follows the variations of temperature in the atmosphere, and how the sea
acts in equalizing temperatures, moderating simultaneously the severity of
winter and the heat of summer. Hence arises a second more important
contrast -- that, namely, between insular and littoral climates enjoyed by
all articulated continents having deeply indented bays and peninsulas, and
between the climate of the interior of great masses of solid land. This
remarkable contrast has been fully
p 322
developed by Leopold von Buch in all its various phenomena, both with
respect to its influence on vegetation and agriculrure, on the transparency
of the atmosphere, the radiation of the soil, and the elevation of the line
of perpetual snow. In the interior of the Asiatic Continent, Tobolsk,
Barnaul on the Oby, and Irkutsk, have the same mean summer heat as Berlin,
Munster, and Cherbourg in Normandy, the thermometer sometimes remaining for
weeks together at 86 degrees or 88 degrees, while the mean winter
temperature is, during the coldest month, as low as -0.4 degrees to -4
degrees. These continental climates have therefore justly been termed
'excessive' by the great mathematician and physicist Buffon; and the
inhabitants who live in countries having such 'excessive' climates seem
almost condemned, as Dante expresses himself,
"A sofferir tormenti caldi e geli."*
[fiitbite] *Dante, 'Divina Commedia, Purgatorio', canto iii.
In no portion of the earth, neither in the Canary Islands, in Spain, nor in
the south of France, have I ever seen more luxuriant fruit, especially
grapes, than in Astrachan, near the shores of the Caspian Sea (46 degrees
21'). Although the mean annual temperature is about 48ºdegrees, the mean
summer heat rises to 70ºdegrees, as at Bordeaux, while not only there, but
also further to the south, as at Kislar on the mouth of the Terek (in the
latitude of Avignon and Rimini), the thermometer sinks in the winter to -13
degrees or -22 degrees.
Ireland, Guernsey, and Jersey, the peninsula of Brittany, the coasts of
Normandy, and of the south of England, present, by the mildness of their
winters, and by the low temperature and clouded sky of their summers, the
most striking contrast to the continental climate of the interior of Eastern
Europe. In the northeast of Ireland (54 degrees 56'), lying under the same
parallel of latitude as Konigsberg in Prussia, the myrtle blooms as
luxuriantly as in Portugal. The mean temperature of the month of August,
which in Hungary rises to 70 degrees, scarcely reaches 61 degrees at Dublin,
which is situated on the same isothermal line of 49 degrees; the mean winter
temperature, which falls to about 28 degrees at Pesth, is 40 degrees at
Dublin (whose mean annual temperature is not more than 49 degrees); 3.6
degrees higher than that of Milan, Pavia, Padua, and the whole of Lombardy,
where the mean annual temperature is upward of 55ºdegrees. At Stromness,
in the Orkneys, scarcely half a degree further south than Stockholm, the
winter temperature is 39 degrees, and consequently higher than that of
Paris, and neary as high as that of London.
p 323
Even in the Faroe Islands, at 62 degrees latitude, the inland waters never
freeze, owing to the favoring influence of the west winds and of the sea.
On the charming coasts of Devonshire, near Salcombe Bay, which has been
termed, on account of the mildness of its climate, the 'Montpellier of the
North', the Agave Mexicana has been seen to blossoom in the open air, while
orange-trees trained against espaliers, and only slightly protected by
matting, are found to bear fruit. There, as well as at Penzance and
Gosport, and at Cherbourg on the coast of Normandy, the mean winter
temperature exceeds 42 degrees, falling short by only 2.4 degrees of the
mean winter temperature of Montpellier and Florence.*
[footnote] *Humboldt, 'Sur les Lignes Isothermes', in the 'Memoires de
Physique et de Chimie de la Societe d'Arcueil', t. iii., Paris, 1817, p.
143-165; Knight, in the 'Transactions of the Horticultural Society of
London', vol. i, p. 32; Watson, 'Remarks on the Geographical Distribution of
British Plants', 1835, p. 60; Trevelyan, in Jemieson's 'Edinburgh New Phil.
Journal', No. 18, p. 154; Mahlmann in his admirable German translation of my
'Asie Centrale', th. ii., s. 60.
These observations will suffice to show the important influence exercised on
vegetation and agriculture, on the cultivation of fruit, and on the comfort
of mankind, by differences in the distribution of the same mean annual
temperature, through the different seasons of the year.
The lines which I have termed 'Isochimenal' and 'isotheral' (lines of equal
winter and equal summer temperature) are by no means parallel with the
'isothermal' lines (lines of equal annual temperature). If, for instance,
in countries where myrtles grow wild, and the earth does not remain covered
with snow in the winter, the temperature of the summer and autumn is barely
sufficient to bring apples to perfect ripeness, and if, again, we observe
that the grape rarely attains the ripeness necessary to convert it into
wine, either in islands or in the vicinity of the sea, even when cultivated
on a western coast, the reason must not be sought only in the low degree of
summer heat, indicated, in littoral situations, by the thermometer when
suspended in the shade, but likewise in another cause that has not hitherto
been sufficiently considered, although it exercises an active influence on
many other phenomena (as, for instance, in the inflammation of a mixture of
chlorine and hydrogen), namely the difference between direct and diffused
light, or that which prevails when the sky is clear and when it is overcast
by mist. I long since endeavored to attract the attention of physicists and
physiologists* to this
p 324
difference, and to the 'unmeasured' heat which is locally developed in the
living vegetable cell by the action of direct light.
[footnote] *"Haec de temperie aeris, qui terram late circumfundit, ac in
quo, longe a solo, instrumenta nostra meteorologica suspensa habemus. Sed
alia est caloris vis, quem radii solis nullis nubibus velati, in foliis
ipsia et fructibus maturescentibus, magis minusve coloratis, gignunt,
quemque, ut egregia demonstrant experimenta amicissimorum Gay-Lussacii et
Thenardi de combustione chlori et hydrogenis, ope thermometri metiri nequis.
Etenim locis planis et montanis, vento libe spirante, circumfusi aeris
temperies cadem esse potest coelo sudo vel nebuloso; ideoque ex
observationibus solis thermometricis, nullo adhibito Photometro, haud
cognosces, quam ob causam Galliae septentrionalis tractur Armoricanus et
Nervicus, versus littora, coe temperato sed sole raro utentia, Vitem fere
non tolerant. Egent enim stirpes non solum caloris stimulo, sed et lucis,
quae magis intensa locis excelsis quam planis, duplici modo plantas movet,
vi sua tum propria, tum calorem in superficie earum excitante." -- Humboldt,
'De Distributione Geographica Plantarum', 1817, p. 163-164.
If, in forming a thermic scale of different kinds of cultivation,* we begin
with those plants which require the hottest climate, as the vanilla, the
cacao, banana, and cocoa-nut, and proceed to the pine-apples, the
sugar-cane, coffee, fruit-bearing date-trees, the cotton-tree, citrons,
olives, edible chestnuts, and fines producing potable wine, an exact
geographical consideration of the limits of cultivation, both on plains and
on the declivities of mountains, will teach us that other climatic relations
besides those of mean annual temperature are involved in these phenomena.
[footnote] *Humboldt, op. cit., p. 156-161; Meyen, in his 'Grundriss der
Pflanzengeographie', 1836 s. 379-467; Boussingault, 'Economie Rurale', t.
ii., p. 675.
Taking an example, for instance, from the cultivation of the vine, we find
that, in order to procure 'potable' wine,* it is requisite that the mean
annual heat should exceed 49 degrees, that the winter temperature upward of
64 degrees.
[footnote] *the following table illustrates the cultivation of the vine in
Europe, and also the depreciation of its produce according to climatic
relations. See my 'Asie Centrale', t. iii., p. 159. The examples quoted in
the text for Bordeaux and Potsdam are, in respect of numerical relation,
alike applicable to the countries of the Rhine and Maine (48 degrees 35' to
40 degrees 7' N. lat.). Cherbourg in Normandy, and Ireland, show in th most
remarkable manner how, with thermal relations very nearly similar to those
prevailing in the interior of the Continent (as estimated by the thermometer
in the shade), the results are nevertheless extremely different as regards
the ripeness or the unripeness of the fruit of the vine, this difference
undoubtedly depending on the circumstance whether the vegetation of the
plant proceeds under a bright sunny sky, or under a sky that is habitually
obscured by clouds:
[NB Table will line up in Courier 10 point]
_____________________________________________________________________
Places. Lat- Ele- Mean Win- Spring. Sum- Aut- Number of the
it- va- of the ter. mer. umn. years of the
tude tion. Year. observation
_____________________________________________________________________
deg ' Eng.ft. Fahr.
Bordeaux 44 50 25.6 57.0 43.0 56.0 71.0 58.0 10
Stras- 48 35 479.0 49.6 34.5 50.0 64.6 50.0 35
bourg
Heid- 49 24 333.5 59.5 34.0 50.0 64.3 49.7 20
elberg
Manheim 49 29 300.5 50.6 34.6 50.8 67.1 49.5 12
Wurzburg 49 48 562.5 50.2 35.5 50.5 65.7 49.4 27
Frank-
fort on
Maine 50 7 388.5 49.5 33.3 50.0 64.4 49.4 19
Berlin 52 31 102.3 47.5 31.0 46.6 63.6 47.5 23
Cher-
bourg (no
wine) 49 39 .... 52.1 41.5 50.8 61.7 54.2 3
Dublin
(ditto) 53 23 .... 49.1 40.2 47.1 59.6 49.7 13
___________________________________________________________________
The great accordance in the distribution of the annual temperature through
the different seasons, as presented by the results obtained for the valleys
of the Rhine and Maine, tends to confirm the accuracy of these
meteorological observations. The months of December, January, and February
are reckoned as winter months. When the different qualities of the wines
produced in Franconia, and in the countries around the Baltic, are compared
with the mean summer and autumn temperature of Wurzburg and Berlin, we are
almost surprised to find a difference of only about two degrees. The
difference in the spring is about four degrees. The influence of late May
frosts on the flowering season, and after a correspondingly cold winter, is
almost as important an element as the time of the subsequent ripening of the
grape. The difference alluded to in the text between the true temperature
of the surface of the ground and the indications of a thermometer suspended
in the shade and protected from extraneous influences, is inferred by Dove
from a consideration of the results of fifteen years' observations made at
the Chiswick Gardens. See Dove, in 'Bericht uber die Verhandl. der Berl.
Akad. der Wiss.', August, 1844, s. 285.
At Bordeaux, in the valley of the Garonne (44 degrees 50' lat.), the mean
annual winter, summer, and autumn temperatures are respectively 57 degrees,
43 degrees, 71 degrees, and 58 degrees. In the plains near the
p 325
Baltic (52 degrees 30' lat.), where a wine is produced that can scarcely be
considered potable, these numbers are as follows: 47.5 degrees, 30 degrees,
63.7 degrees, and 47.5 degrees. If it should appear strange that the great
differences indicated by the influence of climate on the production of wine
should not be more clearly manifested by our thermometers, the circumstance
will appear less singular when we remember that a thermometer standing in
the shade, and protected from the effect of direct insolation and nocturnal
radiation can not, at all seasong of the year, and during all periodic
changes of heat, indicate the true superficial temperature of the ground
exposed to the whole effect of the sun's rays.
The same relations which exist between the equable littoral climate of the
peninsula of Brittany, and the lower winter and
p 326
higher summer temperature of the remainder of the continent of France, are
likewise manifested in some degree, between Europe and the great continent
of Asia, of which the former may be considered to constitute the western
peninsula. Europe owes its milder climate, in the first place, to its
position with respect to Africa, whose wide extent of tropical land is
favorable to the ascending current, while the equatorial region to the south
of Asia is almost wholly oceanic; and next to its deeply-articulated
configuration, to the vicinity of the ocean on its western shores; and,
lastly, to the existence of an open sea, which bounds its northern confines.
Europe would therefore become colder* if Africa were to be overflowed by
the ocean; of if the mythical Atlantis were to arise and connect Europe with
North America; or if the Gulf Stream were no longer to diffuse the warming
influence of its waters into the North Sea; or if, finally, another mass of
solid land should be upheaved by volcanic action, and interposed between the
Scandinavian peninsula and Spitzbergen.
[footnote] *See my memoir, 'Ueber die Haupt-Ursachen der
Temperaturverschiedenheit auf der Erdoberfläche', in the 'Abhandl. der
Akad. der Wissensch. zu Berlin von dem Jahr' 1827, s. 311.
If we observe that in Europe the mean annual temperature falls as we
proceed, from west to east, under the same parallel of latitude, from the
Atlantic shores of France through Germany, Poland, and Russia, toward the
Uralian Mountains, the main cause of this phenomenon of increasing cold must
be sought in the form of the continent (which becomes less indented, and
wider, and more compact as we advance), in the increasing distance from
seas, and in the diminished influence of westerly winds. Beyond the Uralian
Mountains these winds are converted into cool land-winds, blowing over
extended tracts covered with ice and show. The cold of western Siberia is
to be ascribed to these relations of configuration and atmospheric currents,
and not -- as Hippocrates and Trogus Pompeius, and even celebrated travelers
of the eighteenth century conjectures -- to the great elevation of the soil
above the level of the sea.*
[footnote] *The general level of Siberia, from Tobolsk, Tomsk, and Barnaul,
from the Altai Mountains to the Polar Sea, is not so high as that of Mauheim
and Dresden; indeed, Irkutsk, far to the east of the Jenisei, is only 1330
feet above the level of the sea, or about one third lower than Munich.
If we pass from the differences of temperature manifested in the plains to
the inequalities of the polyhedric form of the surface of our planet, we
shall have to consider mountains either in relation to their influence on
the climate of neighboring
p 327
valleys, or according to the effects of the hyposometrical relations on
their own summits, which often spread into elevated plateaux. The division
of mountains into chains separates the earth's surface into different
basins, which are often narrow and walled in, forming caldron-like valleys,
and (as in Greece and in part of Asia Minor) constitute an individual local
climate with respect to heat, moisture, transparancy of atmosphere, and
frequency of winds and storms. These circumstances have at all times
exercised a powerful influence on the character and cultivation of natural
products, and on the manners and institutions of neighboring nations, and
even on the feelings with which they regard one another. This character of
'geographical individuality' attains its maximum, if we may be allowed so to
speak, in countries where the differences in the configuration of the soil
are the greatest possible, either in a vertical or horizontal direction,
both in relief and in the articulation of the continent. The greatest
contrast to these varieties in the relations of the surface of the earth are
manifested in the Steppes of Northern Asia, the grassy plains (savannahs,
llanos, and pampas) of the New Continent, the heath ('Ericeta') of Europe,
and the sandy and stony deserts of Africa.
The law of the decrease of heat with the increase of elevation at different
latitudes is one of the most important subjects involved in the study of
meteorological processes, of the geography of plants, of the theory of
terrestrial refraction, and of the various hypotheses that relate to the
determination of the height of the atmosphere. In the many mountain
journeys which I have undertaken, both within and without the tropics, the
investigation of this law has always formed a special object of my
researches.*
[footnote] *Humboldt, 'Recueil d'Observations Astronomiques', t. i., p.
126-140; 'Relation Historique', t. i., p. 119, 141, 227; Biot, in
'Connaissance des Temps pour l'an' 1841, p. 90-109.
Since we have acquired a more accurate knowledge of the true relations of
the distribution of heat on the surface of the earth, that is to say, of the
inflections of isothermal and isotheral lines, and their unequal distance
apart in the different eastern and western systems of temperature in Asia,
Central Europe, and North America, we can no longer ask the general
question, what fraction of the mean annual or summer temperature corresponds
to the difference of one degree of geographical latitude, taken in the same
meridian? In each system of 'isothermal' lines of equal curvature there
reigns a
p 328
close and necessary connection between three elements, namely, the decrease
of heat in a vertical direction from below upward, the difference of
temperature for every one degree of geographical latitude, and the
uniformity in the mean temperature of a mountain station, and the latitude
of a point situated at the level of the sea.
In the system of Eastern America, the mean annual temperature from the coast
of Labrador to Boston changes 1.6ºdegrees for every degree of latitude;
from Boston to Charleston about 1.7 degrees; from Charleston to the tropic
of Cancer, in Cuba, the variation is less rapid, being only 1.2 degrees. In
the tropics this diminution is so much greater, that from the Havana to
Cumana the variation is less than 0.4 degrees for every degree of latitude.
The case is quite different in the isothermal system of Central Europe.
Between the parallels of 38 degrees and 71 degrees I found that the decrease
of temperature was very regularly 0.9degrees for every degree of latitude.
But as, on the other hand, in Central Europe the decrease of heat is 1.8
degrees for about every 534 feet of vertical elevation, it follows that a
difference of elevation of about 267 feet corresponds to the difference of
one degree of latitude. The same mean annual temperature as that occurring
at the Convent of St. Bernard, at an elevation of 8173 feet, in lat. 45
degrees 50' should therefore be met with at the level of the sea in lat. 75
degrees 50'.
In that part of the Cordilleras which falls within the tropics, the
observations I made at various heights, at an elevation of upward of 19,000
feet, gave a decrease of 1 degree for every 341 feet; and my friend
Boussingault found, thirty years afterward, as a mean result, 319 feet. By
a comparison of places in the Cordilleras, lying at an equal elevation above
the level of the sea, either on the declivities of the mountains or even on
extensive elevated plateaux, I observed that in the latter there was an
increase in the annual temperature varying from 2.7 degrees to 4.1 degrees.
This difference would be still greater if it were not for the cooling effect
of nocturnal radiation. As the different climates are arranged in
successive strata, the one above the other, from the cacao woods of the
valleys to the region of perpetual snow, and as the temperature in the
tropics varies but little throughout the year, we may form to ourselves a
tolerably correct representation of the climatic relations to which the
inhabitants of the large cities in the Andes are subjected, by comparing
these climates with the temperatures of particular months in the plains of
France and Italy. While
p 329
the heat which prevails daily on the woody shores of the Orinoco exceeds by
7.2 degrees that of the month of August at Palermo, we find, on ascending
the chain of the Andes, at Popayan, at an elevation of 3826 feet, the
temperature of the three summer months of Marseilles; at Quito, at an
elevation of 9541 feet, that of the close of May at Paris; and on the
Paramos, at a height of 11,510 feet, where only stunted Alpine shrubs grow,
though flowers still bloom in abundance, that of the beginning of April at
Paris. The intelligent observer, Peter Martyr de Aughiera, one of the
friends of Christopher Columbus, seems to have been the first who recognized
(in the expedition undertaken by Rodrigo Enrique Colmenares, in October,
1510) that the limit of perpetual snow continues to ascend as we approach
the equator. We read, in the fine work 'De Rebus Oceanicis',* "the River
Gaira comes from a mountain in the Sierra Nevada de Santa Maria, which,
according to the testimony of the companions of Colmenares, is higher than
any other mountain hitherto discovered.
[footnote] *Anglerius, 'De Rebus Oceanicis', Dec. xi., lib. ii., p. 140
(ed. Col., 1574). In the Sierra de Santa Marta, the highest point of which
appears to exceed 19,000 feet (see my 'Relat. Hist.', t. ii., p. 214), there
is a peak that is still called Pico de Gaira.
It must undoubtedly be so if 'it retain snow perpetually' in a zone which is
not more than 10 degrees from the equinoctial line." The lower limit of
perpetual snow, in a given latitude, is the lowest line at which snow
continues during summer, or, in other words, it is the maximum of height to
which the snow-line recedes in the course of the year. But this elevation
must be distinguished from three other phenomena, namely, the annual
fluctuation of the snow-line, the occurrence of sporadic falls of snow, and
the existence of glaciers, which appear to be peculiar to the temperate and
cold zones. This last phenomenon, since Saussure's immortal work on the
Alps, has received much light, in recent times, from the labors of Venetz,
Charpentier, and the intrepid and persevering observer Agassiz.
We know only the 'lower', and not the 'upper' limit of perpetual snow; for
the mountains of the earth do not attain to those ethereal regions of the
rarefied and dry strata of air, in which we may suppose, with Bouguer, that
the vesicles of aqueous vapor are converted into crystals of ice, and thus
rendered perceptible to our organs of sight. The lower limit of snow is
not, however, a mere function of geographical latitude or of mean annual
temperature; nor is it at the equator, or
p 330
even, in the region of the tropics, that this limit attains its greatest
elevation above the level of the sea. The phenomenon of which we are
treating is extremely complicated, depending on the general relations of
temperature and humidity, and on the form of the mountains. On submitting
these relations to the test of special analysis, as we may be permitted to
do from the number of determinations that have recently been made,* we shall
find that the controlling causes are the differences in the temperature of
different seasons of the year; the direction of the prevailing winds and
their relations to this land and sea; the degree of dryness or humitidy in
the upper strata of the air; the absolute thickness of the accumulated
masses of fallen snow; the relation of the s-line to the total height of the
mountain; the relative position of the latter in the chain to which it
belongs, and the steepness of its declivity; the vicinity of either summits
likewise perpetually covered with show; the expansion, position, and
elevation of the plains from which the snow mountain rises as an isolated
peak or as a portion of a chain; whether this plain be part of the
sea-coast, or of the interior of a continent; whether it be covered with
wood or waving grass; and whether, finally, it consist of a dry and rocky
soil, or of a wet and marshy bottom.
[footnote] *See my table of the height of the line of perpetual snow, in
both hemispheres, from 71 degrees 15' north lat. to 53 degrees 54' south
lat., in my 'Asie Centrale', t. iii., p. 360.