An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) An enclosure, usually made with bars or wire, for keeping birds or wild animals.
2) An enclosed structure resembling a cage. → observer's cage, → Faraday cage.

M.E. from O.Fr. cage, from L. cavea "hollow place, enclosure for animals," cognate with Pers. kâv "hollow," → concave.

Qafas "cage," of unknown origin.

An enclosure made of conducting material, such as wire mesh or metal plates, that shields what it contains from external electric fields. According to → Gauss's theorem, the electric field inside a hollow conductor is nil. In order to demonstrate this, Faraday, in 1836, made a large box covered with wire mesh, and went inside it himself with an → electroscope. Powerful charges were applied to the outside of the box, but he detected no effect inside the cage.

→ farad; → cage.

A place located either at the top of the tube of a large telescope from where one observes or at the back of the tube where instruments are attached to the → Cassegrain focus.

→ observer; → cage.