On the Principal Causes of the Difference of Temperature on the Globe.

By Baron Alexander Von Humboldt.

Extract from a public Lecture delivered in the Royal Academy at Berlin, on the 3d of July 1827.

The distribution of heat over the globe, has for many years formed one of the principal objects of my researches.

This subject is intimately connected with the local differences of the productions of nature, with the agriculture and the commercial intercourse of nations, and even, in several respects, with their moral and political situation.

The time is past when we were satisfied with some undefined views on the difference of geographical and physical climates, and when all the modifications of temperature were ascribed either to the shelter afforded by ridges of mountains, or to the various elevations of the surface of the earth.

We have seen, that the remarkable differences of climates which we perceive in large tracts of country, under the same latitude, and on the same level above the surface of the sea, do not arise from the trifling influence of individual localities, but that they are subject to general laws, determined by the form of the continents in general, by their outlines, by the state of their surface, but particularly by their respective positions, and the proportion of their size, to the neighbouring seas.

The relative position of the transparent and opaque, of the fluid or solid parts of the earth, modifies the absorption of the solar rays falling under the same angles, and at the same time the production of heat.

These circumstances, the winter cover of ice and snow, which is peculiar to the continents, and to a very small part only of the seas; the slowness with which large masses of water are heated and cooled; the radiation from smooth or rough surfaces, towards a cloudless sky; the regular currents of the ocean and of the atmosphere, by which water and air from different latitudes and different depths and heights are mixed; all concur to produce the peculiarities of climate.

It may therefore be said, that every place has a double climate, one depending on general and remote causes, on the general position and shape of the continents, and another determined by the peculiar relations of its locality.

Since the problem of the geographical distribution of heat has been considered upon general principles, meteorological observations have been conducted in a more efficient manner.

A smaller number of them now lead to certain results; and the discoveries made within the last twenty years, in the most remote parts of the globe, have gradually enlarged the point of view.

Physical and geological inquiries have now become equally important objects of all extensive voyages and travels.

To begin with the extreme north, I shall here, in the first place, mention a man, whom the dangerous and troublesome occupations of whale-fishing, which were the object of his voyage, have not prevented from carrying on the most refined meteorological and zoological observations.

Captain Scoresby has, for the first time, determined the mean atmospheric temperature of the Polar Seas, which he has taken between the volcanic Island of Jan Mayen, and that part of East Greenland discovered by himself.

In endeavouring to discover a northwest passage, the English government has succeeded in affording to geography, to climatology, and to the theory of magnetism, services which were originally promised to the commercial interest of nations.

Parry, Sabine, and Franklin have, for several years, been employed in investigating the temperature of the atmosphere, and of the sea, in the polar regions; they have penerated to Port Bowen and Melville's Island, consequently nearly to 75° N. Lat.; and they have, in this arduous task, displayed a perseverance, of which we find hardly a parallel instance in the history of human exertions and struggles against the elements.

Captain Weddell has recently destroyed the ancient prejudice, sanctioned by Cook's illustrious name, that the South Pole is, on account of a more extended mass of ice, less accessible than the North Pole.

The discovery of a new archipelago to the SSE. of Terra del Fuego, has led to an expedition in which Captain Weddell found a sea completely free from ice, under the 74° Lat. (far beyond two solitary islands discovered by the Russian Captain Billinghausen.)

In turning to the temperate zone, we find a great many points where the average temperature, which hitherto was considered to be invariable, has been measured.

Various astronomers in New Holland, and on the foot of the Indian Himalaya, Catholic and Protestant missionaries at Macao, in Van Diemen's Land, and in the Sandwich Islands, have furnished us with new facts towards comparing the northern and southern, the eastern and western hemispheres, in the torrid and temperate zones, consequently those parts of the globe which are most abundant in water, as well as those which are most abundant in land.

In the same manner, the proportion of heat under the line, and in both the tropics, has been determined.

These points, as ascertained in numbers, are particularly important as fixed points, because they may, like the zone of the warmest sea-water, (between 84° and 87° Fah.; 23° and 24° 5' R.), in future ages serve to determine the much disputed variability of the temperature of our planet.

It is necessary to mention here, that we have been long in want of climatological determinations in the most southern parts of the temperate zones, between the 28° and 30° lat.

This part of the world forms as it were an intermediate link between the climate of Palms, and that region in which, according to the tradition of the east, mankind, along the Mediterranean, in Asia Minor, and Persia, first awoke to intellectual developement, to mild manners, and to taste in the cultivation of the arts.

The observations of Niebuhr, Nouet, and Coutel in Egypt, those of my unfortunate friend Ritchie in the Oasis of Murzuk, could, on account of local circumstances, only lead to erroneous results.

The large and classical work on the Canary Islands, for which we are indebted to Mr Leopold Von Buch, has now also filled up this blank, in the same way as his travels in Lapland and to the most northern promontory of Europe, first furnished us with a clear illustration of the causes which, in the Scandinavian peninsula, beyond the polar circle, diminish the severity of the winter cold, and preserve to the springs the temperature which they had received from deeply seated strata, and which occasion, under the influence of a continental climate and that of the coast, an unequal elevation of the snow line, and of the upper limit at which different species of trees grow.

If we follow the current of the sea, which traverses the great valley of the Atlantic Ocean, from east to west, we find almost unexpectedly rich sources of instruction in the New World, from Russian America, and the settlements of the Canadian hunters, to the River La Plata, and the most southern parts of Chili.

It is no longer foreign naturalists who communicate to us the notices they have been able to collect during a short residence in plains, rich in wood and grass, and on the ice-covered ridges of the Cordillera; we have no longer need to judge of the mean temperature of the whole year by that of single months or weeks; here we obtain every where solid and complete information from the inhabitants themselves.

The executive power of the United States of North America has ordered meteorological observations for five years to be made three times a day, at seventeen different points, occupied by military garrisons, between the 28° and 47° lat., between the Missouri and the Alleghanys, the lake Michigan, and the coast of Pensacola; and from these observations, the average temperature of days, months, and of the whole year, is drawn.

These observations calculated by Mr Lovell, surgeon-general of the army, have been published at the expense of the American government, and have been distributed to all scientific institutions in Europe.

If this excellent example was followed in the eastern part of our continent, and if, by the command and at the expence of a powerful monarch, similar comparative theometrical observations were carried on in well selected points in the extensive district situated between the Vistula and the Lena, the whole science of climate would in a few years appear in a new and much improved form.

The zeal by which the United States of North America are animated, has arisen equally strong in the lately emancipated Spanish America.

Journals, printed 9,000 feet above the level of the sea, give daily the height of the thermometer, barometer, and hygrometer, taken with very exact instruments, made at Paris and London, in the enormous extent from the 28° N. to the 40° S. lat. Thus the political revolution of these countries has not only improved their own condition and the industry of Europe, but it will also, when the population increases, and scientific knowledge spreads, over so many mountains and elevated plains, lead to a better knowledge of the higher regions of the atmosphere.

In those countries, whole provinces rise like islands in an ocean of air, to the height of Etna, or the Peak of Teneriffe: in the old continent, where the travelling naturalist erects his tent near the line of permanent snow, populous towns are found in America.

In modern times Africa, which the ancients represented upon coins and monuments as the kingdom of palms, has been found rather deficient in this tribe of trees; and, in the same manner, later travellers have modified in a singular manner the belief in the constant uniform tropical heat of the African deserts.

In the Oasis of Murzuk in Fezzan, Ritchie and Lyon found, during several summer months, the thermometer in the shade, at from 5 to 6 feet above the ground, to indicate 86° to 91° Fahr. (24° to 26° R.), at 5 o'clock in the morning, and from 118° to 129° Fahr. (38° to 43° R.) at noon, a temperature which probably arose from the radiation produced by the sand floating in the air; and, in the same place, Dr Oudney died of cold in the end of December.

This spot is situated in the centre of Africa, on the frontiers of Bornou, under the 13th degree of lat., and, according to barometrical measurement is not 1200 feet above the level of the sea.

It is said that the water in the leather bottles, which Oudney's caravan carried along with them, was frozen this same night.

But Major Denham, Clapperton's companion, whom I desired, after his return from the lake Tchad, to give me some oral explanation, told me, that, in the morning, some hours after Dr Oudney's death, the temperature of the air was not below 49° Fahr.

(7 [Formel] ° R.).

In South America, at a less distance from the equator, near Bogota and Quito, I saw the water free from ice, at the height of 8500 and 9000 feet, notwithstanding the strong effect of the radiation of high plains in producing cold.

In the manuscripts of young Beaufort, who died lately in Upper Senegal, a victim to scientific zeal, I find that under the 16th degree of latitude, the thermometer marked in the shade on the same day 113° Fahr. (36° R.) at noon, and 59° Fahr. (12° R.) early in the morning.

The temperature of the air in the plains of America never sinks so low in the same northern latitude.

In laying before the Academy last year, a detailed account of the excellent labours of Ehrenberg and Hemperich, I have already mentioned the cold to which these learned travellers were exposed, when in the Desert of Dongola under the 19th degree of latitude.

North winds penetrated into this southern tropical country, and, in December, the thermometer sunk to 38° Fahr.

(2° 5' R.) above the freezing point, consequently 12° of R. lower than it had ever been observed, under the same latitude, in the West Indies, according to the accounts carefully collected by myself.

It is astonishing to find Africa in its deserts colder than America, with all its rich vegetation, and this not on the margin of the tropics, but at the very centre of them.

The true causes of this singular cooling process have not yet been sufficiently explained.

Perhaps it is the radiation of heat from the soil through the dry air towards a cloudless sky, or a sudden expansion produced by the pouring of humid strata into this dry air, and the descent of the upper parts of the atmosphere.

It is generally known that more than two-thirds of our planet are covered by a body of water, which, by its contact with the atmosphere, exercises the most powerful influence upon the climate of the continents.

The rays from the sun produce heat according to different laws, as they fall either upon the water or upon the solid surface of the earth.

The mobility of the particles of which we imagine fluid bodies to be composed, produces currents and an unequal distribution of temperature; cooled and condensed by radiation, the particles of water sink to the bottom.

By ascending in balloons, climbing upon insulated peaks of mountains, by thermoscopic apparatus sunk into the sea, it has been possible to determine the velocity of the cooling process which takes place at different seasons, from below upwards, in the atmosphere, and from above downwards, in the occean, and in fresh water lakes.

The animals, therefore, which dwell in both these elements, find on each point of the globe, in the aeriform and liquid elements, the most heterogeneous climates, placed in strata one above another.

In the depth of the sea, under the Line, and in alpine lakes of the temperate zone, there is always a fixed degree of cold, viz. that degree at which the water attains the greatest density.

The experiments of Ellis, Forster and Saussure, have been repeated under all zones and in all depths; but what we know of the lowest temperature of the air, and of seawater, as well as of the greatest effect of the radiation of heat between the tropics, serves as an infallible proof that the cold which there exists near the bottom of the sea, is produced by a current which, in the depths of the ocean, passes from the poles towards the equator, and cools the inferior strata of water in the southern ocean, like the current of air in the upper atmosphere, which moves from the equator to the poles, to temper the cold of the winter in the northern regions.

The immortal Benjamin Franklin first taught us that sandbanks are sooner recognised by the thermometer than by the sounding line.

They are islands of the submarine land, which the elastic subterranean powers had not been able to elevate above the surface of the water.

On the declivity of the shoals, the inferior and colder strata ascending by impulse, are mixed with the upper and warmer ones; and thus the sudden cold of the sea-water shews to the navigator that danger is near.

The shallows, by their temperature, act on the air above them, in which they produce fogs and groups of clouds, which are perceived at a great distance.

Before more extensive investigations had been made on the distribution of heat over the globe, it was believed that the climate of two places could be determined by the extremes of the temperature in summer and winter.

This view of things has still been preserved in popular opinion, whilst naturalists have long ago renounced it as erroneous; for, although undoubtedly the extremes of single days and nights are in a certain proportion to the mean temperature of the year, yet the distribution of heat in the different seasons is strikingly different, although the mean annual temperature be one and the same,--a circumstance which has a very great influence on the growth of plants and on the health of man. I have endeavoured to determine the law of this distribution, according to different situations and heights.

But comparative results in numbers ought to contain the mean temperature of every month, derived from the two extremes of every day, supposing an arithmetical series to be formed.

This method was first adopted by Reaumur in 1735: he compared the produce of two harvests, not (like Herschel) with the numbers and size of the spots in the sun, but with the quantity of heat which the corn received in the time of vegetation.

Many labours have of late been directed towards ascertaining the hour, the mean temperature of which expresses also that of the whole year.

I here only mention the observations carried on in Scotland at Leith Fort.

The night watch of a military post has been employed for establishing observations of the thermometer during two years, from hour to hour; and from the mass of these observations, which ought to be repeated in other latitudes, it has been calculated, that, in the latitude of Edinburgh, a single daily observation at 9 o'clock 13 minutes in the morning, and in the evening at 8 o'clock 29 minutes, would be sufficient to fix the average heat of the year . Of the months, it is April and October which give this important result (a fact, first discovered by Leopold von Buch, which is connected with remarkable modifications of the upper currents of the atmosphere), except when, as in the island of Grand Canary, local causes carry the maximum of heat to a later period, and place it in October.

A result, which does not differ from the true by one-half degree of Reaumur's thermometer, is also obtained by the mean of two hours of the same denomination.--Results of the Thermometrical Observations made at Leith Fort every hour of the day and night during the years 1824 and 1825, p. 19.

If I frequently allude to the great increase of meteorological observations within the last twenty years, I by no means wish to express an opinion that the perfection of climatology is particularly founded on such an increase.

Here, as in all collections of knowledge derived from experiments, which are too soon denominated sciences, every thing depends on "an accurate conception of nature," and a just view of the consequences to be drawn from well-arranged facts.

If we attempt to conceive the problem of the distribution of temperature in its most general sense, we may imagine the planetary heat either (as in the present oxydised, hardened surface of the earth) to be a consequence of the position in relation to a central body, which excites heat; or (as in the first state of the condensation of matter dissolved in the form of vapour) the consequence of internal processes of oxidation, precipitation, change of capacity, or electro-magnetic currents.

Many geognostical phenomena, which I have mentioned in another paper, seem to indicate such a developement of internal heat, produced by our planet itself.

Moreover, the doubts raised against the peculiar heat in mines in both parts of the world, have been entirely removed by recent experiments of an ingenious astronomer M. Arago, on water rising up through deep borings in what are called Artesian Wells.

The greater the depth from which the water ascends, the warmer it has been found.

In this case, there can be no suspicion of strata of air sinking down and being condensed, and consequently disengaging heat; nor can the neighbourhood of men, or of the lanterns of miners, exercise an influence in this case.

The waters carry along with them the heat which they have acquired by a long continued contact with rocky masses at different depths.

These important observations shew how, independently of the obliquity of the ecliptic in the earliest, and, as it were, youthful state of our planet, the tropical temperature and tropical vegetation could arise under every zone, and continue, till, by the radiation of heat from the hardened surface of the earth, and by the gradual filling up of the veins with heterogeneous minerals a state was formed, in which (as Fourier has shewn in a profound mathematical work) the heat of the surface, and of the atmosphere, depends merely upon the position of the planet towards a central body, the sun.

We gladly resign to other natural philosophers the task to decide, how deep below the oxidised and hardened surface of the earth the melted fluid masses lie, which are poured out through the apertures of volcanoes, which periodically agitate the continents and the bottom of the ocean, and force hot mineral springs upwards through clefts in granite and porphyry.

The depth of our mines is too inconsiderable to enable us, from the unequal increase of temperature which has been hitherto observed in them, to give the satisfactory numerical solution of a problem which occupies the curiosity of men who live, as it were, upon a vault of rocks.

Suffice it here to point out how the recent views of geologists have revived the old mythus of Pyroplegeton and of Hephastos.

When a planet is everywhere surrounded by aerial strata, and when the oxidised surface of the earth, with its clefts almost everywhere closed or filled up, by a long radiation of heat, has arrived at a state of equilibrium between receiving and losing, in such a manner that its external temperature and the difference of climates arise solely from its position towards the sun, towards a larger central body which is perpetually generating light, then the problem of the temperature of any place in its most general form, may be considered as dependent solely upon the manner in which the influence of the meridian height of the sun manifests itself.

This height determines, at the same time, the magnitude of the semidiurnal circles, the density of the aerial strata, through which the rays of the sun pass, before they arrive at the horizon; it also determines the quantity of the absorbed or calorific rays (a quantity which rapidly increases with the size of the angle of incidence); and, lastly, the number of the rays of the sun, which, mathematically considered, a given horizon receives.

The production of heat, as far as a greater or less is concerned, can accordingly be considered as proceeding from the illuminated surface of the earth.

The absorption which the rays of the sun undergo in their passage through the atmosphere, or (to express it in another manner) the production of heat by the diminution of light is extremely small; but nevertheless is perceptible on the ocean, where, at a great distance from the coast, and even when the water was colder than the atmosphere, I observed the temperature of the latter increasing at noon with the height of the sun .

Mr Arago has first called my attention to this remarkable effect of the absorption of light in the atmosphere.--Con. des Tems pour 1828, p. 225.

Recent researches have shewn, that, in both continents, under the equator, where the mean temperature rises to 82° Fahr. (22°.2 R.) it is not much warmer than it is in 10° north and south latitude.

According to the Commentary of Geminus on the Astronomical Poem of Aratus , some Greek philosophers believed the temperature of the tropics even to surpass that of the equator. M.

Arago has, in a very ingenious manner, demonstrated, by numerous optical experiments, that, from the vertical incidence to a zenith distance of 20°, the quantity of the reflected light (and the lesser heating of the illuminated body depends on this quantity), remains almost the same.

In comparing the mean annual temperatures with one another, I find, that, in the western part of the old continent, the temperatures diminish from the south towards the north in the following proportion:

Essai Politique sur l'Isle de Cuba, 1826, t. ii. p. 79-92. where I think I have obviated the doubts raised by Mr Atkinson.--Mem. of the Astron. Soc. vol. ii. p. 137, 137.

Esig. in Aratum eays.

13. Strabo, Geogr. lib. ii. p. 97.

In the eastern parts of the new continent, the diminutions of the mean temperature are as follows:

From 20° to 30° Latitude, 5° Reaum.

3040 5 .7 4050 7 .2 5060 5 .8

From 20° to 30° north Latitude.

3°.2 Reaum.

3040 3 .6 4050 5 .7 5060 4 .4

In both the continents, the region where the diminution of heat is most rapid, is to be found between 40° and 45° latitude.

In this result, the observation agrees in a remarkable manner with the theory; for the variation of the square of the cosines which expresses the law of the mean temperature, is largest at 45° latitude.

This circumstance, as I have shown in another place, has exercised a very beneficial influence on the state of civilisation of those nations who live in the mild countries, under this, the medium parallel of latitude.

There the district where the vine grows, borders upon that of the olive and orange tree.

Nowhere else upon earth (in proceeding from the north to the south) does the heat increase more rapidly with the geographical latitude; nowhere else do the various vegetable productions, used in gardening and in agriculture, succeed each other more rapidly.

This variety animates industry and the commercial intercourse of nations.

We may here state that partial, daily, and monthly changes of temperature are, on account of the motion of the atmosphere, produced by the transportation of colder or warmer strata, by greater or less electric tension, by the formation of clouds or the diffusion of vapours; in short, by an almost infinite number of variable causes, acting at a greater or smaller distance.

The study of meteorology has, unfortunately, begun in a zone where the causes are most complicated, and the number and intensity of the disturbing powers greatest.

If ever civilization, as may now be expected, shall establish one of its principal seats in the tropics, it is to be presumed that these phenomena, which are so simple there, will be more easily ascertained than in our climates, where the play of many conflicting causes has so long concealed them from our view.

From that which is simple it is easy to proceed to what is complicated, and we may imagine a scientific meteorology as returning from the tropics to the north.

In the climate of palms, a feeble east wind always brings strata of air along with it, having generally the same temperature.

The barometer shows, like the progress of the needle, the hour of the day.

Earthquakes, tempests, and thunder-storms do not disturb the small but periodical tides of the atmosphere.

The changed declination of the sun, together with the upper currents of the air, from the equator towards the pole, modified by this declination, determine the beginning of the rainy season and the electric explosions, which both begin at regular periods.

The traveller may know his way almost as well by the direction of the clouds as by the compass; and, in the dry season, the appearance of a cloud on the deep blue sky would, in many districts of the tropics, astonish the natives as much as the fall of an aerolite or of the red polar snow would do us; or as the crash of thunder in Peru; or, in the tropical plains, a hail storm.

This simplicity and regularity in the meteorological phenomena allow us to expect an easier and more favourable insight into the relation of their causes.

As long as the observations on the magnetic inclination, declination and intensity of forces, remained dispersed in the reports of travellers, and had not been united by magnetical lines, the doctrine of the distribution of magnetism on the earth could not be expected to make any important progress.

Supported by analogy, it has been attempted to simplify by a careful employment of well ascertained facts, the complicated doctrine of the distribution of heat.

Places having an equal mean temperature of the year, of summer, or of winter, have been connected with one another by curves.

This was the origin of the system of isothermal lines , of which I published a full account in the year 1817.

They descend towards the equator, because in Eastern Asia and the eastern parts of North America we find, on an equal level above the sea, and in a more southern latitude, the same temperature which we meet with in the centre of Europe, in a more northern latitude.

The remarkable circumstance, that the highest civilization of the species to which we belong has developed itself, almost under the same latitudes in the temperate zone upon two opposite coasts, the eastern coast of the new and the western of the old continent, must early call our attention to the difference of heat under the same latitudes.

The question arose by how many thermometrical degrees the old world was warmer than the new, and it is not long since it was known, that the isothermal lines from the latitude of Florida to that of Labrador, do not run parallel, and that the eastern and western coasts of North America are almost as different from one another as those of Western Europe and of Eastern Asia.

The shape and grouping of the continents, and their relation to the neighbouring seas, are the principal causes which determine the inflection of the isothermal lines, or the direction of equally warm zones, into which we may conceive the whole globe to be divided.

The predominance of west winds in the temperate and cold regions determines the difference of climates on the eastern and western coasts of one and the same continent.

The western winds, which are considered as reactions of the tropical tradewinds reach an eastern coast, after having traversed in winter a continent covered with snow and ice; to the western coasts, on the contrary (in Europe as well as in New California and Nootka), western winds carry strata of air, which even in the severest winter have been heated by contact with the vast surface of the ocean.

Led by these ideas, I have considered it of importance to obtain a knowledge of the lowest temperature to which the Atlantic sinks, out of the Gulf Stream, between 40° and 50° north latitude (consequently in the latitudes of Spain, France and Germany). I have found that, in the month of January, in 40° latitude, the water of the sea does not sink below 56° Fahr. (10°.7 R.) and in 45° latitude not below 54° Fahr.

(9°.8 R.)

The much esteemed geographer of India.

Major Rennel, who for thirty years has been employed in studying the direction of the currents of the Atlantic, and who, during my last visit to England, communicated to me a part of his manuscript materials, has, in 50° latitude, consequently in the zone of the north of Germany, observed in winter a temperature of the sea-water, to which the atmosphere does not reach in the month of January, even in the mild climate of Marseilles.

If the relative extent of Asia and North America, of the Pacific and the Northern Atlantic, was different from what it is, the whole system of winds in the northern hemisphere, would, by the unequal heating of the solid, as well as of the fluid, parts of the surface of the earth, be changed in their direction as well as in their intensity.

De la Distribution de la Chaleur sur le Globe.--Mem. de la Societe d'Arcueil, t. iii.

Europe is indebted for its milder climate to its position on the globe (the position in which it stands in regard to the neighbouring seas) and to its peculiar form. Europe is the western part of the old continent; and consequently the great Atlantic Ocean, which already in itself has the power of diminishing the cold, and which is besides partly warmed by the Gulf Stream, lies to the west of it.

That part of the world which of all others enjoys the greatest share of a tropical climate, the sandy Africa, is so situate that Europe is heated by the strata of air, which, ascending from Africa, move from the Equator towards the North Pole.

Had the Mediterranean not existed, the influence of Africa on the temperature and the geographical distribution of plants and animals in Europe, would have been still more considerable.

The third principal cause of the milder climate of Europe is, that this part of the world does not approach the North Pole nearly as much as America and Asia do; and that, on the contrary, it lies opposite the greatest extent of sea-water, free from ice, which is known in the whole polar zone.

The coldest points of the earth, which have lately been improperly called Poles of Cold, do not coincide with the magnetic poles, as Dr Brewster has endeavoured to prove in the English version of my paper on the Isothermal Lines.

According to Captain Sabine's researches, the minimum of the annual mean temperature on the surface of the earth, is to the NW.

of Melville's Island, in the meridian of Behring's Straits, probably in 82° to 83° north Lat.

The summer boundary of the ice, which, between Spitzbergen and East Greenland, recedes to 80° and 81° north Lat., is in about 75° N. Lat., every where between Nova Zembla, the Bone Islands of New Siberia and Icey Cape, the most western cape of America.

Even the winter boundary of ice, the line on which the ice approaches the nearest to our continent, scarcely surrounds Bear Island.

From the North Cape, which is heated by a southwestern current of the sea, the navigation to the most southern promontory of Spitzbergen is never interrupted, not even in the most severe winters.

The polar ice diminishes in quantity wherever it finds an opening to flow out, as in Baffin's Bay, and between Iceland and Spitzbergen.

The situation of the Atlantic Ocean exerts a most beneficial influence on the existence of that sea-water, free from ice, in the meridian of East Greenland and Spitzbergen, which has so important an influence upon the climate of the north of Europe.

On the other hand, the icebergs, which are driven from Baffin's Bay and Barrow's Straits to the south, accumulate in that large mediterranean sea, which geographers designate by the name of Hudson's Bay.

This accumulation of ice increases the cold of the neighbouring continent so much, that, as reported by Captain Franklin in his latest MS., in York Factory, and at the mouth of Hayes River, which lie in the same latitudes as the north of Prussia and Courland, in digging wells, ice is found everywhere at the depth of four feet.

The most northern and most southern boundaries of the fixed polar ice, that is, the summer and winter boundaries, on the situation of which the temperature of the northern continents depends, seem to have changed but little, as far as historical records go; which fact has been recently confirmed by careful inquiries.

The injurious influence which small isolated masses of ice, driven sometimes by currents into the neighbourhood of the Azores, exercise, as it is said, upon the continent of Europe, is one of those tales, first derived from philosophers, and received by the vulgar, after the former have long ceased to believe in them.

In the same latitudes, where, in the north of Europe, agriculture and gardening are carried on, we find in North America and North Asia only marshes and tracts of land covered with mosses: in the interior of Asia, on the other hand, the powerful radiation of heat, between the almost parallel chains of the Himalaya, the Zungling and the Himmelsgebirge, (a country on which Klaproth's geographical researches have thrown great light), exercises the most beneficial influence on the Asiatic population.

The line of permanent snow, on the northern declivity of the Himalaya, lies 4000 feet higher than on the southern; and the physical explanation which I have given of this singular phenomenon , has, according to a report of Mr Colebrooke, been confirmed by recent measurements and observations in the East Indies.

Millions of men of Thibetian origin, of a gloomy religious cast of mind, occupy populous towns, in a country where fields and towns would, during the whole year, be buried in deep snow, if this high table-land was less extensive and less continuous.

Annales de Chimie et de Physique, tom. iii. p. 297; tom. ix. p. 310; tom. xiv. p. 5.

As the currents of the atmosphere are modified in many different manners, by changes in the declination of the sun, and by the direction of the chains of mountains on the declivities of which they descend, the currents, also, of the liquid ocean carry the warmer waters of the lower degrees of latitude into the temperate zone.

I need not here mention how the waters of the Atlantic, always moved in the same direction by the trade-winds, are carried against the dike formed by the isthmus of Nicaragua, then turn to the north, make the round of the Gulf of Mexico, flow out through the Channel of the Bahamas, proceed as a current of warm water to the north-east towards the banks of Newfoundland, then to the south-east, towards the group of the Azores; and, when favoured by the north-west wind, carry along with them the fruits of palm trees from the Antilles; casks of French wines from wrecked ships; nay, even living Esquimaux in their leather boats from East Greenland, which they cast on the coasts of Ireland, of the Hebrides, or of Norway.

A travelled astronomer, Captain Sabine, who, after returning from the Polar Regions, performed experiments with the pendulum in the Gulf of Guinea, on the African Island of St Thomas, informed me, how casks of palm oil, which had been lost by shipwreck at Cape Lopez, a little south of the Equator, were carried onwards, first by the equatorial current, and then by the Gulf Stream, crossing the Atlantic twice, from east to west, and from west to east, between 3° and 50° N. Lat., safely arrived on the coasts of Scotland.

The well preserved mark of the African proprietors left no doubt as to the direction the casks had taken.

In the same manner, as in this case, the equatorial waters in the Atlantic are carried north by the Gulf Stream, I have, in the Pacific, in its southern hemisphere, observed a current (along the coasts of Chili and Peru), which carries colder water from higher latitudes to the Tropics.

In this current I saw the thermometer, in the port of Truxillo, in the month of September, fall to 61° Fahr. (12°.8 R.) and in the port of Callao, near Lima, at the end of November, to 60° Fahr. (12°.4 R.) A distinguished young officer of the Danish navy, Baron Dirckinck von Holmfeldt, has, at my request, at different seasons of the year 1825, observed this singular phenomenon, to which for so long a time no attention had been paid.

Making use of thermometers, carefully compared by Mr Gay Lussac and myself, he again found the water of the sea, in the port of Callao, in August 60 [Formel] ° Fahr. (12°.6 R.) and in March 67 [Formel] ° Fahr. (15°.7 R.)

Whilst, out of the current, at the promontory of Parina, the calm sea, as usually in those latitudes, showed the great heat of 79 [Formel] ° to 81°.5 (21° to 22° R.)

We cannot, in this place, explain how this stream of colder water, which increases the difficulty of the southern navigation from Guayaquil to Peru, and from Peru to Chili, is for some months modified in its temperature by the Garua, i. e. the vapours which constantly veil the sun; and how it renders the climate of the plains of Peru cooler.

As all human attempts to arrive at a scientific view of the phenomena of nature can have for their final object only a clear conception of our own nature, thus the investigation, with the principal topics of which we have now been occupied, at last leads us to consider, how the differences of climate manifest themselves in the character, in the civilization, and, perhaps, even in the development of the language of different tribes of the human race.

This is the point where the important doctrine of the distribution of heat over the globe comes to be connected with the history of mankind, and beyond which it ceases to be an object of purely physical inquiry.