The variation in the interior of large
_Continents_.
Most 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.
* * * * *