1911 Encyclopædia Britannica/Armature

ARMATURE (from Lat. armatura, armour), a covering for defence. In zoology the word is used of the bony shell of the armadillo. In architecture it is applied to the iron stays by which the lead lights are secured in windows. (See Stanchion and Saddle: Saddle-Bars.) In magnetism Dr William Gilbert applied the term to the piece of soft iron with which he “armed” or capped the lodestone in order to increase its power. It is also used for the “keeper” or piece of iron which is placed across the poles of a horse-shoe magnet, and held in place by magnetic attraction, in order to complete the magnetic circuit and preserve the magnetism of the steel; and hence, in dynamo-electric machinery, for the portion which is attracted by the electromagnet, as the moving part of an electric motor, or, by extension, the moving part of a dynamo (q.v.).