perceptible difference of level exists between the upper surfaces of the
Atlantic and the Mediterranean, along the chain of the Pyrenees, or between
the coasts of northern Holland and Marseilles.*
[footnote] *See the numerical results in p. 328-333 of the volume just
named. From the geodesical levelings which, at my request, my friend
General Bolivar caused to be taken by Lloyd and Falmare, in the years 1828
and 1829, it was ascertained that the level of the Pacific is at the utmost
3 1/2 feet higher than that of the Caribbean Sea; and even that at different
hours of the day each of the seas is in turn the higher, according to their
respective hours of flood and ebb. If we reflect that in a distance of 64
miles, comprising 933 stations of observation, an error of three feet would
be very apt to occur, we may say that in these new operations we have
further confirmation of the equilibrium of the waters which communicate
round Cape Horn. (Arago, in the 'Annuaire du Bureau des Longitudes pour'
1831, p. 319.) I had inferred from barometrical observations instituted in
1799 and 1804, that if there were any difference between the level of the
Pacific and the Atlantic (Carribean Sea), it could not exceed three meters
(nine feet three inches). See my 'Relat. Hist.', t. iii., p. 555-557, and
'Annales de Chimie', t. i., p. 55-64. The measurements, which appear to
establish an excess of height for the waters of the Gulf of Mexico, and for
those of the northern part of the Adriatic Sea, obtained by combining the
trigonometrical operations of Delcrois and Choppin with those of the Swiss
and Austrian engineers, are open to many doubts. Notwithstanding the form
of the Adriatic, it is improbable that the level of its waters in its
northern portion should be 28 feet higher than that of the Mediterranean at
Marseilles, and 25 feet higher than the level of the Atlantic Ocean. See my
'Asie Centrale', t. ii., p. 332.
p 305
Disturbances of equilibrium and consequent movements of the waters are
partly irregular and transitory, dependent upon winds, and producing waves
which sometimes, at a distance from the shore and during a storm, rise to a
height of more than 35 feet; partly regular and periodic, occasioned by the
position and attraction of the sun and moon, as the ebb and flow of the
tides; and partly permanent, although less intense, occurring as oceanic
currents. The phenomena of tides, which prevail in all seas (with the
exception of the smaller ones that are completely closed in, and where the
ebbing and flowing waves are scarcely or not at all perceptible), have been
perfectly explained by the Newtonian doctrine, and thus brought "within the
domain of necessary facts." Each of these periodically-recurring
oscillations of the waters of the sea has a duration of somewhat more than
half a day. Although in the open sea they scarcely attain an elevation of a
few feet, they often rise considerably higher where the waves are opposed by
the configuration of the shores, as for instance, at St. Malo and in Nova
Scotia, where they reach the respective elevation of 50 feet, and of 65 to
70 feet. "It has been shown by the analysis of the great geometrician
Laplace, that, supposing the depth to be wholly inconsiderable when compared
with the radius of the earth, the stability of the equilibrium of the sea
requires that the density of its fluid should be less than that of the
earth; and, as we have already seen, the earth's density is in fact five
times greater than that of water. The elevated parts of the land can not
therefore be overflowed, nor can the remains of marine animals found on the
summits of mountains have been conveyed to those localities by any previous
high tides.*
[footnote] *Bessel, 'Ueber Fluth und Ebbe', in Schumacher's 'ahrbuch',
1838, s. 225.
It is no slight
This material taken from pages 305-362
COSMOS: A Sketch of the Physical Description of the Universe, Vol. 1
by Alexander von Humboldt
Translated by E C Otte
from the 1858 Harper & Brothers edition of Cosmos, volume 1
--------------------------------------------------
p 305 [balance of p 305 is in file "09 Humboldt"]
It is no slight
p 306
evidence of the importance of analysis, which is too often regarded with
contempt among the unscientific, that Laplace's perfect theory of tides has
enabled us, in our astronomical ephemerides, to predict the height of
spring-tides at the periods of new and full moon, and thus put the
inhabitants of the sea-shore on their guard against the increased danger
attending these lunar revolutions.
Oceanic currents, which exercise so important an influence on the
intercourse of nations and on the climatic relations of adjacent coasts,
depend conjointly upon various causes, differing alike in nature and
importance. Among these we may reckon the periods at which tides occur in
their progress round the earth; the duration and intensity of prevailing
winds; the modifications of density and specific gravity which the particles
of water undergo in consequence of differences in the temperature and in the
relative quantity of saline contents at different latitudes and depths;*
and, lastly, the horary variations of the atmospheric pressure, successively
propagated from east to west, and occurring with such regularity in the
tropics.
[footnote] *The relative density of the particles of water depends
simultaneously on the temperature and on the amount of the saline contents
-- a circumstance that is not sufficiently borne in mind in considering the
cause of currents. The submarine current, which brings the cold polar water
to the equatorial regions, would follow an exactly opposite course, that is
to say, from the equator toward the poles, if the difference in saline
contents were alone concerned. In this view, the geographical distribution
of temperature and of density in the water of the ocean, under the different
zones of latitude and longitude, is of great importance. The numerous
observations of Lenz (Poggendorf's 'Annalen', bd. xx., 1830, s. 129), and
those of Captain Beechey, collected in his 'Voyage to the Pacific', vol.
ii., p. 727, deserve particular attention. See Humboldt, 'Relat. Hist.', t.
i., p. 74, and 'Asie Centrale', t. iii., p. 346.
These currents present a remarkable spectacle; like rivers of uniform
breadth, they cross the sea in different directions, while the adjacent
strata of water, which remain undisturbed, form, as it were, the banks of
these moving streams. This diffrence between the moving waters and those at
rest is most strikingly manifested where long lines of sea-weed, borne
onward by the current, enable us to estimate its velocity. In the lower
strata of the atmosphere, we may sometimes, during a storm, observe similar
phenomena in the limited aerial current, which is indicated by a narrow line
of trees, which are often found to be overthrown in the midst of a dense
wood.
The general movement of the sea from east to west between
p 307
the tropics (termed the equatorial or rotation currnt) is considered to be
owing to the propagation of tides and to the trade winds. Its direction is
changed by the resistance it experiences from the prominent eastern shores
of continents. The results recently obtained by Daussy regarding the
velocity of this current, estimated from observations made on the distances
traversed by bottles that had purposely been thrown into the sea, agree
within one eighteenth with the velocity of motion (10 French nautical miles,
952 toises each, in 24 hours) which I had found from a comparison with
earlier experiments.*
[footnote] *Humboldt, 'Relat. Hist.', t. i., p. 67; 'Nouvelles Annales des
Voyages', 1839, p. 255.
Christopher Columbus, during his third voyage, when he was seeking to enter
the tropics in the meridian of Teneriffe, wrote in his journal as follows:*
"I regard it as proved that the waters of the sea move from east to west, as
do the heavens ('las aguas van con los cielos'), that is to say, like the
apparent motion of the sun, moon, and stars."
[footnote] *Humboldt, 'Examen Crit. de l'Hist. de la Geogr.', t. iii., p.
100. Columbus adds shortly after (Navarrete, 'Coleccion de los Viages y
Descubrimientos de los Espanoles', t. i., p. 260), that the movement is
strongest in the Caribbean Sea. In fact, Rennell terms this region, "not a
current, but a sea in motion". ('Investigation of Currents', p. 23). 66-74.
The narrow currents, or true oceanic rivers which traverse the sea, bring
warm water into higher and cold water into lower latitudes. To the first
class belongs the celebrated Gulf Stream,* which was known to Anghiera, and
more especially to Sir Humphrey Gilbert in the sixteenth century.
[footnote] *Humboldt, 'Examen Critique', t. ii., p. 250; 'Relat. Hist.', t.
i., p. 66-74.
[footnote] *Petrus Martyr de Anghiera, 'De Rebus Oceanicis et Orbe Novo',
Bas., 1523, Dec. iii., lib. vi., p. 57. See Humboldt, 'Examen Critique', t.
ii., p. 254-257, and t. iii., p. 108.
Its first impulse and origin is to be sought to the south of the Cape of
Good Hope; after a long circuit it pours itself from the Caribbean Sea and
the Mexican Gulf through the Straits of the Bahamas, and, following a course
from south-southwest to north-northeast, continues to recede from the shores
of the United States, until, further deflected to the eastward by the Banks
of Newfoundland, it approaches the European coasts, frequently throwing a
quantity of tropical seeds ('Mimosa scandens, Guilandina bonduc, Dolichos
urens') on the shores of Ireland, the Hebrides, and Norway. The
northeastern prolongation tends to mitigate the cold of the ocean, and to
ameliorate the climate on the most northern extremity of Scandinavia. At
the point where the Gulf Stream
p 308
is deflected from the Banks of Newfoundland toward the east, it sends off
branches to the south near the Azores.*
[footnote] *Humboldt, 'Examen Crit.', t. iii., p. 64-109
This is the situation of the Sargasso Sea, or that great bank of weeds which
so vividly occupied the imagination of Christopher Columbus, and which
Oviedo calls the sea-weed meadows ('Praderias de yerva'). A host of small
marine animals inhabits these tently-moved and evergreen masses of 'Fucus
natans', one of the most generally distributed of the social plants of the
sea.
The counterpart of this current (which in the Atlantic Ocean, between
Africa, America, and Europe, belongs almost exclusively to the northern
hemisphere) is to be found in the South Pacific, where a current prevails,
the effect of whose low temperature on the climate of the adjacent shores I
had an opportunity of observing in the autumn of 1802. It brings the cold
waters of the high southern latitudes to the coast of Chili, follows the
shores of this continent and of Peru, first from south to north, and is then
deflected from the Bay of Arica onward from south-southeast to
north-northwest. At certain seasons of the year the temperature of this
cold oceanic current is, in the tropics, only 60 degrees, while the
undisturbed adjacent water exhibits a temperature of 81.5 degrees and 83.7
degrees. On that part of the shore of South America south of Payta, which
inclines furthest westward, the current is suddenly deflected in the same
direction from the shore, turning so sharply to the west that a ship sailing
northward passes suddenly from cold into warm water.
It is not known to what depth cold and warm oceanic currents propagate their
motion; but the deflection experienced by the South African current, from
the Lagullas Bank, which is fully from 70 to 80 fathoms deep, would seem to
imply the existence of a far-extending propagation. Sand banks and shoals
lying beyond the line of these currents may, as was first discovered by the
admirable Benjamin Franklin, be recognized by the coldness of the water over
them. This depression of the temperature appears to me to depend upon the
fact that, by the propagation of the motion of the sea, deep waters rise to
the margin of the banks and mix with the upper strata. My lamented friend,
Sir Humphrey Davy, ascribed this phenomenon (the knowledge of which is often
of great practical utility in securing the safety of the navigator) to the
descent of the particles of water that had been cooled by nocturnal radiation
p 309
and which remain nearer to the surface, owing to the hinderance placed in
the way of their greater descent by the intervention of sand-banks. By his
observations Franklin may be said to have converted the thermometer into a
sounding line. Mists are frequently found to rest over these depths, owing
to the condensation of the vapor of the atmosphere by the cooled waters. I
have seen such mists in the south of Jamaica, and also in the Pacific,
defining with sharpness and clearness the form of the shoals below them,
appearing to the eye as the aerial reflection of the bottom of the sea. A
still more striking effect of the cooling produced by shoals is manifested
in the higher strata of air, in a somewhat analogous manner to that observed
in the case of flat coral reefs, or sand islands. In the open sea, far from
the land, and when the air is calm, clouds are often observed to rest over
the spots where shoals are situated, and their bearing may then be taken by
the compass in the same manner as that of a high mountain or isolated peak.
Although the surface of the ocean is less rich in living forms than that of
continents, it is not improbable that, on a further investigation of its
depths, its interior may be found to possess a greater richness of organic
life than any other portion of our planet. Charles Darwin, in the agreeable
narrative of his extensive voyages, justly remarks that our forests do not
conceal so many animals as the low woody regions of the ocean, where the
sea-weed rooted to the bottom of the shoals, and the severed branches of
fuci, loosened by the force of the waves and currents, and swimming free,
unfold their delicate foliage, upborne by air-cells.*
[footnote] *[See 'Structure and Distribution of Coral Reefs', by Charles
Darwin, London, 1842. Also, 'Narrative of the Surveying Voyage of H.M.S.
"Fly" in the Eastern Archipelago, during the Years ' 1842-1846, by J. B.
Jukes, Naturalist to the expedition, 1847.] -- Tr.
The application of the microscope increases, in the most striking manner,
our impression of the rich luxuriance of animal life in the ocean, and
reveals to the astonished senses a consciousness of the universality of
life. In the oceanic depths, far exceeding the height of our loftiest
mountain chains, every stratum of water is animated with polygastric
sea-worms, Cyclidiae and Ophrydinae. The waters swarm with countless hosts
of small luminiferous animalcules, Mammaria (of the order of Acalephae),
Crustacea, Peridinea, and circling Nereides, which when attracted to the
surface by peculiar meteorological conditions, convert every wave into a
foaming band of flashing light.
p 310
The abundance of those marine animalcules, and the animal matter yielded by
their rapid decomposition are so vast that the sea water itself becomes a
nutrient fluid to many of the larger animals. However much this richness in
animated forms, and this multitude of the most various and highly-developed
microscopic organisms may agreeably excite the fancy, the imagination is
even more seriously, and, I might say, more solemnly moved by the impression
of boundlessness and immeasureability, which are presented to the mind by
every sea voyage. All who possess an ordinary degree of mental activity,
and delight to create to themselves an inner world of thought, must be
penetrated with the sublime image of the infinite, when gazing around them
on the vast and boundless sea, when involuntarily the glance is attracted to
the distant horizon, where air and water blend together, and the stars
continually rise and set before the eyes of the mariner. This contemplation
of the eternal play of the elements is clouded, like every human joy, by a
touch of sadness and of longing.
A peculiar predilection for the sea, and a grateful remenbrance of the
impression which it has excited in my mind, when I have seen it in the
tropics in the calm of nocturnal rest, or in the fury of the tempest, have
alone induced me to speak of the individual enjoyment afforded by its aspect
before I entered upon the consideration of the favorable influence which the
proximity of the ocean has incontrovertibly exercised on the cultivation of
the intellect and character of many nations, by the multiplication of those
bands which ought to encircle the whole of humanity, by affording additional
means of arriving at a knowledge of the configuration of the earth, and
furthering the advancement of astronomy, and of all other mathematical and
physical sciences. A portion of this influence was at first limited to the
Mediterranean and the shores of southwestern Africa, but from the sixteenth
century it has widely spread, extending to nations who live at a distance
from the sea, in the interior of continents. Since Columbus was sent to
"unchain the ocean"* (as the unknown voice whispered to him in a dream when
he lay on a sick-bed near
p 311
the River Belem), man has ever boldly ventured onward toward the discovery
of unknown regions.
[footnote] *The voice addressed him in these words, "Maravillosamente Dios
hizo sonar tu nombre en la tierra; de los atamientos de la mar Oceana, que
estaban cerrados con cadenas tan fuertes, te dió las llaves" -- "God will
cause thy name to be wonderfully resounded through the earth, and give thee
the keys of the gates of the ocean, which are closed with strong chains."
The dream of Columbus is related in the letter to the Catholic monarchs of
July the 7th, 1503. (Humboldt, 'Examen Critique', t. iii., p. 234.)
The second external and general covering of our planet, the aerial ocean, in
the lower strata, and on the shoals of which we live, presents six classes
of natural phenomena, which manifest the most intimate connection with one
another. They are dependent on the chemical composition of the atmosphere,
the variations in its transparency, polarization, and color, its density or
pressure, its temperature and humidity, and its electricity. The air
contains in oxygen the first element of physical animal life, and besides
this benefit, it possesses another, which may be said to be of a nearly
equally high character, namely, that of conveying sound; a faculty by which
it likewise becomes the conveying sound; a faculty by which it likewise
becomes the conveyer of speech and the means of communicating thought, and
consequently of maintaining social intercourse. If the Earth were deprived
of an atmosphere, as we suppose our moon to be, it would present itself to
our imagination as a soundless desert.
The relative quantities of the substances composing the strata of air
accessible to us have, since the beginning of the nineteenth century, become
the object of investigations, in which Gay-Lussac and myself have taken an
active part; it is however, only very recently that the admirable labors of
Dumas and Boussingault have, by new and more accurate methods, brought the
chemical analysis of the atmosphere to a high degree of perfection.
According to this analysis, a volume of dry air contains 20.8 of oxygen, and
79.2 of nitrogen, besides from two to five thousandth parts of carbonic acid
gas, a still smaller quantity of carbureted hydrogen gas,* and, according to
the important experiments of Saussure and Liebig, traces of ammoniacal
vapors,** from which plants derive their nitrogenous contents.
[footnote] *Boussingault, 'Recherches sur la Composition de l'Atmosphere',
in the 'Annales de Chimie et de Physique', t. lvii., 1834, p. 171-173; and
lxxi. 1839, p. 116. According to Boussingault and Lewy, the proportion of
carbonic acid in the atmosphere at Audilly, at a distance, therefore, from
the exhalations of a city, varied only between 0.00028 and 0.00031 in volume.
[footnote] **Liebig, in his important work, entitles 'Die Organische Chemie
in ihrer Anwendung auf Agricultur und Physiologie', 1840, s. 62-72. On the
influence of atmospheric electricity in the production of nitrate of
ammonia, which, coming into contact with carbonate of lime, is changed into
carbonate of ammonia, see Boussingault's 'Economie Rurale consideree dans
ses Rapports avec la Chimie et la Meteorologie', 1844, t. ii., p. 247, 267,
and t. i., p. 84.
Some observations of Lewy render it probable that the quantity of oxygen
varies perceptibly
p 312
but slightly, over the sea and in the interior of continents, according to
local conditions or to the seasons of the year. We may easily conceive that
changes in the oxygen held in solution in the sea, produced by microscopic
animal organisms, may be attended by alterations in the strata of air in
immediate contact with it.*
[footnote] *Lewy, in the 'Comptes Rendus de l'Acad. des Sciences', t.
xvii., Part ii., p. 235-248.
The air which Martins collected at Faulhorn at an elevation of 8767 feet,
contained as much oxygen as the air at Paris.*
[footnote] *Dumas, in the 'Annales de Chimie, 3e Serie', t. iii., 1841, p.
257.
The admixture of carbonate of ammonia in the atmosphere may probably be
considered as older than the existence of organic beings on the surface of
the earth. The sources from which carbonic acid* may be yielded to the
atmosphere are most numerous.
[footnote] *In this enumeration, the exhalation of carbonic acid by plants
during the night, while they inhale oxygen, is not taken into account,
because the increase of carbonic acid from this source is amply
counter-balanced by the respiratory process of plants during the day. See
Boussingault's 'Econ. Rurale', t. i., p. 53-68, and Liebig's 'Organische
Chemie', s. 16, 21.
In the first place we would mention the respiration of animals, who receive
the carbon which they inhale from vegetable food, while vegetables receive
it from the atmosphere; in the next place, carbon is supplied from the
interior of the earth in the vicinity of exhausted volcanoes and thermal
springs, from the decomposition of a small quantity of carbureted hydrogen
gas in the atmosphere, and from the electric discharges of clouds, which are
of such frequent occurrence within the tropics. Besides these substances,
which we have considered as appertaining to the atmosphere at all heights
that are accessible to us, there are others accidentally mixed with them,
especially near the ground, which sometimes, in the form of miasmatic and
gaseous contagia, exercise a noxious influence on animal organization.
Their chemical nature has not yet been ascertained by direct analysis; but,
from the consideration of the processes of decay which are perpetually going
on in the animal and vegetable substances with which the surface of our
planet is covered, and judging from analogies deduced from the comain of
pathology, we are led to infer the existence of such noxious local
admixtures. Ammoniacal and other nitrogenous vapors, sulphureted hydrogen
gas, and compounds analogous to the polybasic ternary and quaternary
compounds analogous to the polybasic ternary and quaternary combinations of
the vegetable kingdom, may produce miasmata,*
p 313
which, under various forms, may generate ague and typhus fever (not by any
means exclusively on wet, marshy ground, or on coasts covered by putrescent
mollusca, and low bushes of 'Rhizophora mangle' and Avicennia).
[footnote] *Gay-Lussac, in 'Annales de Chimie', t. liii., p. 120; Payen,
Mem. sur la Composition Chimique des Vegetaux, p. 36, 42; Liebig, 'Org.
Chemie', s. 229-345; Boussingault, 'Econ. Rurale', t. i., p. 142-153.