The observations of variation by seamen vary, for the
most part, and are uncertain: partly from error and inexperience,
and the imperfections of the instruments; and partly
from the sea being seldom so calm that the
shadows or lights can remain quite
steady on the instruments.
[CHAP. XIIII].
On the variation under the æquinoctial line,
and near it.
[CHAP. XV].
The variation of the magnetick needle in the great
Æthiopick and American sea, beyond
the æquator.
