used to mark N. on the compass card, and so surmounted it with the fleur-de-lys, traditionally chosen for that purpose on the compass by Flavio Gioja in honour of Charles of Anjou, king of Sicily and Naples.
Armillary spheres occur in many old sculptures, paintings and engravings; and from these sources we know that they were made for suspension, for resting on the ground or on a table, for holding by a short handle, or either for holding or for resting on a stand.

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