CHAP. XIX.
The variation in the interior of large
Continents.
ost of the great seas have great
variations; in some parts, however, they have none, but the true directions are toward the pole. On continents, also, the
magnetick needle often deviates from the meridian, as on the edge of the land and near the borders; but it is generally
accustomed to deviate by a somewhat small arc. In the middle, however, of great regions there are no variations. Hence in
the middle lands of Upper Europe, in the interior of Asia, and in the heart of Africa, of Peru, and in the regions of
North or Mexican America, the versorium rests in the meridian.