Astatic

Astatic, 'without polarity' (from the Greek), used most frequently of a magnetic needle so arranged as to be unaffected by the earth's magnetism. This is managed by taking two magnetic needles, as nearly of the same intensity as possible, and placing them parallel to one another, with their poles in opposite directions. They thus neutralise one another, so as to be unaffected by the earth's magnetism, though they remain subject to galvanic action. This compound astatic needle forms the principal part of the astatic galvanometer.