On August 14, 1642, I sailed from Batavia with two vessels; the one
called the _Heemskirk_, and the other the _Zee-Haan_. On September 5 I
anchored at Maurice Island, in the latitude of 20 degrees south, and in
the longitude of 83 degrees 48 minutes. I found this island fifty German
miles more to the east than I expected; that is to say, 3 degrees 33
minutes of longitude. This island was so called from Prince Maurice,
being before known by the name of Cerne. It is about fifteen leagues in
circumference, and has a very fine harbour, at the entrance of which
there is one hundred fathoms water. The country is mountainous; but the
mountains are covered with green trees. The tops of these mountains are
so high that they are lost in the clouds, and are frequently covered by
thick exhalations or smoke that ascends from them. The air of this
island is extremely wholesome. It is well furnished with flesh and fowl;
and the sea on its coasts abounds with all sorts of fish. The finest
ebony in the world grows here. It is a tall, straight tree of a moderate
thickness, covered with a green bark, very thick, under which the wood is
as black as pitch, and as close as ivory. There are other trees on the
island, which are of a bright red, and a third sort as yellow as wax. The
ships belonging to the East India Company commonly touch at this island
for refreshments on their passage to Batavia.
I left this island on the 8th of October, and continued my course to the
south to the latitude of 40 degrees or 41 degrees, having a strong north-
west wind; and finding the needle vary 23, 24, and 25 degrees to the 22nd
of October, I sailed from that time to the 29th to the east, inclining a
little to the south, till I arrived in the latitude of 45 degrees 47
minutes south, and in the longitude of 89 degrees 44 minutes; and then
observed the variation of the needle to be 26 degrees 45 minutes towards
the west.
As our author was extremely careful in this particular, and observed the
variation of the needle with the utmost diligence, it may not be amiss to
take this opportunity of explaining this point, so that the importance of
his remarks may sufficiently appear. The needle points exactly north
only in a few places, and perhaps not constantly in them; but in most it
declines a little to the east, or to the west, whence arises eastern and
western declination: when this was first observed, it was attributed to
certain excavations or hollows in the earth, to veins of lead, stone, and
other such-like causes. But when it was found by repeated experiments
that this variation varied, it appeared plainly that none of those causes
could take place; since if they had, the variation in the same place must
always have been the same, whereas the fact is otherwise.
Here at London, for instance, in the year 1580, the variation was
observed to be 11 degrees 17 minutes to the east; in the year 1666, the
variation was here 34 minutes to the west; and in the year 1734, the
variation was somewhat more than 1 degree west. In order to find the
variation of the needle with the least error possible, the seamen take
this method: they observe the point the sun is in by the compass, any
time after its rising, and then take the altitude of the sun; and in the
afternoon they observe when the sun comes to the same altitude, and
observe the point the sun is then in by the compass; for the middle,
between these two, is the true north or south point of the compass; and
the difference between that and the north or south upon the card, which
is pointed out by the needle, is the variation of the compass, and shows
how much the north and south, given by the compass, deviates from the
true north and south points of the horizon. It appears clearly, from
what has been said, that in order to arrive at the certain knowledge of
the variation, and of the variation of that variation of the compass, it
is absolutely requisite to have from time to time distinct accounts of
the variation as it is observed in different places: whence the
importance of Captain Tasman's remarks, in this respect, sufficiently
appears. It is true that the learned and ingenious Dr. Halley has given
a very probable account of this matter; but as the probability of that
account arises only from its agreement with observations, it follows
those are as necessary and as important as ever, in order to strengthen
and confirm it.