half a rumbe from the needles toward the
west), nor its use in taking the variation. Hence, while they show the
variation of the compass in different places, it is uncertain whether they
measure the deviation by a true meridional compass or by some other whose
needles are displaced from the lily. The Portuguese (as is patent in their
writings) make use of the Portuguese compass, whose magnetick needles are
fixed aside from the lily by half of one rumbe toward the east. Moreover on
the sea the observation of the variation is a matter of great difficulty,
on account of the motion of the ship and the uncertainty of the deviation,
even with the more skilful observers, if they use the best made instruments
hitherto known and used. Hence there arise different opinions concerning
the magnetick deviation: as, for instance, near the Island of St. Helena
the Portuguese Rodriguez de {178} Lagos measures half a rumbe. The Dutch in
their nautical log fix it at a whole rumbe. Kendall, the expert Englishman,
with a true meridional compass admits only a sixth part of a rumbe. A
little to the East of Cape Agullias Diego Alfonso makes no variation, and
shows by an Astrolabe that the compass remains in the true meridian.
Rodriguez shows that the compass at Cape Agulhas has no variation if it is
of Portuguese construction, in which the needles are inclined half a rumbe
to the East. And there is the same confusion, negligence, and vanity in
very many other instances.

* * * * *

CHAP. XIIII.

On the variation under the aequinoctial line,
_and near it_.

In the North the magnetick needle varies because of the Boreal eminences of
the continent; in the South because of the Austral; at the aequator, if the
regions on both sides were equal, there would be no variation. But because
this rarely happens some variation is often observed under the aequator;
and even at some distance from the aequator of three or 4 degrees toward
the North, there may be a variation arising from the south, if those very
wide and influential southern continents be somewhat near on one side.

* * * * *

CHAP. XV.

The variation of the magnetick needle in the great
Aethiopick and American sea, beyond
_the aequator_.

Discourse hath already been had of the mode and reason of the variation in
the great Atlantick Ocean: but when one has advanced beyond the aequator
off the east coast of Brazil the m