g.--E.]

Besides these draughts of such places as Mr Anson, or the ships which
he commanded, have touched at in the course of this expedition, and
the descriptions and directions relating thereto, there is inserted,
in the ensuing work, an ample account, with a chart annexed to it, of
a particular navigation, of which hitherto little more than the name
has been known, except to those immediately employed in it: I mean
the tract described by the Manilla ship, in her passage to Acapulco,
through the northern part of the Pacific-ocean. This material article
is collected from the draughts and journals met with on board the
Manilla galleon, founded on the experience of more than an hundred and
fifty years practice, and corroborated in its principal circumstances
by the concurrent evidence of all the Spanish prisoners taken in that
vessel. And as many of their journals; which I have examined, appear
to have been not ill kept, I presume the chart of that northern ocean,
and the particulars of their routes through it, may be very safely
relied on by future navigators. The advantages which may be drawn from
an exact knowledge of this navigation, and the beneficial projects
which may be formed thereon, both in war and peace, are by no means
proper to be discussed in this place; but they will easily offer
themselves to the skilful in maritime affairs. However, as the Manilla
ships are the only ones which have ever traversed this vast ocean,
except a French straggler or two, which have been afterwards seized on
the coast of Mexico; and as, during near two ages, in which this trade
has been carried on, the Spaniards have secreted with the utmost
care all accounts of their voyages from the rest of the world; these
reasons would alone authorize the insertion of those papers, and would
recommend them to the inquisitive, as a very great improvement in
geography, and worthy of attention, from the singularity of many
circumstances therein recited.

I must add what, in my opinion, is far from being the least
recommendation of these materials, that the observations of the
variations of the compass, which are laid down in the chart from these
Spanish journals, tend greatly to complete the general system of
the magnetic variation, of infinite importance to the commercial and
sea-faring part of mankind. These observations were, though in vain,
often publicly called for by our learned countryman, the late Dr
Halley, and to his immortal reputa