Digitale Ausgabe

The distribution of heat over the globe, has for many yearsformed one of the principal objects of my researches. This sub-ject is intimately connected with the local differences of the pro-ductions of nature, with the agriculture and the commercial in-tercourse of nations, and even, in several respects, with their mo-ral and political situation. The time is past when we were satis-fied with some undefined views on the difference of geographicaland physical climates, and when all the modifications of tempera-ture were ascribed either to the shelter afforded by ridges ofmountains, or to the various elevations of the surface of theearth. We have seen, that the remarkable differences ofclimates which we perceive in large tracts of country, under thesame latitude, and on the same level above the surface of thesea, do not arise from the trifling influence of individual locali-ties, but that they are subject to general laws, determined by theform of the continents in general, by their outlines, by the stateof their surface, but particularly by their respective positions,and the proportion of their size, to the neighbouring seas. The

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* Extract from a public Lecture delivered in the Royal Academy at Berlin,on the 3d of July 1827.|330| relative position of the transparent and opaque, of the fluid orsolid parts of the earth, modifies the absorption of the solar raysfalling under the same angles, and at the same time the produc-tion of heat. These circumstances, the winter cover of ice andsnow, which is peculiar to the continents, and to a very smallpart only of the seas; the slowness with which large masses of wa-ter are heated and cooled; the radiation from smooth or roughsurfaces, towards a cloudless sky; the regular currents of theocean and of the atmosphere, by which water and air from dif-ferent latitudes and different depths and heights are mixed; allconcur to produce the peculiarities of climate. It may thereforebe said, that every place has a double climate, one depending ongeneral and remote causes, on the general position and shape ofthe continents, and another determined by the peculiar relationsof its locality. Since the problem of the geographical distribution of heat hasbeen considered upon general principles, meteorological ob-servations have been conducted in a more efficient manner.A smaller number of them now lead to certain results; andthe discoveries made within the last twenty years, in the mostremote parts of the globe, have gradually enlarged the pointof view. Physical and geological inquiries have now becomeequally important objects of all extensive voyages and tra-vels. To begin with the extreme north, I shall here, in thefirst place, mention a man, whom the dangerous and trouble-some occupations of whale-fishing, which were the object of hisvoyage, have not prevented from carrying on the most refinedmeteorological and zoological observations. Captain Scoresbyhas, for the first time, determined the mean atmospheric tem-perature of the Polar Seas, which he has taken between thevolcanic Island of Jan Mayen, and that part of East Greenlanddiscovered by himself. In endeavouring to discover a north-west passage, the English government has succeeded in affordingto geography, to climatology, and to the theory of magnetism,services which were originally promised to the commercial inte-rest of nations. Parry, Sabine, and Franklin have, for severalyears, been employed in investigating the temperature of the at-mosphere, and of the sea, in the polar regions; they have pene-rated to Port Bowen and Melville’s Island, consequently nearly to|331| 75° N. Lat.; and they have, in this arduous task, displayed aperseverance, of which we find hardly a parallel instance in thehistory 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, onaccount of a more extended mass of ice, less accessible than theNorth Pole. The discovery of a new archipelago to the SSE.of Terra del Fuego, has led to an expedition in which CaptainWeddell found a sea completely free from ice, under the 74°Lat. (far beyond two solitary islands discovered by the RussianCaptain Billinghausen.) In turning to the temperate zone, we find a great many pointswhere the average temperature, which hitherto was considered tobe invariable, has been measured. Various astronomers in NewHolland, and on the foot of the Indian Himalaya, Catholic andProtestant missionaries at Macao, in Van Diemen’s Land, and inthe Sandwich Islands, have furnished us with new facts towardscomparing the northern and southern, the eastern and westernhemispheres, in the torrid and temperate zones, consequentlythose parts of the globe which are most abundant in water, aswell as those which are most abundant in land. In the samemanner, the proportion of heat under the line, and in both thetropics, has been determined. These points, as ascertained innumbers, are particularly important as fixed points, because theymay, like the zone of the warmest sea-water, (between 84° and87° Fah.; 23° and 24° 5′ R.), in future ages serve to determinethe much disputed variability of the temperature of our planet. It is necessary to mention here, that we have been long inwant of climatological determinations in the most southern partsof the temperate zones, between the 28° and 30° lat. This partof the world forms as it were an intermediate link between theclimate of Palms, and that region in which, according to thetradition of the east, mankind, along the Mediterranean, inAsia Minor, and Persia, first awoke to intellectual develope-ment, to mild manners, and to taste in the cultivation of thearts. The observations of Niebuhr, Nouet, and Coutel inEgypt, those of my unfortunate friend Ritchie in the Oasis ofMurzuk, could, on account of local circumstances, only lead to|332| erroneous results. The large and classical work on the CanaryIslands, for which we are indebted to Mr Leopold Von Buch,has now also filled up this blank, in the same way as his travelsin 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, diminishthe severity of the winter cold, and preserve to the springs thetemperature which they had received from deeply seated strata,and which occasion, under the influence of a continental climateand that of the coast, an unequal elevation of the snow line, andof the upper limit at which different species of trees grow. If we follow the current of the sea, which traverses thegreat valley of the Atlantic Ocean, from east to west, we findalmost unexpectedly rich sources of instruction in the NewWorld, from Russian America, and the settlements of theCanadian hunters, to the River La Plata, and the most southernparts of Chili. It is no longer foreign naturalists who commu-nicate to us the notices they have been able to collect during ashort residence in plains, rich in wood and grass, and on theice-covered ridges of the Cordillera; we have no longer need tojudge of the mean temperature of the whole year by that ofsingle months or weeks; here we obtain every where solid andcomplete information from the inhabitants themselves. The executive power of the United States of North Americahas ordered meteorological observations for five years to be madethree times a day, at seventeen different points, occupied by mi-litary garrisons, between the 28° and 47° lat., between the Mis-souri and the Alleghanys, the lake Michigan, and the coast of Pen-sacola; and from these observations, the average temperature ofdays, months, and of the whole year, is drawn. These obser-vations calculated by Mr Lovell, surgeon-general of the army,have been published at the expense of the American govern-ment, and have been distributed to all scientific institutions inEurope. If this excellent example was followed in the easternpart of our continent, and if, by the command and at the ex-pence of a powerful monarch, similar comparative theometricalobservations were carried on in well selected points in the ex-tensive district situated between the Vistula and the Lena, the|333| whole science of climate would in a few years appear in a newand much improved form. The zeal by which the United States of North America areanimated, has arisen equally strong in the lately emancipatedSpanish America. Journals, printed 9,000 feet above the levelof the sea, give daily the height of the thermometer, barometer,and hygrometer, taken with very exact instruments, made atParis and London, in the enormous extent from the 28° N. tothe 40° S. lat. Thus the political revolution of these countrieshas not only improved their own condition and the industry ofEurope, but it will also, when the population increases, andscientific knowledge spreads, over so many mountains and ele-vated plains, lead to a better knowledge of the higher regions ofthe atmosphere. In those countries, whole provinces rise likeislands in an ocean of air, to the height of Etna, or the Peakof Teneriffe: in the old continent, where the travelling natu-ralist erects his tent near the line of permanent snow, populoustowns are found in America. In modern times Africa, which the ancients represented uponcoins and monuments as the kingdom of palms, has been foundrather deficient in this tribe of trees; and, in the same manner,later travellers have modified in a singular manner the be-lief in the constant uniform tropical heat of the African de-serts. In the Oasis of Murzuk in Fezzan, Ritchie and Lyonfound, during several summer months, the thermometer in theshade, 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 from118° to 129° Fahr. (38° to 43° R.) at noon, a temperature whichprobably arose from the radiation produced by the sand floatingin the air; and, in the same place, Dr Oudney died of cold inthe end of December. This spot is situated in the centre of Af-rica, on the frontiers of Bornou, under the 13th degree of lat., and,according to barometrical measurement is not 1200 feet above thelevel of the sea. It is said that the water in the leather bottles,which Oudney’s caravan carried along with them, was frozen thissame night. But Major Denham, Clapperton’s companion,whom I desired, after his return from the lake Tchad, to give mesome oral explanation, told me, that, in the morning, some hours|334| after Dr Oudney’s death, the temperature of the air was not be-low 49° Fahr. (7\( \frac{1}{2} \)° R.). In South America, at a less distancefrom the equator, near Bogota and Quito, I saw the water freefrom ice, at the height of 8500 and 9000 feet, notwithstandingthe strong effect of the radiation of high plains in producing cold.In the manuscripts of young Beaufort, who died lately inUpper Senegal, a victim to scientific zeal, I find that underthe 16th degree of latitude, the thermometer marked in theshade on the same day 113° Fahr. (36° R.) at noon, and 59°Fahr. (12° R.) early in the morning. The temperature ofthe air in the plains of America never sinks so low in the samenorthern latitude. In laying before the Academy last year,a detailed account of the excellent labours of Ehrenberg andHemperich, I have already mentioned the cold to which theselearned travellers were exposed, when in the Desert of Dongolaunder the 19th degree of latitude. North winds penetrated intothis southern tropical country, and, in December, the thermo-meter sunk to 38° Fahr. (2° 5′ R.) above the freezing point, con-sequently 12° of R. lower than it had ever been observed, underthe same latitude, in the West Indies, according to the accountscarefully collected by myself. It is astonishing to find Africain its deserts colder than America, with all its rich vegetation,and this not on the margin of the tropics, but at the very centreof them. The true causes of this singular cooling processhave not yet been sufficiently explained. Perhaps it is the ra-diation of heat from the soil through the dry air towards a cloud-less sky, or a sudden expansion produced by the pouring ofhumid strata into this dry air, and the descent of the upperparts of the atmosphere. It is generally known that more than two-thirds of our planetare covered by a body of water, which, by its contact with the at-mosphere, exercises the most powerful influence upon the climateof the continents. The rays from the sun produce heat accordingto different laws, as they fall either upon the water or upon thesolid surface of the earth. The mobility of the particles ofwhich we imagine fluid bodies to be composed, produces cur-rents and an unequal distribution of temperature; cooled and con-densed by radiation, the particles of water sink to the bottom.By ascending in balloons, climbing upon insulated peaks of|335| mountains, by thermoscopic apparatus sunk into the sea, it hasbeen possible to determine the velocity of the cooling processwhich takes place at different seasons, from below upwards, in theatmosphere, and from above downwards, in the ocean, and infresh water lakes. The animals, therefore, which dwell in boththese elements, find on each point of the globe, in the aeriformand liquid elements, the most heterogeneous climates, placed instrata one above another. In the depth of the sea, under the Line,and in alpine lakes of the temperate zone, there is always a fixeddegree of cold, viz. that degree at which the water attains thegreatest density. The experiments of Ellis, Forster and Saus-sure, have been repeated under all zones and in all depths; butwhat we know of the lowest temperature of the air, and of sea-water, as well as of the greatest effect of the radiation of heat be-tween the tropics, serves as an infallible proof that the coldwhich there exists near the bottom of the sea, is produced by acurrent which, in the depths of the ocean, passes from the polestowards the equator, and cools the inferior strata of water in thesouthern ocean, like the current of air in the upper atmosphere,which moves from the equator to the poles, to temper the coldof the winter in the northern regions. The immortal Benjamin Franklin first taught us that sand-banks are sooner recognised by the thermometer than by thesounding line. They are islands of the submarine land, whichthe elastic subterranean powers had not been able to elevateabove the surface of the water. On the declivity of the shoals,the inferior and colder strata ascending by impulse, are mixedwith the upper and warmer ones; and thus the sudden cold ofthe sea-water shews to the navigator that danger is near. Theshallows, by their temperature, act on the air above them, inwhich they produce fogs and groups of clouds, which are per-ceived at a great distance. Before more extensive investigations had been made on thedistribution of heat over the globe, it was believed that the cli-mate of two places could be determined by the extremes of thetemperature in summer and winter. This view of things hasstill been preserved in popular opinion, whilst naturalists havelong ago renounced it as erroneous; for, although undoubtedlythe extremes of single days and nights are in a certain propor-|336| tion to the mean temperature of the year, yet the distribution ofheat in the different seasons is strikingly different, althoughthe mean annual temperature be one and the same,—a circum-stance which has a very great influence on the growth of plantsand on the health of man. I have endeavoured to determinethe law of this distribution, according to different situationsand heights. But comparative results in numbers ought to con-tain the mean temperature of every month, derived from thetwo extremes of every day, supposing an arithmetical series tobe formed. This method was first adopted by Reaumur in1735: he compared the produce of two harvests, not (like Her-schel) with the numbers and size of the spots in the sun, butwith the quantity of heat which the corn received in the time ofvegetation. Many labours have of late been directed towards as-certaining the hour, the mean temperature of which expressesalso that of the whole year. I here only mention the observa-tions carried on in Scotland at Leith Fort. The night watchof a military post has been employed for establishing observa-tions of the thermometer during two years, from hour to hour;and from the mass of these observations, which ought to be re-peated in other latitudes, it has been calculated, that, in the la-titude of Edinburgh, a single daily observation at 9 o’clock 13minutes in the morning, and in the evening at 8 o’clock 29 mi-nutes, would be sufficient to fix the average heat of the year *.Of the months, it is April and October which give this importantresult (a fact, first discovered by Leopold von Buch, whichis connected with remarkable modifications of the upper currentsof the atmosphere), except when, as in the island of Grand Ca-nary, local causes carry the maximum of heat to a later period,and place it in October. If I frequently allude to the great increase of meteorologicalobservations within the last twenty years, I by no means wishto express an opinion that the perfection of climatology is parti-cularly founded on such an increase. Here, as in all collec-tions of knowledge derived from experiments, which are toosoon denominated sciences, every thing depends on “an accu-

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* A result, which does not differ from the true by one-half degree ofReaumur’s thermometer, is also obtained by the mean of two hours ofthe same denomination.—Results of the Thermometrical Observations made atLeith Fort every hour of the day and night during the years 1824 and 1825, p. 19.|337| rate conception of nature,” and a just view of the conse-quences to be drawn from well-arranged facts. If we attempt toconceive the problem of the distribution of temperature in itsmost general sense, we may imagine the planetary heat either (asin the present oxydised, hardened surface of the earth) to be aconsequence of the position in relation to a central body, whichexcites heat; or (as in the first state of the condensation of matterdissolved in the form of vapour) the consequence of internalprocesses of oxidation, precipitation, change of capacity, or elec-tro-magnetic currents. Many geognostical phenomena, whichI have mentioned in another paper, seem to indicate such a de-velopement of internal heat, produced by our planet itself. More-over, the doubts raised against the peculiar heat in mines inboth parts of the world, have been entirely removed by recentexperiments of an ingenious astronomer M. Arago, on waterrising up through deep borings in what are called Artesian Wells.The greater the depth from which the water ascends, the warmerit has been found. In this case, there can be no suspicion ofstrata of air sinking down and being condensed, and consequent-ly disengaging heat; nor can the neighbourhood of men, or of thelanterns of miners, exercise an influence in this case. The waterscarry along with them the heat which they have acquired by along continued contact with rocky masses at different depths. These important observations shew how, independently of theobliquity of the ecliptic in the earliest, and, as it were, youthfulstate of our planet, the tropical temperature and tropical vege-tation could arise under every zone, and continue, till, by theradiation of heat from the hardened surface of the earth, and bythe gradual filling up of the veins with heterogeneous mineralsa state was formed, in which (as Fourier has shewn in a pro-found mathematical work) the heat of the surface, and of theatmosphere, depends merely upon the position of the planet to-wards a central body, the sun. We gladly resign to other na-tural philosophers the task to decide, how deep below the oxi-dised and hardened surface of the earth the melted fluid masseslie, which are poured out through the apertures of volcanoes,which periodically agitate the continents and the bottom of theocean, and force hot mineral springs upwards through clefts ingranite and porphyry. The depth of our mines is too inconsi-|338| derable to enable us, from the unequal increase of temperaturewhich has been hitherto observed in them, to give the satisfac-tory numerical solution of a problem which occupies the cu-riosity of men who live, as it were, upon a vault of rocks. Suf-fice it here to point out how the recent views of geologists haverevived the old mythus of Pyroplegeton and of Hephastos. When a planet is everywhere surrounded by aërial strata,and when the oxidised surface of the earth, with its cleftsalmost everywhere closed or filled up, by a long radiationof heat, has arrived at a state of equilibrium between receivingand losing, in such a manner that its external temperature andthe difference of climates arise solely from its position towardsthe sun, towards a larger central body which is perpetually ge-nerating light, then the problem of the temperature of any placein its most general form, may be considered as dependent solelyupon the manner in which the influence of the meridian heightof the sun manifests itself. This height determines, at the sametime, the magnitude of the semidiurnal circles, the density ofthe aërial strata, through which the rays of the sun pass, beforethey arrive at the horizon; it also determines the quantity of theabsorbed or calorific rays (a quantity which rapidly increaseswith the size of the angle of incidence); and, lastly, the numberof the rays of the sun, which, mathematically considered, a givenhorizon receives. The production of heat, as far as a greater orless is concerned, can accordingly be considered as proceedingfrom the illuminated surface of the earth. The absorptionwhich the rays of the sun undergo in their passage through theatmosphere, or (to express it in another manner) the productionof heat by the diminution of light is extremely small; but never-theless is perceptible on the ocean, where, at a great distancefrom the coast, and even when the water was colder than theatmosphere, I observed the temperature of the latter increasing atnoon with the height of the sun *. Recent researches † have shewn, that, in both continents,

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* Mr Arago has first called my attention to this remarkable effect of theabsorption of light in the atmosphere.—Con. des Tems pour 1828, p. 225.† Essai Politique sur l’Isle de Cuba, 1826, t. ii. p. 79-92. where I thinkI have obviated the doubts raised by Mr Atkinson.—Mem. of the Astron.Soc. vol. ii. p. 137, 137.|339| 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 ofGeminus on the Astronomical Poem of Aratus *, some Greekphilosophers believed the temperature of the tropics even to sur-pass that of the equator. M. Arago has, in a very ingeniousmanner, demonstrated, by numerous optical experiments, that,from the vertical incidence to a zenith distance of 20°, the quan-tity of the reflected light (and the lesser heating of the illumi-nated body depends on this quantity), remains almost thesame. In comparing the mean annual temperatures with oneanother, I find, that, in the western part of the old continent, thetemperatures diminish from the south towards the north in thefollowing proportion †:

From	20° to 30°	north Latitude.	3°.2	Reaum.
	30 40		3 .6
	40 50		5 .7
	50 60		4 .4

In both the continents, the region where the diminution of heatis most rapid, is to be found between 40° and 45° latitude. Inthis result, the observation agrees in a remarkable manner withthe theory; for the variation of the square of the cosines whichexpresses the law of the mean temperature, is largest at 45° lati-tude. This circumstance, as I have shown in another place, hasexercised a very beneficial influence on the state of civilisationof those nations who live in the mild countries, under this, themedium parallel of latitude. There the district where the vinegrows, borders upon that of the olive and orange tree. No-where else upon earth (in proceeding from the north to thesouth) does the heat increase more rapidly with the geographi-cal latitude; nowhere else do the various vegetable productions,used in gardening and in agriculture, succeed each other more

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* Esig. in Aratum eays. 13. Strabo, Geogr. lib. ii. p. 97.† In the eastern parts of the new continent, the diminutions of the meantemperature are as follows:

From	20° to 30°	Latitude,	5°	Reaum.
	30 40		5 .7
	40 50		7 .2
	50 60		5 .8

|340| rapidly. This variety animates industry and the commercialintercourse of nations. We may here state that partial, daily, and monthly changesof temperature are, on account of the motion of the atmosphere,produced by the transportation of colder or warmer strata, bygreater or less electric tension, by the formation of clouds or thediffusion of vapours; in short, by an almost infinite number of va-riable causes, acting at a greater or smaller distance. The studyof meteorology has, unfortunately, begun in a zone where thecauses are most complicated, and the number and intensity of thedisturbing powers greatest. If ever civilization, as may now beexpected, shall establish one of its principal seats in the tropics, itis to be presumed that these phenomena, which are so simplethere, will be more easily ascertained than in our climates, wherethe play of many conflicting causes has so long concealed themfrom our view. From that which is simple it is easy to proceed towhat is complicated, and we may imagine a scientific meteorolo-gy as returning from the tropics to the north. In the climateof palms, a feeble east wind always brings strata of air alongwith it, having generally the same temperature. The barometershows, like the progress of the needle, the hour of the day.Earthquakes, tempests, and thunder-storms do not disturb thesmall but periodical tides of the atmosphere. The changed decli-nation of the sun, together with the upper currents of the air,from the equator towards the pole, modified by this declina-tion, determine the beginning of the rainy season and the elec-tric explosions, which both begin at regular periods. The tra-veller may know his way almost as well by the direction of theclouds as by the compass; and, in the dry season, the appear-ance of a cloud on the deep blue sky would, in many districts ofthe tropics, astonish the natives as much as the fall of an aëro-lite or of the red polar snow would do us; or as the crash ofthunder in Peru; or, in the tropical plains, a hail storm. Thissimplicity and regularity in the meteorological phenomena allowus to expect an easier and more favourable insight into the re-lation of their causes. As long as the observations on the magnetic inclination, de-clination and intensity of forces, remained dispersed in the re-ports of travellers, and had not been united by magnetical lines,|341| the doctrine of the distribution of magnetism on the earth couldnot be expected to make any important progress. Supported byanalogy, it has been attempted to simplify by a careful employ-ment of well ascertained facts, the complicated doctrine of thedistribution of heat. Places having an equal mean temperatureof the year, of summer, or of winter, have been connected withone another by curves. This was the origin of the system ofisothermal lines *, of which I published a full account in theyear 1817. They descend towards the equator, because inEastern Asia and the eastern parts of North America we find,on an equal level above the sea, and in a more southern lati-tude, the same temperature which we meet with in the centreof Europe, in a more northern latitude. The remarkable cir-cumstance, that the highest civilization of the species to whichwe belong has developed itself, almost under the same latitudesin the temperate zone upon two opposite coasts, the easterncoast of the new and the western of the old continent, mustearly call our attention to the difference of heat under the samelatitudes. The question arose by how many thermometrical de-grees the old world was warmer than the new, and it is notlong since it was known, that the isothermal lines from the la-titude of Florida to that of Labrador, do not run parallel, andthat the eastern and western coasts of North America are al-most as different from one another as those of Western Eu-rope and of Eastern Asia. The shape and grouping ofthe continents, and their relation to the neighbouring seas,are the principal causes which determine the inflection of theisothermal lines, or the direction of equally warm zones, intowhich we may conceive the whole globe to be divided. Thepredominance of west winds in the temperate and cold re-gions determines the difference of climates on the eastern andwestern coasts of one and the same continent. The westernwinds, which are considered as reactions of the tropical trade-winds reach an eastern coast, after having traversed in wintera continent covered with snow and ice; to the western coasts,on the contrary (in Europe as well as in New California and

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* De la Distribution de la Chaleur sur le Globe.—Mem. de la Sociétéd’Arcueil, t. iii.|342| Nootka), western winds carry strata of air, which even inthe severest winter have been heated by contact with the vastsurface of the ocean. Led by these ideas, I have considered itof importance to obtain a knowledge of the lowest temperatureto which the Atlantic sinks, out of the Gulf Stream, between40° and 50° north latitude (consequently in the latitudesof Spain, France and Germany). I have found that, in themonth of January, in 40° latitude, the water of the sea does notsink below 56° Fahr. (10°.7 R.) and in 45° latitude not below54° Fahr. (9°.8 R.) The much esteemed geographer of India.Major Rennel, who for thirty years has been employed in study-ing the direction of the currents of the Atlantic, and who, duringmy last visit to England, communicated to me a part of his ma-nuscript materials, has, in 50° latitude, consequently in the zoneof the north of Germany, observed in winter a temperature ofthe sea-water, to which the atmosphere does not reach in themonth of January, even in the mild climate of Marseilles. Ifthe relative extent of Asia and North America, of the Pacificand the Northern Atlantic, was different from what it is, thewhole system of winds in the northern hemisphere, would, bythe unequal heating of the solid, as well as of the fluid, partsof the surface of the earth, be changed in their direction as wellas in their intensity. Europe is indebted for its milder climate to its position on theglobe (the position in which it stands in regard to the neighbour-ing seas) and to its peculiar form. Europe is the western partof the old continent; and consequently the great Atlantic Ocean,which already in itself has the power of diminishing the cold, andwhich is besides partly warmed by the Gulf Stream, lies to thewest of it. That part of the world which of all others enjoysthe greatest share of a tropical climate, the sandy Africa, is sosituate that Europe is heated by the strata of air, which, as-cending from Africa, move from the Equator towards the NorthPole. Had the Mediterranean not existed, the influence of Af-rica on the temperature and the geographical distribution ofplants and animals in Europe, would have been still more consi-derable. The third principal cause of the milder climate of Eu-rope is, that this part of the world does not approach the North|343| Pole nearly as much as America and Asia do; and that, on thecontrary, it lies opposite the greatest extent of sea-water, free fromice, which is known in the whole polar zone. The coldest pointsof the earth, which have lately been improperly called Poles ofCold, do not coincide with the magnetic poles, as Dr Brewster hasendeavoured to prove in the English version of my paper on theIsothermal Lines. According to Captain Sabine’s researches,the minimum of the annual mean temperature on the surface ofthe earth, is to the NW. of Melville’s Island, in the meridian ofBehring’s Straits, probably in 82° to 83° north Lat. The sum-mer boundary of the ice, which, between Spitzbergen and EastGreenland, recedes to 80° and 81° north Lat., is in about 75°N. Lat., every where between Nova Zembla, the Bone Islands ofNew Siberia and Icey Cape, the most western cape of America.Even the winter boundary of ice, the line on which the ice ap-proaches the nearest to our continent, scarcely surrounds BearIsland. From the North Cape, which is heated by a south-western current of the sea, the navigation to the most southernpromontory of Spitzbergen is never interrupted, not even in themost severe winters. The polar ice diminishes in quantitywherever it finds an opening to flow out, as in Baffin’s Bay, andbetween Iceland and Spitzbergen. The situation of the Atlan-tic Ocean exerts a most beneficial influence on the existence ofthat sea-water, free from ice, in the meridian of East Green-land and Spitzbergen, which has so important an influence uponthe climate of the north of Europe. On the other hand, the icebergs, which are driven from Baf-fin’s Bay and Barrow’s Straits to the south, accumulate in thatlarge mediterranean sea, which geographers designate by thename of Hudson’s Bay. This accumulation of ice increases thecold of the neighbouring continent so much, that, as reportedby Captain Franklin in his latest MS., in York Factory, andat the mouth of Hayes River, which lie in the same latitudesas the north of Prussia and Courland, in digging wells, ice isfound everywhere at the depth of four feet. The most northernand most southern boundaries of the fixed polar ice, that is, thesummer and winter boundaries, on the situation of which thetemperature of the northern continents depends, seem to havechanged but little, as far as historical records go; which fact|344| has been recently confirmed by careful inquiries. The in-jurious influence which small isolated masses of ice, drivensometimes by currents into the neighbourhood of the Azores,exercise, as it is said, upon the continent of Europe, is one ofthose tales, first derived from philosophers, and received by thevulgar, after the former have long ceased to believe in them. In the same latitudes, where, in the north of Europe, agri-culture and gardening are carried on, we find in NorthAmerica and North Asia only marshes and tracts of land co-vered with mosses: in the interior of Asia, on the other hand,the powerful radiation of heat, between the almost parallelchains of the Himalaya, the Zungling and the Himmelsgebirge,(a country on which Klaproth’s geographical researches havethrown great light), exercises the most beneficial influence onthe Asiatic population. The line of permanent snow, on thenorthern declivity of the Himalaya, lies 4000 feet higher thanon the southern; and the physical explanation which I havegiven of this singular phenomenon *, has, according to a reportof Mr Colebrooke, been confirmed by recent measurements andobservations in the East Indies. Millions of men of Thibetianorigin, of a gloomy religious cast of mind, occupy populoustowns, in a country where fields and towns would, during thewhole year, be buried in deep snow, if this high table-land wasless extensive and less continuous. As the currents of the atmosphere are modified in many dif-ferent manners, by changes in the declination of the sun, andby the direction of the chains of mountains on the declivities ofwhich they descend, the currents, also, of the liquid oceancarry the warmer waters of the lower degrees of latitude intothe temperate zone. I need not here mention how the watersof the Atlantic, always moved in the same direction by thetrade-winds, are carried against the dike formed by the isthmusof Nicaragua, then turn to the north, make the round of theGulf of Mexico, flow out through the Channel of the Bahamas,proceed as a current of warm water to the north-east towardsthe banks of Newfoundland, then to the south-east, towards thegroup of the Azores; and, when favoured by the north-west

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* Annales de Chimie et de Physique, tom. iii. p. 297; tom. ix. p. 310; tom.xiv. p. 5.|345| wind, carry along with them the fruits of palm trees from the An-tilles; casks of French wines from wrecked ships; nay, even livingEsquimaux in their leather boats from East Greenland, whichthey cast on the coasts of Ireland, of the Hebrides, or of Nor-way. A travelled astronomer, Captain Sabine, who, after re-turning from the Polar Regions, performed experiments withthe pendulum in the Gulf of Guinea, on the African Island ofSt Thomas, informed me, how casks of palm oil, which hadbeen lost by shipwreck at Cape Lopez, a little south of theEquator, were carried onwards, first by the equatorial current,and then by the Gulf Stream, crossing the Atlantic twice, fromeast to west, and from west to east, between 3° and 50° N. Lat.,safely arrived on the coasts of Scotland. The well preservedmark of the African proprietors left no doubt as to the direc-tion the casks had taken. In the same manner, as in this case,the equatorial waters in the Atlantic are carried north by theGulf Stream, I have, in the Pacific, in its southern hemisphere,observed a current (along the coasts of Chili and Peru), whichcarries colder water from higher latitudes to the Tropics. Inthis current I saw the thermometer, in the port of Truxillo, inthe month of September, fall to 61° Fahr. (12°.8 R.) and in theport of Callao, near Lima, at the end of November, to 60°Fahr. (12°.4 R.) A distinguished young officer of the Danishnavy, Baron Dirckinck von Holmfeldt, has, at my request, atdifferent seasons of the year 1825, observed this singular phe-nomenon, to which for so long a time no attention had beenpaid. Making use of thermometers, carefully compared by MrGay Lussac and myself, he again found the water of the sea, inthe port of Callao, in August 60\( \frac{1}{2} \)° Fahr. (12°.6 R.) and in March67\( \frac{1}{2} \)° Fahr. (15°.7 R.) Whilst, out of the current, at the pro-montory of Parina, the calm sea, as usually in those latitudes,showed the great heat of 79\( \frac{1}{2} \)° to 81°.5 (21° to 22° R.) Wecannot, in this place, explain how this stream of colder water,which increases the difficulty of the southern navigation fromGuayaquil to Peru, and from Peru to Chili, is for some monthsmodified in its temperature by the Garua, i. e. the vapours whichconstantly veil the sun; and how it renders the climate of theplains of Peru cooler. As all human attempts to arrive at a scientific view of the|346| phenomena of nature can have for their final object only a clearconception of our own nature, thus the investigation, with theprincipal topics of which we have now been occupied, at last leadsus to consider, how the differences of climate manifest themselvesin the character, in the civilization, and, perhaps, even in thedevelopment of the language of different tribes of the humanrace. This is the point where the important doctrine of the dis-tribution of heat over the globe comes to be connected with thehistory of mankind, and beyond which it ceases to be an ob-ject of purely physical inquiry.