Personal Narrative Of Travels To The Equinoctial Regions Of America During The Years 1799-1804 - Volume 1 - By Alexander Von Humboldt And Aime Bonpland.
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As the long and
narrow passage by which a ship sails from the port of Corunna opens
towards the north, and the wind was contrary, we made eight short
tacks, three of which were useless.
A fresh tack was made, but very
slowly, and we were for some moments in danger at the foot of fort
St. Amarro, the current having driven us very near the rock, on
which the sea breaks with considerable violence. We remained with
our eyes fixed on the castle of St. Antonio, where the unfortunate
Malaspina was then a captive in a state prison. On the point of
leaving Europe to visit the countries which this illustrious
traveller had visited with so much advantage, I could have wished
to have fixed my thoughts on some object less affecting.
At half-past six we passed the Tower of Hercules, which is the
lighthouse of Corunna, as already mentioned, and where, from a very
remote time, a coal-fire has been kept up for the direction of
vessels. The light of this fire is in no way proportionate to the
noble construction of so vast an edifice, being so feeble that
ships cannot perceive it till they are in danger of striking on the
shore. Towards the close of day the wind increased and the sea ran
high. We directed our course to north-west, in order to avoid the
English frigates, which we supposed were cruising off these coasts.
About nine we spied the light of a fishing-hut at Sisarga, which
was the last object we beheld in the west of Europe.
On the 7th we were in the latitude of Cape Finisterre. The group of
granitic rocks, which forms part of this promontory, like that of
Torianes and Monte de Corcubion, bears the name of the Sierra de
Torinona. Cape Finisterre is lower than the neighbouring lands, but
the Torinona is visible at seventeen leagues' distance, which
proves that the elevation of its highest summit is not less than
300 toises (582 metres). Spanish navigators affirm that on these
coasts the magnetic variation differs extremely from that observed
at sea. M. Bory, it is true, in the voyage of the sloop Amaranth,
found in 1751, that the variation of the needle determined at the
Cape was four degrees less than could have been conjectured from
the observations made at the same period along the coasts. In the
same manner as the granite of Galicia contains tin disseminated in
its mass, that of Cape Finisterre probably contains micaceous iron.
In the mountains of the Upper Palatinate there are granitic rocks
in which crystals of micaceous iron take the place of common mica.
On the 8th, at sunset, we descried from the mast-head an English
convoy sailing along the coast, and steering towards south-east. In
order to avoid it we altered our course during the night. From this
moment no light was permitted in the great cabin, to prevent our
being seen at a distance. This precaution, which was at the time
prescribed in the regulations of the packet-ships of the Spanish
navy, was extremely irksome to us during the voyages we made in the
course of the five following years. We were constantly obliged to
make use of dark-lanterns to examine the temperature of the water,
or to read the divisions on the limb of the astronomical
instruments. In the torrid zone, where twilight lasts but a few
minutes, our operations ceased almost at six in the evening. This
state of things was so much the more vexatious to me as from the
nature of my constitution I never was subject to sea-sickness, and
feel an extreme ardour for study during the whole time I am at sea.
On the 9th of June, in latitude 39 degrees 50 minutes, and
longitude 16 degrees 10 minutes west of the meridian of the
observatory of Paris, we began to feel the effects of the great
current which from the Azores flows towards the straits of
Gibraltar and the Canary Islands. This current is commonly
attributed to that tendency towards the east, which the straits of
Gibraltar give to the waters of the Atlantic Ocean. M. de Fleurieu
observes that the Mediterranean, losing by evaporation more water
than the rivers can supply, causes a movement in the neighbouring
ocean, and that the influence of the straits is felt at the
distance of six hundred leagues. Without derogating from the
respect I entertain for the opinion of that celebrated navigator, I
may be permitted to consider this important object in a far more
general point of view.
When we cast our eyes over the Atlantic, or that deep valley which
divides the western coasts of Europe and Africa from the eastern
coasts of the new world, we distinguish a contrary direction in the
motion of the waters. Within the tropics, especially from the coast
of Senegal to the Caribbean Sea, the general current, that which
was earliest known to mariners, flows constantly from east to west.
This is called the equinoctial current. Its mean rapidity,
corresponding to different latitudes, is nearly the same in the
Atlantic and in the Pacific, and may be estimated at nine or ten
miles in twenty-four hours, consequently from 0.59 to 0.65 of a
foot every second! In those latitudes the waters run towards the
west with a velocity equal to a fourth of the rapidity of the
greater part of the larger rivers of Europe. The movement of the
ocean in a direction contrary to that of the rotation of the globe,
is probably connected with this last phenomenon only as far as the
rotation converts into trade winds* (* The limits of the trade
winds were, for the first time, determined by Dampier in 1666.) the
polar winds, which, in the low regions of the atmosphere bring back
the cold air of the high latitudes toward the equator.
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