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Alexander von Humboldt: „On Isothermal Lines, and the Distribution of Heat over the Globe“, in: ders., Sämtliche Schriften digital, herausgegeben von Oliver Lubrich und Thomas Nehrlich, Universität Bern 2021. URL: <https://humboldt.unibe.ch/text/1817-Des_lignes_isothermes-10> [abgerufen am 07.12.2024].
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| Titel | On Isothermal Lines, and the Distribution of Heat over the Globe | ||||||
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| Jahr | 1820 | ||||||
| Ort | Edinburgh | ||||||
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Nachweis in: The Edinburgh Philosophical Journal 3:5 (Juli 1820), S. [1]–20; 3:6 (Oktober 1820), S. 256–274; 4:7 (Januar 1821), S. 23–37; 4:8 (April 1821), S. 262–281; 5:9 (Juli 1821), S. 28–39.
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| Sprache | Englisch | ||||||
| Typografischer Befund | Antiqua; Auszeichnung: Kursivierung; Fußnoten mit Asterisken, Kreuzen, Paragraphen, Absatzmarken, Doppelstrichen; Schmuck: Initialen, Kapitälchen, Trennzeichen; Tabellensatz. | ||||||
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The distribution of heat over the Globe belongs to thatkind of phenomena, of which the general circumstances havebeen long known, but which were incapable of being rigorouslydetermined or submitted to exact calculation, till experienceand observation furnished data from which the theory mightobtain the corrections and the different elements which it re-quires. The object of this memoir is to facilitate the collectionof these data, to present results drawn from a great number ofunpublished observations, and to group them according to amethod which has not yet been tried, though its utility hasbeen recognised for more than a century in the exposition of thephenomena of the variation and dip of the magnetic needle.As the discussion of individual observations will be publishedin a separate work, I shall at present limit myself to a simplesketch of the distribution of heat over the globe, according tothe most recent and accurate data. Although we may not beable to refer the complex phenomena to a general theory, it
* As this interesting and valuable Memoir, the original of which was publishedin the Memoires D’Arcueil, tom. iii. p. 462, has never appeared in our language,and as it must be constantly referred to in all subsequent speculations on Meteoro-logy, and should be familiar to every person who pursues this important study, wehave resolved to present a translation of it to our readers. A small part of thememoir appeared in an English journal; but almost all the reductions from theCentigrade to Fahrenheit’s scale were so erroneous, that the numbers cannot betrusted. We have added various notes, which will be distinguished from those ofthe Author by affixing Ed. to the former, and H to the latter.—Ed. |2| will be of considerable importance to fix the numerical relationby which a great number of scattered observations are connect-ed, and to reduce to empirical laws the effects of local and dis-turbing causes. The study of these laws will point out to tra-vellers the problems to which they should direct their principalattention, and we may entertain the hope, that the theory of thedistribution of heat will gain in extent and precision, in propor-tion as observations shall be more multiplied, and directed tothose points which it is of most importance to illustrate. As the phenomena of geography and of vegetables, and ingeneral the distribution of organised beings, depend on theknowledge of the three co-ordinates of Latitude, Longitude, andAltitude, I have been occupied for many years in the exactvaluation of atmospherical temperatures; but I could not re-duce my own observations without a constant reference to theworks of Cotte and Kirwan, the only ones which contain a greatmass of meteorological observations obtained by instrumentsand methods of very unequal precision. Having inhabited fora long time the most elevated plains of the New Continent, Iavailed myself of the advantages which they present for exa-mining the temperature of the superincumbent strata of air,not from insulated data, the results of a few excursions tothe crater of a volcano, but from the collection of a greatnumber of observations made day after day and month aftermonth in inhabited districts. In Europe, and in all the OldWorld, the highest points of which the mean temperatureshave been determined, are the Convent of Peissenberg in Bavaria,and the Hospice of St Gothard *. The first of these is placedat 3264, and the second at 6808 feet above the level of the sea.In America a great number of good observations have beenmade at Santa Fe de Bogota and at Quito, at altitudes of8,727 and 9,544 feet. The town of Huancavelica, containing10,000 inhabitants, and possessing all the resources of moderncivilisation, is situated in the Cordilleras of the southern hemi-
* The mean temperature of the air at the Convent of the Great St Bernard, theheight of which is 7,960 feet, is not determined. There are several villages inEurope placed at more than 5000 feet of altitude; for example, St Jacques deAyas at 5,479, and Trinita Nuova, near Grasfoncy, at 5,315 feet.—H.|3| sphere at 12,310 feet of absolute elevation; and the mine ofSanta Barbara, encircled with fine edifices, and placed a leagueto the south of Huancavelica, is a place fit for making regularobservations, at the height of 14,509 feet, which is double thatof the Hospice of St Gothard. These examples are sufficient to prove how much our know-ledge of the higher regions of the atmosphere, and of the phy-sical condition of the world in general, will increase, when thecultivation of the sciences, so long confined to the temperatezone, shall extend beyond the tropics into those vast regions,where the Spanish Americans have already devoted themselveswith such zeal to the study of physics and astronomy. In or-der to compare with the mean heat of temperate climates, theresults which M. Bonpland and I obtained in the equinoctialregions from the plains to the height of 19,292 feet, it was ne-cessary to collect a great number of good observations made be-yond the parallels of 30° and 35°. I soon perceived how vaguesuch a comparison was, if I selected places under the meridianof the Cordilleras, or with a more eastern longitude, and I there-fore undertook to examine the results contained in the mostrecent works. I endeavoured to find, at every 10° of latitude,but under different meridians, a small number of places whosemean temperature had been precisely ascertained, and throughthese, as so many fixed points, passed my isothermal lines or linesof equal heat. I had recourse, in so far as the materials have beenmade public, to those observations the results of which have beenpublished, and I found, in the course of this easy, but longand monotonous labour, that there are many mean temperaturespointed out in meteorological tables, which, like astronomicalpositions, have been adopted without examination. Sometimesthe results were in direct contradiction to the most recent obser-vations, and sometimes it was impossible to discover fromwhence they were taken. Many good observations were rejected, solely because theabsolute height of the place where they were made was un-known. This is the case with Asia Minor, Armenia and Per-sia, and of almost all Asia; and while the equinoctial part aloneof the New World presents already more than 500 points, thegreater number of which are simple villages and hamlets, de- |4| termined by barometrical levelling, we are still ignorant of theheight of Erzeroum, Bagdad, Aleppo, Teheran, Ispahan,Delhi and Lassa, above the level of the neighbouring seas.Notwithstanding the intimate relation in which we have latelystood with Persia and Candahar, this branch of knowledge hasnot made any progress in the last fifty years. We are not authorised, however, on account of the decreaseof temperature in the upper regions of the atmosphere, to con-found the mean temperatures of places which are not placed onthe same level. In the Old World, good observations, which canalone be used for establishing empirical laws, are confined to anextent between the parallels of 30 and 70 degrees of latitude,and the meridians of 30° east longitude, and 20° of west longi-tude. The extreme points of this region are the island of Ma-deira, Cairo, and the North Cape. It is a zone which is only athousand nautical leagues, (1|7th of the circumference of theglobe,) from east to west, and which, containing the Basin of theMediterranean, is the centre of the primitive civilisation ofEurope. The extraordinary shape of this part of the world,the interior seas and other circumstances, so necessary for de-veloping the germ of cultivation among nations, have given toEurope a particular climate, very different from that of otherregions placed under the same latitude. But as the physicalsciences almost always bear the impress of the places where theybegan to be cultivated, we are accustomed to consider the distri-bution of heat observed in such a region, as the type of the lawswhich govern the whole globe. It is thus that, in geology, wehave for a long time attempted to refer all volcanic phenomenato those of the volcanoes in Italy. In place of estimating me-thodically the distribution of heat, such as it exists on the sur-face of continents and seas, it has been usual to consider asreal exceptions every thing which differs from the adopted type,or, by pursuing a method still more dangerous in investigatingthe laws of nature, to take the mean temperatures for every fivedegrees of latitude, confounding together places under differentmeridians. As this last method appears to exclude the influ-ence of extraneous causes, I shall first discuss it briefly before Iproceed to point out the method, essentially different, which Ihave followed in my researches. |5| The temperature of the atmosphere, and the magnetism ofthe globe, cannot, like those phenomena which depend on onecause, or on a single centre of action, be disengaged from theinfluence of disturbing circumstances, by taking the averages ofmany observations in which these extraneous effects are mutuallydestroyed. The distribution of heat, as well as the dip and va-riation of the needle, and the intensity of the terrestrial mag-netism, depend, by their nature, on local causes, on the consti-tution of the soil, and on the particular disposition of the radiat-ing surface of the globe. We must, however, guard againstconfounding under the name of extraneous and disturbing causes,those on which the most important phenomena, such as the dis-tribution and the more or less rapid developement of organiclife, essentially depend. Of what use would it be to have a tableof magnetic dips, which, in place of being measured in parallelsto the magnetic equator, should be the mean of observationsmade on the same degrees of terrestrial latitude, but under dif-ferent meridians? Our object is to ascertain the quantity ofheat which every point of the globe annually receives, and, whatis of most importance to agriculture, and the good of its inha-bitants, the distribution of this quantity of heat over the diffe-rent parts of the year, and not that which is due to the solaraction alone, to its altitude above the horizon, or to the dura-tion of its influence, as measured by the semidiurnal arcs. Moreover, we shall prove, that the method of means is unfitfor ascertaining what belongs exclusively to the sun, (inasmuchas its rays illuminate only one point of the globe,) and what isdue both to the sun and to the influence of foreign causes.Among these causes may be enumerated the mixture of the tem-peratures of different latitudes produced by winds;—the vicini-ty of seas, which are immense reservoirs of an almost invariabletemperature;—the shape, the chemical nature, the colour, theradiating power and evaporation of the soil;—the direction ofthe chains of mountains, which act either in favouring the playof descending currents, or in affording shelter against particularwinds;—the form of lands, their mass and their prolonga-tion towards the poles;—the quantity of snow which covers themin winter, their temperature and their reflection in summer;—and, finally, the fields of ice, which form, as it were, circumpolar |6| continents, variable in their extent, and whose detached partsdragged away by currents modify in a sensible manner the cli-mate of the temperate zone. In distinguishing, as has long been done, between the solar and the real climate, we must not forget, that the local and mul-tiplied causes which modify the action of the sun upon a singlepoint of the globe, are themselves but secondary causes, the ef-fects of the motion which the sun produces in the atmosphere,and which are propagated to great distances. If we considerseparately (and it will be useful to do this in a discussion pure-ly theoretical) the heat produced by the sun, the earth beingsupposed at rest and without an atmosphere, and the heat dueto other causes regarded as disturbing ones, we shall find thatthis latter part of the total effect is not entirely foreign to thesun. The influence of small causes will scarcely disappear bytaking the mean result of a great number of observations; forthis influence is not limited to a single region. By the mobilityof the aerial ocean, it is propagated from one continent to ano-ther. Every where in the regions near the polar circles, the ri-gours of the winters are diminished by the admixture of the co-lumns of warm air, which, rising above the torrid zone, arecarried towards the poles: Every where in the temperate zone,the frequent west winds modify the climate, by transportingthe temperature of one latitude to another *. When we re-flect, besides, on the extent of seas, on the form and prolonga-tion of continents, either in the two hemispheres, or to the eastand west of the meridians of Canton and of California, we shallperceive, that even if the number of observations on the meantemperature were infinite, the compensation would not take place. It is, then, from the theory alone that we must expect to deter-mine the distribution of heat over the globe, in so far as it dependson the immediate and instantaneous action of the sun. It doesnot indicate the degrees of temperature expressed by the dilata-tion of the mercury in a thermometer, but the ratios between themean annual heat at the equator, at the parallel of 45°, and un-der the polar circle; and it determines the ratios between thesolstitial and equinoctial heats in different zones. By comparing
* Raymond, Memoire sur la Formule Baromet. p. 108 and 113.|7| the results of calculation, not with the mean temperature drawnfrom observations made under different longitudes, but withthat of a single point of the earth’s surface, we shall set out withthat which is due to the immediate action of the sun, and to thewhole of the other influences, whether they are solar or local, orpropagated to great distances. This comparison of theory withexperience will present a great number of interesting relations. In the year 1693, previous to the use of comparable thermo-meters, and to precise ideas of the mean temperature of a place,Halley laid the first foundations of a theory of the heating ac-tion of the sun under different latitudes *. He proved that theseactions might compensate for the effect of the obliquity of therays. The ratios which he points out, do not express the meanheat of the seasons, but the heat of a summer day at the equa-tor and under the polar circle, which he finds to be as 1.834 to2.310 †. According to Geminus ‡, Polybius among the Greekshad perceived the cause why there should be less heat at theequator than under the tropic. The idea also of a temperatezone, habitable and highly elevated in the midst of the torridzone, was admitted by Eratosthenes, Polybius, and Strabo. In two memoirs §, published at long intervals in 1719 and1765, Mairan attempted to solve the problems of the solar action,by treating them in a much more extended and general manner.He compared, for the first time, the results of theory with thoseof observation; and as he found the difference between theheat of summer and winter much less than it ought to be bycalculation, he recognised the permanent heat of the globe andthe effects of radiation. Without mistrusting the observations he employed, he con-ceived the strange theory of central emanations which increasethe heat of the atmosphere from the equator to the pole. Hesupposes that these emanations decrease to the parallel of 74°,where the solar summers attain their maximum, and that theythen increase from 74° to the pole. Lambert ¶, with that
* Phil. Trans. 1693, p. 878.† This should be 2.339.—Ed. ‡ Isag. in Aratum, cap. 13.; Strabo, Geogr. lib. ii. p. 97.§ Mem. de l’Acad. 1719, p. 133; and 1765, p. 145. and 210.¶ Pyrometrie oder Vom Maase des Feuers, 1779, p. 342.|8| sagacity which distinguishes all his mathematical researches, haspointed out in his Pyrometrie the error of Mairan’s theory.He might have added, that this geometer confounds a quantityof heat which a point of the globe receives under the latitude of60° during the three months of summer, with the maximum towhich the inhabitants of these northern regions see theirthermometers rising in a clear day. The mean tempera-tures of the summers, far from decreasing from the pole to thetropics, are under the equator, under the parallel of 45°, andunder that of Stockholm, Upsal, or St Petersburg, in the ratioof 81°.86; 69°.8; 61°.16 of Fahrenheit’s scale. Reaumur hadsent his new thermometers to the torrid zone, to Syria, and to thenorth. As it was then reckoned sufficient to mark the warmestdays, an idea was formed of an universal summer, which is thesame in all parts of the globe. It had been remarked, and withreason, that the extreme heats are more frequent, and even morepowerful, in the temperate zone in high latitudes, than underthe torrid zone. Without attending to the mean temperatureof months, it was vaguely supposed, that in these northern re-gions the summers followed the ratio of the thermometrical ex-tremes. This prejudice is still propagated in our own day,though it is well established, that in spite of the length of thedays in the north, the mean temperatures of the warmest monthsat Petersburg, Paris, and the Equator, are 65°.66; 69°.44, and82°.4. At Cairo, according to the observations of Nouet, thethree months of summer are 84°.74, and consequently 19°warmer than at St Petersburg, and 15° warmer than at Paris.The summer heats of Cairo, are almost equal to those I haveexperienced at Cumana and La Guayra between the tropics. With regard to the central emanation of the system of Mai-ran, or to the quantity of heat which the earth gives to the am-bient air, it is easy to conceive that it cannot act in all seasons.The temperature of the globe at the depths to which we canreach, in general differs little from the mean annual temperatureof the atmosphere. Its action is of great importance for the pre-servation of vegetables; but it does not become sensible in theair, unless where the surface of the globe is not entirely coveredwith snow, and during those months, whose mean temperature |9| is below that of the whole year. In the south of France, forexample, the radiation of the earth may act upon the atmos-phere in the five months which precede the month of April. Wespeak here of the proper heat of the globe, of that which is in-variable at great depths, and not of the radiation of the surfaceof the globe, which takes place even at the summer solstice, andthe nocturnal effects of which have furnished M. Prevost withan approximate measure of the direct action of the sun *. Mairan had found, that in the temperate zone the heat of thesolar summer is to that of the solar winter as 16 to 1. M. Pre-vost admits for Geneva 7 to 1. Good observations have givenme for the mean temperature of the summers and the winters atGeneva 34°.7; 64°.94; and at St Petersburg 46°.94 and 62°.06.These numbers neither express ratios nor absolute quantities,but thermometrical differences considered as the total effect ofthe calorific influences; the ratios furnished by theory separatethe solar heat from every other indirect effect. Euler was notmore successful than Mairan in his theoretical essays on the so-lar heat. He supposes that the negative sines of the sun’s alti-tude during the night give the measure of the nocturnal cool-ing, and he obtains the extraordinary result †, that under theequator the cold at midnight ought to be more rigorous thanduring winter, under the poles. Fortunately, this great geo-meter attached but little importance to this result, and to the the-ory from which it is deduced. The second memoir of Mairan,without adding to the problems which had been attempted sincethe time of Halley, has at least the advantage of containing somegeneral views on the real distribution of heat in different conti-nents. It is true, that the extreme temperatures are there con-stantly confounded with the mean temperatures; but previousto the works of Cotte and Kirwan, it was the first attempt togroup the facts, and to compare the most distant climates. Dissatisfied with the route followed by his predecessors, Lam-bert, in his Treatise on Pyrometry, directed his attention to twovery different objects. He investigated analytical expressionsfor the curves, which express the variation of temperature in a
* Du Calorique rayonnant, p. 271. 277. 292.† Comment. Petrop. tom. ii. p. 98.|10| place where it had been observed, and he resumed in its great-est generality the theorem of solar action. He gives formulæ,from which we may find the heat of any day at all latitudes;but being perplexed with the determination of the nocturnal dis-persion of the acquired heat, or the subtangents of the noctur-nal cooling *, he gives tables of the distribution of heat underdifferent parallels, and in different seasons †, which deviate somuch from observation, that it would be very difficult to ascribethese deviations to the heat radiating from the globe, and to dis-turbing causes. We are struck with the slight difference whichthe theory indicates between the mean annual temperatures ofplaces situated under the equator and the polar circle, and be-tween the summers of the torrid zone and those of the tempe-rate zone. It cannot be expected, indeed, that analysis is ca-pable of determining the distribution of heat such as it existson the surface of the globe. Without employing empiricallaws, and deducing the data from actual observation, the theo-ry can subject to calculation only a part of the total effect,or that which belongs to the immediate action of the solar rays;but after the recent successful applications of analysis to thephenomena of the radiation of surfaces, the transmission of heatthrough solid bodies, and the cooling of these bodies in mediaof variable density, we may still expect to be able to perfectthe theory of solar action, and to compute the distribution ofthe heat received into the exterior crust of our planet. In discussing what may be expected from the purely theoreticallabours of Geometers, I have not spoken of a celebrated, butvery concise Memoir of Mayer, the reformer of the LunarTables. This work, written in 1755, was published twentyyears afterwards, in his Opera Inedita ‡. It is a method, and
* Pyrometrie, p. 141, 179.† Id. 318, 339.‡ De Variationibus Thermometri accuratius definiendis, (Opera inedita, vol. i.p. 3—10.) M. Daubuisson, in a note inserted in the Journal de Physique, tom. lxii.p. 449. has given a formula which accords better with observation than thatof Mayer. He admits that the temperature increases from the pole to the equa-tor, as the cosine of the latitude raised to the power of 2\( \left (\frac{1}{2} \right) \)°; but he judicious-ly adds, that this formula is applicable only to a zone of the Old World, nearthe Northern Atlantic Ocean—H.|11| not a theory: It is an essay essentially different from those wehave quoted, and, as its learned author calls it, a determinationof the mean heat found empirically by the application of co-efficients furnished by observation. The method of Mayer isanalogous to that which Astronomers pursue with so much suc-cess, when they correct by small steps the mean place of a planet,by means of the inequalities of its motion: It does not presentthe result of the solar action disengaged from the influence of fo-reign circumstances; but, on the contrary, it estimates the tem-peratures such as they are distributed over the globe, whateverbe the cause of that distribution. The mean heat of two placessituated under different latitudes being given, we find by a simpleequation the temperature of every other parallel *. The calcula-tions of Mayer, according to which the temperatures decrease fromthe equator to the poles, as the squares of the sines of the latitudes,give results sufficiently precise, when the place does not differmuch in longitude from that of the regions where the empiri-cal co-efficients have been obtained. But, even in the northernhemisphere, when we apply the formula to places situated 70°or 80° to the east or west of the meridian of Paris, the calcula-ted results no longer agree with observation. The curve whichpasses through those points whose temperature is 32°, does notcoincide with any terrestrial parallel. If, in the ScandinavianPeninsula, we meet with this curve under the 65th or 68th de-
* The formula given by Mayer was T = 24 cos 2 Lat.; or T = 12 + 12 cos2 Lat. for Reaumur’s scale; and T = 84—52 sin 2 Lat., or T = 58 + 26 cos 2 Lat.for Fahrenheit’s scale. Since the publication of Humboldt’s memoir, M. Daubuissonhas resumed the subject of the earth’s temperature in his Traité de Geognosie, tom. i.p. 424. Paris, 1819. He gives the following formula, which is almost the same as thatof Mayer, for finding the mean temperature, according to the Centigrade scale, viz.T = 27° cos 2 Latitude. This formula, which is superior in accuracy to Mayer’s, givesall the temperatures in defect for latitudes below 42°, and in excess for all the higherlatitudes, as appears from Daubuisson’s table. It is therefore obviously defective.M. Daubuisson, however, considers it as applicable principally between the paral-lels of 30° and 60° of N. lat. It ought to be remarked, that in the above formula,27° has been assumed as the mean temperature of the equator, in order to make theresults agree with observations made in the temperate regions, whereas the meantemperature of the equator, as ascertained by Humboldt, is 27°.5; and if this wereused in Daubuisson’s formula, it would make the differences still more in excess.— Ed. |12| gree of latitude, it descends, on the contrary, in North America,and Eastern Asia, to the parallel of from 53° to 58°. But thedirection and the inflexions of this curve of 32° of temperatureinfluences the neighbouring isothermal lines in the same man-ner as the inflexions of the magnetic equator modify the linesof inclination. To demand what is the mean temperature, orwhat is the magnetic inclination under a particular degree of la-titude, is to propose problems equally indeterminate. Though,even in high latitudes the magnetic and the isothermal lines arenot rigorously parallel to the magnetic equator, and to the curveof 32° of temperature; yet it is the distance of any place fromthis curve which determines the mean temperature, as the in-clination of the needle depends on the magnetic latitude. These considerations are sufficient to prove, that the empiri-cal formulæ of Mayer require the introduction of a co-efficient,which depends upon the longitude, and consequently on thedirection of the isothermal lines and their nodes with the ter-restrial parallels. Mayer had no intention of disengaging theresults which he obtained from the influence of all disturbingcauses: He limited himself to the determination of the effectsof altitude above the level of the sea, and those of the seasons,and the length of the day. He wished to point out the waywhich philosophers ought to pursue in imitating the method ofastronomers. His Memoir was written at a time when we didnot know the mean temperature of three points on the globe;and the corrections which I propose after tracing the isothermallines, so far from being incompatible with the method of Mayer,are, on the contrary, among the number of those which thisgeometer seems to have indistinctly foreseen. Kirwan, in his work on Climates, and in a learned Meteoro-logical Memoir, inserted in the eighth volume of the Memoirsof the Irish Academy, attempted at first to pursue the methodproposed by Mayer, but, richer in observations than his prede-cessors, he soon perceived, that after long calculations, theresults agreed ill with observation *. In order to try a newmethod, he selected, in the vast extent of sea, those places
* Kirwan’s Estimate of the Temperature of the Globe, chap. iii.|13| whose temperature suffered no change but from permanentcauses. These were in the part of the great ocean commonlycalled the Pacific Ocean, from 40° of South to 45° of North la-titude, and in the part of the Atlantic Ocean, between the pa-rallels of 45° and 80°, from the coasts of England to the GulfStream, the high temperature of which was first determined bySir Charles Blagden. Kirwan tried to determine for everymonth the mean temperature of these seas at different degrees oflatitude; and these results afforded him terms of comparisonwith the mean temperatures observed on the solid part of the ter-restrial globe. It is easy to conceive, that this method hasno other object, but to distinguish in climates that is in the to-tal effect of calorific influences, that which is due to the imme-diate action of the sun on a single point of the globe. Kirwanfirst considers the earth as uniformly covered with a thick stra-tum of water, and he then compares the temperatures of thiswater at different latitudes, with observations, at the surface ofcontinents indented with mountains, and unequally prolongedtowards the poles. This interesting investigation may enable us to appreciate theinfluence of local causes, and the effect which arises from theposition of seas, on account of the unequal capacity of water andearth for absorbing heat. It is even better fitted for this ob-ject than the Method of Means deduced from a great numberof observations made under different meridians; but in the ac-tual state of our physical knowledge, the method proposed byKirwan cannot be followed. A small number of observationsmade far from the coasts, in the course of a month, fixes, with-out doubt, the mean annual temperature of the sea at its surface,and, on account of the slowness with which a great mass of wa-ter follows the changes of the temperature of the surroundingair, the extent of variations in the course of a month is smallerin the ocean than in the atmosphere: But it is still greatly to bedesired *, that we should be able to indicate by direct experi-ence, for every parallel, and for every month, the mean tempe-rature of the ocean under the temperate zone. The schemewhich Kirwan has formed for the extent of the seas, that ought to
* See my Relation Historique, tom. i.|14| form the term of comparison, is founded only in a small degreeupon the observations of navigators, and to a great degree onthe theory of Mayer. He has also confounded experimentsmade on the superficial temperature of the ocean with the re-sults of meteorological journals, or the indications of the tem-perature of the air which rests upon the sea: He has obvious-ly reasoned in a circle, when he modified, either by theoreticalsuppositions or by observations made on the air upon the coasts ofcontinents, the table of the temperature of the ocean, in orderto compare afterwards with these same results, partly hypothe-tical, those which observation alone furnished in the interior ofthe earth. After the works of Kirwan, we must notice thoseof Cotte, which are merely laborious, though useful, compila-tions, which, however, ought not to be used without much cir-cumspection. A critical spirit has rarely presided over the re-duction of the observations, and they are not arranged so as tolead to general results. In detailing the actual state of our knowledge on the distri-bution of heat, I have shewn how dangerous it is to confoundthe results of observation with theoretical deductions. Theheat of any point of the globe depends on the obliquity of thesun’s rays, and the continuance of their action, on the height ofthe place, on the internal heat and radiation of the earth in themiddle of a medium of variable temperature; and, in short, up-on all those causes which are themselves the effects of the rota-tion of the earth, and the inequal arrangement of continentsand seas. Before laying the foundation of a system, we mustgroup the facts, fix the numerical ratios, and, as I have alreadypointed out, submit the phenomena of heat, as Halley did thoseof terrestrial magnetism, to empirical laws. In following thismethod, I have first considered whether the method employedby meteorologists for deducing the mean temperature of theyear, the month and the day, is subject to sensible errors.Assured of the accuracy of the numerical averages, I havetraced upon a map the isothermal lines, analogous to themagnetic lines of dip and variation. I have considered themat the surface of the earth in a horizontal plane, and on thedeclivity of mountains in a vertical plane. I have examined |15| the increase of temperature from the pole to the equator, whichis inequal under different meridians; the distribution of the samequantity of heat over the different seasons, in the same isother-mal parallel, and under different latitudes; the curve of perpe-tual snows, which is not a line of equal heat; the temperatureof the interior of the earth, which is a little greater towards thenorth, and in high mountains, than the mean temperature ofthe atmosphere under the same parallel; and, lastly, the distri-bution of heat in the ocean, and the position of those bands,which may be called Bands of the warmest waters. As thelimits of this extract will not permit me to enter, in a detailedmanner, upon these different discussions, I shall confine myselfsolely to the principal results. It was formerly the custom to take the maximum and mini-mum of temperature observed in the course of a year, and toconsider half the sum as the mean temperature of the wholeyear. This was done by Maraldi, De la Hire, Muschenbröek,Celsius, and even Mairan, when they wished to compare thevery warm year of 1718 with the excessively cold years of 1709and 1740. De la Hire was struck with the identity betweenthe uniform temperature of the caves of the Observatory of Pa-ris, and the mean of the observed annual extremes. He ap-pears to have been the first who had an idea of the mean quan-tity of heat which a point of the globe receives; and he adds,“We may regard the air of the caves as the mean state of theclimate *.” Reaumur followed also the method of a maximum, though he confessed that it was incorrect †. He noticed thehours at which it was necessary to make observations; and after1735, he published in the Memoirs of the Academy the ex-tremes of daily temperature: he even compared the produce oftwo harvests with the sum of the degrees of heat to which duringtwo consecutive years the crops had been exposed. When hetreated, however, of the mean temperature of the month, hecontented himself, as Duhamel did thirty years afterwards,with recording three or four thermometrical extremes. In orderto have some idea of the errors of this imperfect method, I may
* Mem. de l’Acad. 1719, p. 4.† Id. 1735, p. 559.|16| state, that even in 1777, the mean temperature of Toulon wasestimated by Cotte * at 78°.08, though he afterwards found, byemploying the whole mass of observations, that it was not morethan 60°.26. In order to diminish the errors of the method of annual ex-tremes, it was perceived, though very late, that it was necessaryto subdivide the curve which expresses the variation of tempe-rature. Twenty-four extremes divided among twelve monthsof the year, give an annual mean more exact than the two ex-tremes of all the observations. The ordinates do not increaseuniformly and uninterruptedly up to the maximum of the year,and there are partial inflexions sufficiently regular. The morewe subdivide, and the more we know the terms in the series,the more will these terms approximate, and the less error willthere be in the supposition of an arithmetical progression, andin that of the equidistance of the different maxima and minima of temperature. These considerations enable us to appreciatethe three methods according to which observations are at presentmade. 1. Observations are made three times a-day, at sunriseand sunset, and at two o’clock in the afternoon. This was doneat Geneva during the three years 1796, 1797 and 1798. In theobservations, the hour of mid-day was preferred to that of sunset.2. Observations are made twice every day, at the two periodswhich are supposed to give the maximum and the minimum,namely, at sunrise, and at two o’clock in the afternoon. 3. Ob-servations are made once a-day, at an hour which, in differentseasons, has been found to represent the mean temperature ofthe day. It is thus that M. Raymond, by a judicious induc-tion, has proved, that the height of the barometer, at mid-day,gives, in our climates, the mean atmospherical pressure, correct-ed for the diurnal variation. In calculating † a great number of observations made be-tween the parallels of 46° and 48°, I have found, that a singleobservation at sunset, gives a mean temperature which differsonly some tenths of a degree from that which is deduced fromobservations made at sunrise and at two o’clock. The devia-
* Mem. de la Soc. Royale de Med. 1777, p. 104.† De la Formule Barom. p. 213.|17| tions of different months, do not exceed 1°.8, and they are veryregularly positive or negative, according to the order of the sea-sons. M. Arago * has examined for seven years the observationsof noon. They give for Paris 5°.4 more than the mean tempera-ture of the whole year. Upon high mountains in the tempe-rate zone, the difference is scarcely 1°.8 †. By the applicationof coefficients, variable according to the latitude and the eleva-tion, we may deduce the true mean temperatures from observa-tions made at any particular period of the day, nearly in thesame manner as we can ascertain the latitude of a place fromaltitudes of the sun, taken out of the meridian. If we do not stop at two observations of the maximum andminimum, but add a third observation, we commit an error moreor less serious, if we divide simply by three the sum of the ob-servations, without attending to the duration of the partial tem-peratures, and to the place which the third observation occupiesbetween the last terms of the series ‡. Experience proves, thatthe mean temperatures of the year, obtained by two or three ob-servations, do not differ sensibly, if the intermediate observationis sufficiently distant (four or five hours) from the observationof the maximum and minimum. Whenever, therefore, we donot take into account the duration of the intermediate tem-peratures, we should prefer the two observations of the ex-treme temperature, which is the method most generally adopted.We shall content ourselves with pointing out the errors to which
* The mean of the observations at noon at Paris was 56°.84; at Clermontin Auvergne (elevation 1348 feet), 56°,30; at Strasburg (elevation 453 feet),55°.22. Bulletin de la Soc. Philom. 1814, Oct. p. 95.—H.† At the Hospice of St Gothard. Ephem. Soc. Pal. 1785, p. 47.‡ Example.—On the 13th June, at 4h in the morning, 46°.4; at 2h in the af-ternoon, 55°.4; and at 11h in the evening, 50°, (erroneously 46°.4, or 8° Centig.in the original). In calculating by the duration, we have
The true mean of which is 51°.0. The mean of the three observations, as com-monly taken, is 50°.6. If we stop at the two extreme temperatures, we shall havefor their half sum 50°.45.—H.|18| it is liable. In our climates, the two extreme terms do not di-vide the series of twenty-fours into two equal parts. The maxi-mum is an epoch nearly fixed: the rising of the sun retards orhastens it three hours. As we ought to take into account theduration of the partial temperature, in order to find the quan-tity of heat divided between the night and the day, we mustcouple the maximum of one day with the minimum of theday following, and not be content with taking half the sum ofall the maxima and minima of a month. In the ordinary me-thod, we determine only the mean temperature of the part ofthe day comprehended between the rising of the sun and twoo’clock in the afternoon; and we take it for granted that themean temperature is the same * from two o’clock to sunrise nextday. This double error, of want of equi-distance and of thecoupling of observations, does not in general produce errors ofmore than some tenths of degrees, sometimes in excess, and some-times in defect, since the warm and cold days are mixed †.
All the calculated results will err in defect, if the 365 ordi-nates, through which the curve of the year passes, do notexpress an arithmetical progression, and if the partial irre-gularities do not sensibly compensate one another. It is onlyon this supposition that we can judge by the extreme terms ofthe series, of the sum of the terms, that is, of the partial tempe-ratures. It is very obvious, that near the maximum, the in-crease ought to be more slow than in other points of the curve,and that this increase in the temperature of the air ought todepend on the sine of the sun’s altitude, and on the emission ofthe radiant heat of the globe.
* Example.—At sunrise at 6h, 50°; at 2 o’clock in the afternoon, 62°.6. Atsunset, 51°.8; at 2h, 66°.2; at sunrise, 50°. The true means will be for the first24 hours 56°.9, and for the second 59°.0, for we shall have
* On the 3d and 4th September 1811, lat. 48°.50′.
The three last days shew an equality of temperature, which is very surprising,and which does not appear but in the true means.—H.|20| ing curve. In the morning the true mean temperature, such aswe find by taking the duration into account, is a little greaterthan half the sum of the extremes *. In the evening the erroris in a contrary direction, and the series of temperatures ap-proaches more to a progression by quotients. The differencesdo not in general exceed half a degree, and calculation provesthat the compensation is regular. It would be curious to exa-mine the effect which the radiation of the earth has on these ho-rary effects, as the changes of temperature at the surface donot follow the geometrical progression, in so far as they takeplace in a medium of uniform temperature.
In order to avoid the use of an arbitrary measure, astrono-mers express the diameters of the planets by taking that of theearth for unity. In like manner, I express the mean tempera-tures not in parts of the equatorial heat, but by the arithmeticalratios which subsist between this heat and that of the other paral-lels. This method frees us from the want of uniformity, whicharises from the use of different thermometers. Instead of say-ing that in Europe, under the parallel of 45°, the mean tempe-rature is 13°.4 Centigrade, or 56°.12 of Fahrenheit, we say thatit is = 1.0°,487, and in lat. 55° = 1.0°,29. These arithmeticalratios inform us of what is most interesting in the theory of thedistribution of heat, that in thermometers whose zero is thepoint of melting ice, the mean temperatures under the latitudeof 45° and 55° are, in our regions, the half and the third near-ly of the equatorial temperature, which I suppose to be 81°.5.
(To be continued.)
* Example.—Latitude 10°.25′.
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Having discussed the method of taking averages, and ofreducing temperatures to general expressions, we shall now pro-ceed to trace the course of the Isothermal Lines on the surfaceof the Globe, and at the level of the sea. From a slight at-tention to the difference of climates, it has been remarked, morethan a century ago, that the temperatures are not the same un-der the same parallels; and that in advancing 70° to the east orthe west, the heat of the atmosphere suffers a sensible diminution.In pursuance of our method, we shall reduce these phenome-na to numerical results, and shew that places situated underthe same latitudes do not differ, in America and Europe, bythe same number of degrees of temperature, as has been vague-ly stated. This assertion would make us suppose that the iso-thermal lines are parallel in the temperate zone.
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This table † indicates the difference of climates, expressed bythat of the mean temperature, and by the number of degreesin latitude which it is necessary to go northward in Europe, in
* The differences under the column of latitudes, is the difference of the latitudeof a place in Europe and a place in America, which have the same mean tempera-ture; and the differences under the column of mean temperatures, is the differenceof the mean temperatures of a place in Europe and a place in America, whichhave the same latitude.—Ed. † See my Prolegomena de distributione geographica plantarum, secundum cœlitemperiem et altitudinem montium. p. 68.—H.|258| order to find the same quantity of annual heat as in America. As a place could not be found in the Old World, whose meantemperature was 48° the same as that of Williamsburg, I havesupplied it with an interpolation between the latitudes of twopoints whose mean temperatures are 56°.5 and 59°.4. By ananalogous method, and by employing only good observations, Ihave found that 1. The isothermal line of 32° (0° centig.) passes between Uleo and Enontekiesin Lapland (lat. 66° to 68°; East long. from London 19° to 22°), and Table Bay inLabrador (lat. 54° 0′, west long. 58°.) 2. The isothermal line of 41° (5° centig.) passes by near Stockholm (lat. 60°east long. 18°) and the Bay of St George in Newfoundland (lat. 48°, and long. 59°.) 3. The isothermal line of 50° (10° centig.) passes by Belgium (lat. 51°, east long.2°) and near Boston (lat. 42° 30′, west long. 70° 59.) 4. The isothermal line of 59° (15° centig.) passes between Rome and Florence(lat. 43° 0′, east long. 11° 40′) and near Raleigh in North Carolina (lat. 36° 0′, andwest long. 76° 30′.) The direction of these lines of equal heat, gives for the twosystems of temperature, which we know by precise observations,viz. part of the middle and west of Europe, and that of thecoast of America, the following differences:
If we call the mean equatorial temperature 1, we shall havethe half of this temperature in the Old World at 45°, and inthe east of the New World, at 39° of lat *.
The mean temperatures decrease
In both continents, the zone in which the mean temperaturedecreases most rapidly is comprehended between the parallels of
* This observation relates to the Centigrade scale. If we count the tempera-tures from 32°, it applies also to Fahrenheit’s scale.—Ed. |259| 40° and 45°. Observation here presents a result entirely con-formable to theory, for the variation of the square of the cosine,which expresses the law of the temperature, is a maximum to-wards 45° of latitude. This circumstance ought to have a favour-able influence on the civilization and industry of the peoplewho inhabit the regions under this mean parallel. It is thepoint where the regions of the vines touch those of the olivesand the citrons. On no other part of the globe, in advancingfrom north to south, do we observe the temperatures increasemore sensibly, and no where else do vegetable productions, andthe various objects of agriculture, succeed one another withmore rapidity. But a great difference in the productions ofcontiguous countries, gives activity to commerce, and augmentsthe industry of the cultivators of the soil. We have traced the direction of the isothermal lines fromEurope to the Atlantic Provinces of the New World. Wehave seen them approach one another from parallelism towardsthe south, and converge towards the north, particularly be-tween the thermometric curves of 41° and 50°: We shall nowendeavour to pursue them to the west. North America pre-sents two chains of mountains, extending from N. E. to S. W.,and from N. W. to S. E. forming almost equal angles with themeridian, and nearly parallel to the coasts which are oppositeto Europe and Asia, viz. the chain of the Alleghanys and the Rocky Mountains, which divide the waters of the Missouriand the Columbia. Between these chains stretch the vast ba-sin of the Mississippi, the plains of Lousiana, and of the Tenes-see, and the states of Ohio, the centre of a new civilization. Itis generally believed in America that the climate is more mildto the west of the Alleghany Mountains, than under the sameparallels in the Atlantic States *. Mr Jefferson, has estimatedthe difference at 3° of latitude; and the Gleditsia monosperma, the Catalpa, and the Aristolochia Sypho, and other vegetableproductions, are found so many degrees farther to the north, inthe basin of the Ohio, than on the coast of the Atlantic †.
* This is true also of the Columbian Valley. See Warden’s Account of theUnited States, vol. iii. p. 169.—Ed. † See my Essai sur la Geographie des Plantes, p. 154.|260| M. Volney has endevoured to explain these phenomena by thefrequency of the south-west winds, which drive back the warmair of the Gulf of Mexico towards these regions. A series ofgood observations, made for seven years by Colonel Mansfieldat Cincinnati, on the banks of the Ohio, and recently publish-ed by Mr Drake, in an excellent treatise on American meteoro-logy *, has removed the doubts which obscured this point. Thethermometrical means prove that the isothermal lines do notrise again in the regions of the west. The quantity of heatwhich each point of the globe receives under the same parallels,is nearly equal on the east and the west of the Alleghany range,the winters being only a little milder to the west, and the sum-mers a little warmer †. The migrations of vegetables towardsthe north are favoured in the basin of the Mississippi, by theform and the direction of the valley which opens from thenorth to the south. In the Atlantic Provinces, on the contra-ry, the valleys are transverse, and oppose great obstacles to thepassage of plants from one valley to another. If the isothermal lines remain parallel, or nearly so, to theequator, from the Atlantic shores of the New World to the eastof the Mississippi and the Missouri, it cannot be doubted thatthey rise again beyond the Rocky Mountains, on the oppositecoast of Asia, between 35° and 55° of latitude. To the consi-
* Natural and Statistical View or Picture of Cincinnati and the Miami Coun-try, 1 vol. 8vo. Cincinnati.—H. See Warden’s Account of the United States, vol. ii. 236 for an abstract of Mr Drake’s results.—Ed. † The following comparison of the mean temperatures has been deduced withgreat care. |Spaltenumbruch|
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I have taken for Philadelphia the means between the observations of Coxe andRush. I have also referred for correction to the observations made by M. Legauxat Spring-Mill upon the Schuylkill, to the north of Philadelphia. As Cincinnatiis 512 feet above the level of the sea, its mean temperature is 1°.4 too low.– H.|261| derations which I pointed out in my work on Mexico *, are tobe added the observations of Captain Lewis, and some otherAnglo-American travellers, who have passed the winter on thebanks of the Columbia. In New California, they cultivatewith success the olive, along the canal of Santa Barbara, andthe vine from Monterey to the north of the parallel of 37°,which is that of Chesapeake Bay. At Nootka, in the Islandof Quadra and Vancouver, and almost in the latitude of La-brador, the smallest rivers do not freeze before the month ofJanuary. Captain Lewis saw the first frosts near the embou-chure of the Colombia, only on the 7th of January, and therest of the winter was rainy. Through 122° 40′ of west long.the isothermal line of 50° Fahr. appears to pass almost as inthe Atlantic part of the Old World, at 50° of lat. The west-ern coasts of the two worlds resemble one another to a certainpoint †. But these returns of the isothermal lines do not extendbeyond 60°. The curve of 32° Fahr. is already found to thesouth of the Slave Lake, and it comes still farther south inapproaching Lakes Superior and Ontario.
In advancing from Europe towards the east, the isothermallines again descend ‡, the number of fixed points being few.We can only employ those which are made in places whoseknown elevation allows us to reduce the mean temperatures tothe level of the sea. The few good materials which we possess,have enabled us to trace the curves of 32° and 55°.4. We knoweven the nodes of the latter curve round the whole globe. It
* Essai Politique sur la Nouvelle Espagne, tom. ii. p. 440, 478, 509.† On account of the influence of west and south-west winds. See Dalton’s Meteor. Observ. p. 125.‡ In comparing places from the west to the east, and nearly under the sameparallel, we find, |Spaltenumbruch|
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The elevation of Pekin is inconsiderable. That of Moscow is 984 feet. Theabsolute temperature of Madrid, to the west of Naples, is 59°; but the city iselevated 1978 feet above the level of the sea.—H.|262| passes to the N. of Bourdeaux, (lat. 45° 46′, W. long. 0° 37′,)near Pekin, (lat. 39° 54′, E. long. 116° 27′.,) and Cape Foul-weather to the S. of the embouchure of the Colombia, (lat.44° 40′, W. long. 104°.) Its nodes are distant at least 162°of longitude. We have here pointed out only the empiri-cal laws, under which are ranged the general phenomena,and the variations of the temperature which embrace at once avast extent of the globe. There are partial inflexions of theisothermal lines, which form, so to speak, particular systemsmodified by small local causes; such as the strange inflexion ofthe thermometric curves on the shores of the Mediterranean,between Marseilles, Genoa, Lucca and Rome *, and thosewhich determine the difference between the climate of the wes-tern coast and the interior of France. These last depend muchless on the quantity of heat received by a part of the globeduring the whole year, than upon the unequal distribution ofheat between winter and summer. It will one day be usefulto have upon particular charts the partial inflections of the iso-thermal lines, which are analogous to the lines of soundings orof equal declivity. The employment of graphical representa-tions will throw much light upon phenomena, which are deeplyinteresting to agriculturists. If, in place of geographical charts,we possessed only tables containing the co-ordinates of latitude,longitude, and altitude, a great number of curious facts rela-tive to the configuration and the superficial inequalities of con-tinents would have remained forever unknown.
We have already found, that towards the north, the isother-mal lines are neither parallel to the equator nor to one another;and it is on account of the want of parallelism, that we have,in order to simplify such complicated phenomena, traced roundthe whole globe the curves of equal heat. The position of theline of 32° acts like the magnetic equator, whose inflexions inthe South Sea modify the inclinations at great distances. Wemay even believe that, in the distribution of climates, the lineof 32° determines the position of the curve of greatest heat,
* |Spaltenumbruch|
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|263| which is as it were the isothermal equator, and that in Americaand Asia through 78° of west, and 102° of east longitude, thetorrid zone commences more to the south of the tropic of Can-cer, or that it there presents temperatures of less intensity. Anattentive examination of the phenomena proves that this is notthe case. Whenever we approach the torrid zone below theparallel of 30°, the isothermal lines become more and moreparallel to one another, and to the earth’s equator. The greatcolds of Canada and Siberia do not extend their action to theequatorial plains. If we have long regarded the Old World aswarmer between the tropics than the new world, it is, first, Be-cause till 1760, travellers used thermometers of spirit of wine,coloured, and affected by light; 2d, Because they observed iteither under the reflection of a wall, or too near the ground,and when the atmosphere was filled with sand; and, 3d, Be-cause in place of calculating the true mean, they used onlythe thermometric maximum and minimum. Good observa-tions give,
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The mean temperature of the equator cannot be fixed be-yond 81\( \frac{1}{2} \)°. Kirwan values it at 84°, but only two places of theearth were known, viz. Chandernagor and Pondicherry, towhich old travellers attributed annual temperatures above 81°\( \frac{1}{2} \).At Chandernagor, in latitude 21°.6, the mean temperature, ac-cording to Cotte, is 91°.9, but the Jesuite Boudier marked onlythe days when the thermometer was above 98°.6, and below57°.2. And at Pondicherry, in latitude 11° 55′, the mean tem-perature, according to Cotte, is 85°.3, and according to Kirwan,88°; but M. de Cossigny observed with a spirit-of-wine thermo-meter.
The distribution of heat over different parts of the year differs,not only according to the decrease of the mean annual tempera-tures, but also in the same isothermal line. It is this unequaldivision of the heat which characterises the two systems ofclimate of Europe and Atlantic America. Under the torridzone, a small number of months are warmer in the Old Worldthan in the New. At Madras, for example, according to Dr
|264| Roxburgh, the mean temperature of June is 89°.4; at Abu-sheer 93°.2, but at Cumana I have found it only 84°.6.
With respect to the temperate zone, it has been long known,that from the parallel of the Canary Isles to the Polar Circle,the severity of the winter augments in a progression much morerapid than the summers diminish in heat. It is also known,that the climate of the islands and the coasts differs from that ofthe interior of continents, the former being characterised bymild winters and less temperate summers. But it is the heatof summer particularly which affects the formation of the amy-laceous and saccharine matter in fruits, and the choice of the plantsthat ought to be cultivated. As the principal object of this me-moir is to fix, after good observations, the numerical relationsbetween the unequal quantities of heat distributed over theglobe, we shall now compare the mean temperatures of threemonths of winter and summer under different latitudes, andshew how the inflections of the isothermal lines modify theserelations. In following the curves of equal heat from west tocast, from the Basin of the Mississippi to the eastern coasts ofAsia, through an extent of 4000 leagues, we are struck withthe great regularity which appears in the variations of the win-ter temperature.
I. Differences of the Seasons from the Equator to the PolarCircle.
This table shews the increase of the difference between thewinters and summers from 28° and 30° to the parallels of 55°and 65°. The increase is more rapid in the TransatlanticZone, where the isothermal lines of 32° and 50° approach oneanother very much; but it is remarkable, that in the two zoneswhich form the two systems of different climates, the division of
|265| the annual temperature between winter and summer is made insuch a manner, that, upon the isothermal line of 32°, the diffe-rence of the two seasons is almost double of that which isobserved on the isothermal line of 68°.
If, instead of the mean temperatures of the seasons, we con-sider, I do not say the days of the maxima and minima of theyear, which are the ordinates of the concave and convex sum-mits of the entire curve, but the mean temperatures of thewarmest and the coldest month, the increase of the differencesbecomes still more perceptible. We request the reader to com-pare in the following Table only the places which belong toregions bounded by the same meridians, and consequently to thesame system of climate; as for example, to the region of Eas-tern America to that of Western Europe, and that of EasternAsia. We must also attend to the changes of temperature pro-duced by the monsoons in a part of the equinoctial regions, and
|266| distinguish under the temperate zone between the climate of theinterior, or the continental climate, and that of islands and coasts.
We may conclude in general, that for any given place in thecurves which express the annual temperatures, the ordinates ofthe concave and convex summits differ the more from one ano-ther, as the temperatures diminish. In the New World, under40° of latitude, we find a greater difference between the warm-est and coldest months of the year than in the Old World, atCopenhagen and Stockholm under 56°—59° of latitude. AtPhiladelphia the thermometer descends to 50° or 59° belowthe freezing point, while under the same parallel in Europeit descends scarcely 30°.6 below it.
I have endeavoured to shew, in another work, how this cir-cumstance which characterises the regions which Buffon indi-cates by the name of Excessive Climates, influences the physi-cal constitution of the inhabitants. In the United States, theEuropeans, and indeed all the natives, are, with great difficulty,inured to the climate. After winters that have been very rigo-rous, not from the general temperature, but from an extreme de-pression of the thermometer, the irritability of the nervous sys-
|267| tem is prodigiously increased by the excessive heat of summer;and it is undoubtedly to this cause that we must, in a greatmeasure, ascribe the difference in the propagation of the yellowfever, and the different forms of the marsh fever, under theequator, and in the temperate zone of the New World *. Onhigh mountains in islands of little extent, and along the shores,the lines of annual temperature take nearly the same form as inwarm climates, having only a less degree of curvature. Thedifference between the seasons, too, becomes smaller. At theNorth Cape, in 71° of latitude, and in the isothermal line of32°, it is almost 11° greater than at Paris, in 49° of latitude,and in the isothermal line of 50°. The sea-breezes and thefogs which render the winters so temperate, diminish at thesame time the heats of summer †. The characteristic of anyclimate is not the difference between the winters, expressed indegrees of the thermometer;—it is this difference, comparedwith the absolute quantities indicated by the mean temperatureof the seasons.
II. Difference between the Winters and Summers, in followingthe same Isothermal Line from West to East.
The differences between the seasons of the year are less greatnear the convex summits of the isothermal curves, where thesecurves rise again towards the North Pole, than near the concavesummits. The same causes, which affect the inflexion or thegreatest curvature of the isothermal lines, tend also to equalisethe temperatures of the seasons.
The whole of Europe, compared with the eastern parts ofAmerica and Asia, has an insular climate, and, upon the sameisothermal line, the summers become warmer, and the winterscolder, in proportion as we advance from the meridian of MontBlanc towards the east or the west. Europe may be consider-ed as the western prolongation of the old continent; and thewestern parts of all continents are not only warmer at equal la-titudes than the eastern parts, but even in the zones of equalannual temperature, the winters are more rigorous, and thesummers hotter on the eastern coasts than upon the westerncoasts of the two continents. The northern part of China, like
* Political Essay on the Kingdom of New Spain, tom. iv. p. 528.† Leopold von Buch’s Travels in Lapland, tom. ii.|268| the Atlantic region of the United States, exhibits excessive cli-mates, and seasons strongly contrasted, while the coasts of NewCalifornia, and the embouchure of the Colombia, have wintersand summers almost equally temperate. The meteorologicalconstitution of these countries in the N. W. resembles that ofEurope as far as 50° or 52° of latitude; and without wishing toascribe the great revolutions of our species solely to the influ-ence of climate, we may affirm that the difference between theeastern and western shores of continents, has favoured the an-cient civilisation of the Americans of the west,—facilitated theirmigrations towards the south, and multiplied those relations witheastern Asia, which appear in their monuments, their religion,traditions, and the division of the year. In comparing the twosystems of climates, the concave and convex summits of thesame isothermal lines, we find at New York the summer of Rome and the winter of Copenhagen;—at Quebec the summerof Paris and the winter of Petersburg. In China, at Pekin for example, where the mean temperature of the year is that ofthe coasts of Britanny, the scorching heats of summer are great-er than at Cairo, and the winters as rigorous as at Upsal. The mean temperature of the year being equal to the fourthpart of the winter, spring, summer and autumnal temperatures,we shall have upon the same isothermal line of 53°6′ (12° cent.)
* Drake’s Nat. and Statist. View of Cincinnati, p. 63.|270| When we consider that the annual temperature of a place isnothing more than the numerical expression of the mean of theordinates, we may imagine an infinity of entirely dissimilarcurves, in which the twelve ordinates of the months have exact-ly the same mean. This consideration should not lead us tobelieve, that a place which has the winter of the south ofFrance, that is, where the mean temperature of winter is 44°.6,may, by the compensation of a summer and an autumn, muchless warm, have the mean temperature of Paris. It is true, thatthe constant ratio which is observed in the same parallel, be-tween the solstitial heights of the sun and the semidiurnal arcs,is differently modified by the position of a place in the centre ofa continent or upon the coast, by the frequency of certainwinds, and by the constitution of an atmosphere more or lessfavourable to the transmission of light, and of the radiating ca-loric of the earth. But these variations, which travellers haveoften exaggerated, have a maximum which nature never over-steps. It is impossible to examine the preceding table withoutobserving, that the division of the annual heat between summerand winter, follows on each isothermal line a determinate type;that the deviations of that type are contained between certain li-mits, and that they obey the same law in the zones which passby the concave or convex summits of the isothermal lines, forexample, by 58°—68° of West Long., and by 5°—7°, and 116°of East Longitude. The following table shews the oscillations, or the maxima and minima, observed in the division of the heat between the sea-sons. I have added the means of the winters and summersfound at different degrees of longitude, and under the same iso-thermal line.
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The deviations round the mean, that is, the inequality of thewinters on the same isothermal line, increase in proportion as theannual heat diminishes, from Algiers to Holland, and from Flo-rida to Pennsylvania. The winters of the curve of 68° are notfound upon that of 51°, and the winters of 51° are not met withon the curve of 42°. In considering separately what may becalled the same system of climate, for example, the EuropeanRegion, the Transatlantic Region, or that of Eastern Asia, thelimits of the variations become still more narrow. Wherever inEurope, in 40° of longitude the mean temperature rises
In tracing five isothermal lines between the parallels of Romeand Petersburg, the coldest winter presented by one of these linesis not found again on the preceding line. In this part of theglobe, those places whose annual temperature is 54° 5, have nota winter below 32°, which is already felt upon the isothermalline of 50°. If, in place of stopping at the most rigorous winterwhich each curve presents, we trace the lines of equal wintertemperature, (or the Isocheimal lines,) these lines, instead of co-inciding with the lines of equal annual heat, oscillate roundthem. As the Isocheimal lines unite points placed on differentisothermal lines, we may examine to what distance their sum-mits extend. In considering always the same system of climates,for example, the European region, we shall find that the linesof equal winter cut isothermal lines, which are 9° distant. InBelgium * (in latitude 52°, and in isothermal latitude 51°8,)and even in Scotland, (in latitude 57°, and isothermal latitude45° 5,) the winters are more mild than at Milan, (in latitude
* Throughout all Holland, 90 days of winter have a mean temperature of from36°.7 to 38°.7. At Milan, at Padua, and at Verona, the same season is only from34°.7 to 36°.7. The observations made in Belgium and Holland, offer also avery remarkable example of an equal quantity of heat distributed in the space of ayear over a vast extent of territory. The mean temperatures scarcely vary fromParis to Franecker, over 3\( \frac{1}{2} \) degrees of latitude, which, in the interior of a continent,should produce a difference of 3\( \frac{1}{4} \) degrees of annual temperature. The canal of theChannel opens towards the north. The west winds blow, therefore, over a great|272| 45° 28′, and isothermal latitude 55° 8′,) and in a great part ofLombardy. Farther to the north, in the Scandinavian Penin-sula, we meet with three very different systems of climate, viz.1. The region of the west coasts of Norway to the west of themountains. 2. The region of the eastern coasts of Sweden, tothe east of the mountains. And, 3. The region of the westcoasts of Finland, along the Gulf of Bothnia. Baron Von Buchhas made us acquainted with the atmospherical constitution ofthese three different regions, in which the slowest increase ofthe winter cold is felt from Drontheim to the North Cape,on the west and north-west coasts. At the Isle of Mageroe,(in north lat. 82°,) at the northern extremity of Europe, underthe parallel of 71°, the winters are still 7°.2 milder than at StPetersburg, (in north lat. 38°.8,) but the mean heat of thesummers never reaches that of the winters of Montpellier, (innorth lat. 59°.4). At the Faroe Isles, under 62° of north lat.the lakes are very seldom covered with ice, and to so temperatea winter succeeds a summer, during which snow often falls uponthe plains. Nowhere without the tropics is the division of theannual heat among the seasons more equal. In the temperatezone, under parallels nearer to our own, Ireland presents an ex-
part of the ocean, and during a long rainy winter, with the sky almost alwaysclouded, the surface of the earth is less cooled by radiation than farther to the east,in the interior of the country, where the atmosphere is pure and dry.
The mean duration of the observations at each place is from eight to nineyears, and 52,000 partial observations have been employed to obtain nine meantemperatures. A similar harmony in the results is also found in Lombardy.
|Spaltenumbruch|
|Spaltenumbruch|
H.
|273| ample still more striking of the union of very mild winters,with cold and moist summers. Notwithstanding a difference of4° of latitude, the winters there are as mild as in Britain, whilethe mean temperature of the summers is three degrees less.This is the true maritime climate. The month of August,which on the same isothermal line, in the east of Europe *, (inHungary) has the temperature of 71°.6, reaches only 60°.8 atDublin. The month of January, whose mean temperature atMilan, and in a great part of Lombardy, is only 35°.6, rises inIreland to 5°.4, and 7°.2. On the coasts of Glenarm, also (innorth lat. 54° 56′,) under the parallel of Konigsberg, themyrtle vegetates with the same strength as in Portugal †. Itscarcely freezes there in winter, but the heat of summer is notcapable of ripening the vine.
These examples are sufficient to prove, that the isocheimallines deviate much more than the isothermal lines from the ter-restrial parallels. In the system of European climates, the lati-tudes of two places that have the same annual temperature can-not differ more than from 4° to 5°, while two places whose meanwinter temperature is the same, may differ more than 9° or 10in latitude. The farther we advance to the east, the more ra-pidly do these differences increase.
The lines of equal summer, or isotheral curves, follow a di-rection exactly contrary to the isocheimal lines. We find thesame summer temperature at Moscow, in the centre of Russia,and towards the mouth of the Loire, notwithstanding a differ-ence of 11° of latitude. Such is the effect of the radiation ofthe earth on a vast continent deprived of mountains. It is suf-ficiently remarkable, that the inflexions of the isothermal lines,and the division of lands and seas are such upon the globe,that every where in North America, in Europe, and in EasternAsia, the mean temperature of the summers does not denotemore than 36° in the parallels of from 45° to 47°. The samecauses which in Canada, and in the north of China, sink thecurves of equal annual heat, where the isothermal lines (those of
* Wahlenberg, Flora Carpath. p. 90.† Irish Transactions, tom. viii. p. 116, 203, 269.|274| 51°.8, and 53°.6,) corresponding to the parallels of 45° and 47°,tend to raise the lines of equal summer or the isotheral curves. However great be the influence of the unequal division of theheat between the seasons, on the physical condition of nations, onthe developement of agricultural industry, and the selectionof plants for culture, I would not recommend the tracing up-on the same chart the isothermal lines, and the winter and sum-mer curves. This combination would not be more fortunatethan the lines of declination, inclination, and equal intensity ofthe magnetic forces, which, however, all depend upon one ano-ther. Instead of multiplying the intersection of the curves, itwill be sufficient to add to the isothermal lines, near their sum-mits, the indication of the mean temperatures of summer andwinter. In this way, by following the line of 50°, we shall findmarked in America, to the west of Boston, \( \left(\frac{30^\circ.2}{73^\circ.4}\right) \), in Eng-land \( \left(\frac{37^\circ.4}{62^\circ.6}\right) \), in Hungary \( \left(\frac{31^\circ.1}{69^\circ.8}\right) \), and in China \( \left(\frac{23^\circ.0}{78^\circ.8}\right) \). (To be continued.)
|23|
After what has already been stated respecting the limits be-tween which the annual heat divides itself on the same isother-mal curve, it will be seen how far we are authorised to say, thatthe Coffee-tree, the Olive, and the Vine, in order to be produc-tive, require mean temperatures of 64°.4; 60°.8, and 53°.6 Fahr.These expressions are true only of the same system of climate, forexample, of the part of the Old World which stretches to the westof the meridian of Mont Blanc; because in a zone of small extentin longitude, while we fix the annual temperatures, we determinealso the nature of the summers and the winters. It is known like-wise, that the olive, the vine, the varieties of grain, and the fruit-trees, require entirely different constitutions of the atmosphere.Among our cultivated plants, some, slightly sensible of the ri-gours of winter, require very warm but not long summers; othersrequire summers rather long than warm; while others, again, in-different to the temperature of summer, cannot resist the greatcolds of winter. Hence, it follows, that, in reference to the cultureof useful vegetables, we must discuss three things for each cli-mate,—the mean temperature of the entire summer,—that ofthe warmest month,—and that of the coldest month. I havepublished the numerical results of this discussion in my Prole-gomena de Distributione Geographica Plantarum, secundumCœli Temperiem; and I shall confine myself at present to thelimits of culture of the olive and the vine. The olive is cul-tivated in our continent between the parallels of 36° and 44°,wherever the annual temperature is from 62°.6 to 58°.1, wherethe mean temperature of the coldest month is not below from41°.0 to 42°.8, and that of the whole summer from 71°.6 to 73°.4 *.In the New World, the division of heat between the seasons issuch, that on the isothermal line of 58°.1, the coldest month is
* In cases like the present, we have not used the round numbers of Fahrenheit,as is done in the original with the Centigrade scale, but have given the real valueof the degrees used by the author, that his exact numbers may always be ascertain-ed.—Ed. |24| 35°.6, and that the thermometer sometimes sinks there even du-ring several days from 14° to 10°.4. The region of potable winesextends in Europe between the isothermal lines of 62°.6 and 50°,which correspond to the latitudes of 36° and 48°. The culti-vation of the vine extends, though with less advantage, even tocountries whose annual temperature descends to 48°.2 and to47°.48; that of winter to 33°.8, and that of summer to 66°.2and 68°. These meteorological conditions are fulfilled in Eu-rope as far as the parallel of 50°, and a little beyond it. InAmerica, they do not exist farther north than 40°. They havebegun, indeed, some years ago to make a very good red wineto the west of Washington, beyond the first chain of mountains,in the valleys which do not extend beyond 38° 54′ of Lat. On theContinent of Western Europe, the winters, whose mean tempe-rature is 32°, do not commence till on the isothermal lines of48°.2 and 50°, in from 51° to 52° of latitude; while in America,we find them already on the isothermal lines of from 51°.8 to53°.6, under from 40° to 41° of latitude. If, instead of considering the natural inflexions of the isother-mal lines, that is to say, those that propagate themselves pro-gressively at great intervals of longitude, we direct our atten-tion to their partial inflexions, or to particular systems of cli-mates occupying a small extent of country, we shall still findthe same variations in the division of the annual heat betweenthe different seasons. These partial inflexions are most remark-able, 1st, In the Crimea, where the climate of Odessa is contrastedwith that of the S.W. shores of the Chersonesus, sheltered bymountains, and fit for the cultivation of the olive and the orangetree. 2dly, Along the Gulf of Genoa, from Toulon and the HieresIsles to Nice and Bordighera, (Annales du Museum, tom. xi.p. 219.), where the small maritime palm-tree, Chamærops, grows wild, and where the date-tree is cultivated on a largescale, not to obtain its fruit, but the palms or etiolated leaves. 3dly, In England, on the coast of Devonshire, where the portof Salcombe has, on account of its temperate climate, been call-ed the Montpellier of the North, and where (in South Hams) theMyrtle, the Camellia Japonica, the Fuchsia coccinea, and the |25| Buddleia globosa *, pass the winter in the open ground, andwithout shelter. 4thly, In France, on the western coasts of Normandy and Brit-tany. In the Department of Finisterre, the arbutus, the pome-granate-tree, the Yucca gloriosa and aloifolia, the Erica Medi-terranea, the Hortensia, the Fuchsia, the Dahlia, resist in openground the inclemency of a winter which lasts scarcely fifteen ortwenty days, and which succeeds to a summer by no meanswarm. During this short winter, the thermometer sometimesfalls to 17°.6. The sap ascends in the trees from the month ofFebruary; but it often freezes even in the middle of May.The Lavatera arborea is found wild in the isle of Glenans, andopposite to this island, on the continent, the Astragalus Bajon-ensis, and the Laurus nobilis †. From observations made in Brittany for twelve years, atSt Malo, at Nantes, and at Brest, the mean temperature of thepeninsula appears to be above 56°.3. In the interior of France,where the land is not much elevated above the sea, we must de-scend 3° of latitude in order to find an annual temperature likethis. It is known from the researches of Arthur Young ‡, that inspite of the great rise of the two isothermal lines of 53°.6 and55°.4 on the western coast of France, the lines of culture (thoseof the olive, and of the maize and vine,) have a direction || quiteopposite, from S.W. to N.E. This phenomenon has been as-cribed §, with reason, to the low temperature of the summers
* Knight, Trans. Hort. Soc. vol. i. p. 32. In 1774, an Agave flowered atSalcombe, after having lived twenty-eight years without being covered in winter.On the coast of England, the winters are so mild, that orange trees are seen onespaliers, which are sheltered, as at Rome, only by means of a matting.—H.† Bonnemaison, Geogr. Botan. du Depart. du Finisterre, (Journal de Botan. tom. iii. p. 118.)‡ Travels in France, vol. ii. p. 91.|| The line which limits the cultivation of the vine, extends from the embou-chure of the Loire and of the Vilaine, by Pontoise, to the confluence of the Rhineand the Moselle. The line of the olive trees commences to the west of Narbonne,passes between Orange and Montelimart, and carries itself to the N.E. in the di-rection of the Great St Bernard.—H.§ Decandolle, Flor. Franç. 3d edit. tom. ii. pl. viii. xi. Lequinio, Voy. dans.le Jura, tom. ii. p. 84.—91.|26| along the coast; but no attempt has been made to reduce to nu-merical expressions the ratios between the seasons in the inte-rior and on the coast. In order to do this, I have chosen eight places, some of which lie under the same geographic parallels,and others in the prolongation of the same isothermal line. Ihave compared the temperatures of winter, of summer, and ofthe warmest months; for a summer of uniform heat excites lessthe force of vegetation, than a great heat, preceded by a cold sea-son. The terms of comparison have been along the Atlantic;the coasts of Brittany, (from St Malo and St Brieux to Vannesand Nantes); the sands of Olonne; the Isle of Oleron; theembouchure of the Garonne and Dax, in the department of theLandes; and in the interior, corresponding to the same parallel,Chalons sur Marne, Paris, Chartres, Troyes, Poitiers, andMontauban. Farther south, from 44\( \frac{1}{2} \)° of Lat. the comparisonsbecome incorrect, because France, locked between the Oceanand the Mediterranean, presents, along this last basin, in thefine region of the olives, a system of climate of a particularkind, and very different from that of the western coast.
|27|
These results are deduced from 127,000 observations, madewith sixteen thermometers, of, no doubt, unequal accuracy. Insupposing, on the theory of probabilities, that in such a numberof observations, the errors, in the construction and exposure ofthe instruments, and in the hours of observation, will, in a greatmeasure, destroy one another, we may determine, by interpola-tion, either under the same parallel, or upon the same isother-mal line, the mean winters and summers of the interior and ofthe coast of France. This comparison gives,—
As the isothermal lines rise again towards the western coastsof France; that is to say, as the mean temperature of the year be-comes there greater than under the same latitude in the interior ofthe country, we ought to expect, that in advancing from east towest under the same parallel, the heat of the summers would notdiminish. But the rising, again, of the isothermal lines, and theproximity of the sea, tend equally to increase the mildness of thewinters; and each of these two causes acts in an opposite mannerupon the summers. If the division of the heat between these sea-sons was equal in Brittany and in Orleannois, in the climate of thecoast, and the continental climates, we ought to find the wintersand summers warmer in the same latitude along the coast. Infollowing the same isothermal lines, we readily observe, in thepreceding table, that the winters are colder in the interior of thecountry, and the summers more temperate upon the coasts. Theseobservations confirm in general the popular opinion respectingthe climate of coasts; but in recollecting the cultivation and thedevelopement of vegetation on the coasts and in the interior ofFrance, we should expect differences of temperature still moreconsiderable. It is surprising that these differences between the
|28| winter and the summer should not exceed 1°.8, or nearly aquarter of the difference between the mean temperature of thewinters or the summers of Montpellier and Paris. In speak-ing of the limits of the cultivation of plants upon mountains, Ishall explain the true cause of this apparent contradiction. Inthe mean time, it may be sufficient to remark, that our meteo-rological instruments do not indicate the quantity of heat,which, in a clear and dry state of the air, the direct light pro-duces in the more or less coloured parenchyma of the leavesand fruits. In the same mean temperature of the atmosphere,the developement of vegetation is retarded or accelerated, ac-cording as the sky is foggy or serene, and according as the surfaceof the earth receives only a diffuse light, during entire weeks,or is struck by the direct rays of the sun. On the state ofthe atmosphere, and the degree of the extinction of light, de-pend, in a great measure, those phenomena of vegetable life,the contrasts of which surprise us in islands, in the interior ofcontinents, in plains, and on the summit of mountains. If weneglect these photometrical considerations, and do not appre-ciate the production of heat in the interior of bodies, and theeffect of nocturnal radiation in a clear or a cloudy sky, we shallhave some difficulty in discovering, from the numerical ratiosof the observed summer and winter temperatures of Paris andLondon, the causes of the striking difference which appears inFrance and England in the culture of the vine, the peach, andother fruit-trees *.
When we study the organic life of plants and animals, wemust examine all the stimuli or external agents which modifytheir vital actions. The ratios of the mean temperatures of themonths are not sufficient to characterise the climate. Its in-fluence combines the simultaneous action of all physical causes;and it depends on heat, humidity, light, the electrical tension ofvapours, and the variable pressure of the atmosphere. It is thelast cause which, on the tops of mountains, modifies the perspi-ration of plants, and even increases the exhaling organs. Inmaking known the empirical laws of the distribution of heat
* Young’s Travels in France, vol. ii. p. 195.|29| over the globe, as deducible from the thermometrical variationsof the air, we are far from considering these laws as the onlyones necessary to resolve all the problems of climate. Most ofthe phenomena of nature present two distinct parts, one whichmay be subjected to exact calculation, and another which can-not be reached but through the medium of induction and ana-logy. Having considered the division of heat between winter andsummer on the same isothermal line, we shall now point out thenumerical ratios between the mean temperature of spring andwinter, and between that of the whole year and the warmestmonth. From the parallel of Rome to that of Stockholm, andconsequently between the isothermal lines of 60°.8 and 41°,the difference of the months of April and May is everywhere10°.8 or 12°.6, and all the successive months are those whichpresent the most rapid increase of temperature. But, as innorthern countries, in Sweden, for example, the month ofApril is only 37°.4, the 10°.8 or 12°.6 which the month ofMay adds *, necessarily produces there a much greater ef-fect on the developement of vegetation than in the south of Eu-rope, where the mean temperature of April is from 53°.6 to55°.4. It is from an analogous cause, that in passing from theshade to the sun, either in our climates in winter, or betweenthe tropics on the back of the Cordilleras, we are more affectedby the difference of temperature than in summer and in theplains, though in both cases the thermometrical difference is thesame, for example from 5°.4 to 7°.2. Near the polar circle, theincrease of the vernal heat is not only more sensible, but it ex-tends equally to the month of June. At Drontheim, the tem-peratures of April and May, like those of May and June, differnot 10°.8 or 12°.6, but 14°.4 or 16°.2. In distinguishing upon the same isothermal line the placeswhich approach its concave or convex summits, in the same sys-
* In calculating for Europe, from 46° to 48° of Lat. for ten years the meantemperatures of every ten days, we find, that the decades which succeed one another,differ near the summits of the annual curve only 1°.44, while the differences risein autumn from 3°.6 to 5°.4, and in spring from 5°.4 to 7°.2.—H.|30| tem of climates in the northern and southern regions, we shallfind, 1st, That the increase of the vernal temperature is great,(from 14°.4 or 16°.2, in the space of a month), and equally pro-longed, wherever the division of the annual heat between theseasons is very unequal, as in the north of Europe, and in thetemperate part of the United States. 2dly, That the vernal increase is great, (at least above 9° or10°.8), but little prolonged, in the temperate part of Europe. 3dly, That the increase of the vernal temperature is small,(scarcely 7°.2), and equally prolonged, wherever there is an in-sular climate. 4thly, That in every system of climates, in the zones contain-ed between the same meridians, the vernal increase is smaller,and less equally prolonged, in low than in high latitudes. The isothermal zone from 53°.6 to 55°.4, may serve as an ex-ample for confirming these different modifications of spring. InEastern Asia, near the concave summit, the differences of tem-perature between the four months of March, April, May andJune, are very great, and very equal, (15°.7, 13°.3, and 13°.9).In advancing westward towards Europe, the isothermal linerises again, and in the interior of the country, near the convexsummit, the increase is still greater, but little prolonged; that isto say, that of the four months which succeed one another, thereare only two whose difference rises to 13°: they are 9°.4; 13°.3;4°.1. Farther west, on the coasts, the differences become smalland equal, viz. 3°.6; 6°.5; 5°.6. In crossing the Atlantic, weapproach the western concave summit of the isothermal line of53°.6. The increase of vernal temperature shews itself anew,and almost as great, and as much prolonged, as near the Arcticconcave summit. The differences of the four months are 10°.4;13°.9; and 10°.8. In the curve of annual temperature, thespring and autumn mark the transitions from the minimum andthe maximum. The increments are naturally slower near the sum-mits than in the intermediate part of the curve. Here they aregreater, and of longer continuance, in proportion to the diffe-rence of the extreme ordinates. The autumnal decrease of tem-perature is less rapid than the vernal increase, because the sur- |31| face of the earth acquires the maximum of heat slower than theatmosphere, and because, in spite of the serenity of the air whichprevails in autumn, the earth loses slowly, by radiation, the heatwhich it has acquired. The following Table will shew howuniform the laws are which I have just established.
|32|
In all places whose mean temperature is below 62°.6, the re-vival of nature takes place in spring, in that month whose meantemperature reaches 42°.8 or 46°.4. When a month rises to,
* Cotte, Meteorologie, p. 448.—Wahlenberg, Flor. Lap. Pl. 51.† Playfair, Edin. Trans, vol. v. p. 202.— Wahlenberg in Gilbert’s Annalen, tom. xli. p. 282.|33|
|34|
In the system of European climates, from Rome to Upsal,between the isothermal lines of 59° and 41°, the warmest monthadds from 16°.2 to 18° to the mean temperature of the year.Farther north, and also in eastern Asia, and in America, wherethe isothermal lines bend towards the equator, the incrementsare still more considerable.
As two hours of the day indicate the temperature of the wholeday, there must also be two days of the year, or two decades,whose mean temperature is equal to that of the whole year.From the mean of ten observations, this temperature of the yearis found at Buda in Hungary from the 15th to the 20th ofApril, and from the 18th to the 23d of October. The ordinatesof the other decades may be regarded as functions of the meanordinates. In considering the temperatures of entire months, wefind, that to the isothermal line of 35°.6, the temperature of themonth of October coincides (generally within a degree) withthat of the year. The following Table proves that it is not themonth of April, as Kirwan affirms, (Estimate, &c. p. 166.),that approaches nearest to the annual temperature.
|Spaltenumbruch|
|Spaltenumbruch|
As travellers are seldom able to make observations for givingimmediately the temperature of the whole year, it is useful toknow the constant ratios which exist in each system of climates,between the vernal and autumnal temperatures, and the annualtemperature.
|35|
The quantity of heat which any point of the globe receives,is much more equal during a long series of years than we wouldbe led to believe from the testimony of our sensations, and thevariable product of our harvests. In a given place, the num-ber of days during which the N.E. or S.W. winds blow, pre-serve a very constant ratio, because the direction and the forceof these winds, which bring warmer or colder air, depend up-on general causes,—on the declination of the sun,—on the con-figuration of the coast,—and on the lie of the neighbouringcontinent. It is less frequently a diminution in the mean tem-perature, than an extraordinary change in the division of theheat between the different months, which occasions bad harvests.By examining between the parallels of 47° and 49° a series ofgood meteorological observations, made during ten or twelveyears, it appears, that the annual temperatures vary only from1°.8 to 2°.7; those of winter from 3°.6 to 5°.4; those of themonths of winter from 9° to 10°.8. At Geneva, the mean tem-peratures of twenty years were as follows:
If, in our climates, the thermometrical oscillations are asixth part of the annual temperature, they do not amount toone twenty-fifth part under the tropics. I have computed thethermometrical variations, during eleven years, at Paris, forthe whole year, the winter, the summer, the coldest month, thewarmest month, and the month which represents most accurate-ly the annual mean temperature; and the following are the re-sults which I obtained:
|36|
At Geneva, the mean temperatures of the summers were,from 1803 to 1809,—
M. Arago has found, that in the two years 1815 and 1816,the last of which was so destructive to the crops in a great partof France, the difference of the mean annual temperature wasonly 2°, and that of the summer 3°.2. The summer of 1816at Paris was 59°.9, 4°.7 below the mean of the former. From1803 to 1813, the oscillations round the mean did not go be-yond — 2°.9, and +3°4.
In comparing places which belong to the same system of cli-mates, though more than eighty leagues distant, the variationsseem to be very uniform, both in the annual temperature andthat of the seasons, although the thermometrical quantities arenot the same.
|37|
(To be continued in next Number.)
|262|
All the ratios of temperature which we have hitherto fixed,belong to that part of the lower strata of the atmosphere whichrests on the solid surface of the globe in the northern hemi-sphere. It now remains for us to discuss the temperature of thesouthern hemisphere. In few parts of natural philosophy, havenaturalists differed so widely in opinion. From the beginningof the 16th century, and the first navigations round Cape Horn,an idea prevailed in Europe, that the southern was considerablycolder than the northern hemisphere. Mairan and Buffon *
combated this opinion by inaccurate reasonings of a theoreticalnature. Æpinus † established it anew. The discoveries ofCook made known the vast extent of ice round the South Pole;but the inequality in the temperature of the two hemisphereswas then exaggerated. Le Gentil, and particularly Kirwan ‡,had the merit of having first demonstrated, that the influence ofthe circumpolar ice extended much less into the temperate zonethan was generally admitted. The less distance of the sun fromthe winter solstice, and his long continuance in the northernsigns, act in an opposite manner ║ on the heat in the two hemi-spheres; and as (after the theorem of Lambert) the quantity oflight which a planet receives from the sun, increases in propor-tion to the true anomaly, the inequality in the temperature ofthe two hemispheres is not the effect of unequal radiation. Thesouthern hemisphere receives the same quantity of light; butthe accumulation of heat in it is less §, on account of the emis-sion of the radiant heat which takes place during a long winter.This hemisphere being also in a great measure covered with
* Theorie de la Terre, tom. i. p. 312.—Mémoires de l’Acad. 1765, p. 174.† De Distributione Caloris, 1761.‡ Estimate, &c. p. 60.—Irish Trans. vol. viii. p. 423.—Le Gentil, Voyagedans l’Inde, vol. i. p. 73.║ Mairan, Mem. Acad. 1765, p. 166.—Lambert, Pyrometrie, p. 310.Prevost, De la Chaleur Rayonnante, 1809, p. 329. & 367. § 280,—306.|263| water, the pyramidal extremities of the continents have there anirregular climate. Summers of a very low temperature are suc-ceeded, as far as 50° of south latitude, by winters far from ri-gorous. The vegetable forms also of the torrid zone, the ar-borescent ferns, and the orchideous parasites, advance towards38° and 42° of S. Latitude. The small quantity of land * in the southern hemispheres, contributes not only to equalise theseasons, but also to diminish absolutely the annual temperatureof that part of the globe. This cause is, I think, much moreactive than that of the small eccentricity of the earth’s orbit.The continents during summer radiate more heat than the seas,and the ascending current which carries the air of the equinoc-tial and temperate zones towards the circumpolar regions, actsless in the southern than in the northern hemisphere. Thatcap of ice which surrounds the pole to the 71st and 68th degreeof south latitude, advances more towards the equator, wheneverit meets a free sea; that is, wherever the pyramidal extremitiesof the great continents are not opposite to it. There is reasonto believe, that this want of dry land would produce an ef-fect still more sensible, if the division of the continents was asunequal in the equinoctial as in the temperate zones †. Theory and experience prove, that the difference of tempera-ture between the two hemispheres, cannot be great near thelimit which separates them ‡. Le Gentil had already observed,that the climate of Pondicherry is not warmer than that of Ma-dagascar at the Bay of Antongel in 12° of S. Lat. Under theparallels of 20 the Isle of France has the same annual tempera-ture, viz. 80°.1, as Jamaica and St Domingo. The IndianSea between the east coasts of Africa, the Isles of Sonde andNew Holland, form a kind of gulf which is shut up to the northby Arabia and Hindostan. The isothermal lines there appearto go back to the South Pole; for farther to the west in the opensea between Africa and the New World, the cold of the south-ern hemisphere already causes itself to be felt from the 22d de-gree, on account of its insulated mountains and particular loca-
* The dry lands in the two hemispheres are in the ratio of 3 to 1.† The dry lands between the tropics, are in the two hemispheres as 5 to 4,and without the tropies as 13 to 1.‡ Prevost, p. 343.|264| lities. 1 shall not mention the island of St Helena, Lat. 15°55′ whose mean temperature, according to the observations of M.Beatson, at the sea side, does not exceed 71°6 or 73°4. It isthe eastern coast of America, which, in the observations of a Por-tuguese astronomer, M. Benito Sanchez Dorta *, present us withthe S. Lat. of 22° 54′, almost at the limit of the equinoctialregion with a plan, of which we know the climate by more than3500 thermometrical and barometrical observations made everyyear, to ascertain the horary variations in the heat and pressureof the air. The mean temperature of Rio Janeiro is only 74°.3,whilst, notwithstanding the north winds which bring the coldair of Canada during winter into the Gulf of Mexico, the meantemperatures of Vera Cruz, (Lat. 19° 11′,) and of the Havannah,(Lat. 23° 10′,) are 77°.9. The differences of the two hemis-pheres become more sensible in the warmest months.
The great equality in the divısion of the annual heat in34° of N. and S. Lat. is very surprising. If we attend to thethree continents of New Holland, Africa and America, we shallfind, that the mean temperature of Port Jackson, (Lat. 33° 51′,)is, after the observations of MM. Hunter, Peron, and Freyci-net, ‒ ‒ ‒ 66°.7
That of the Cape of Good Hope, (Lat. 33° 53′,) 66 9
That of the city of Buenos Ayres, (Lat. 34° 36′,) 67 5
In the northern hemisphere 60°.8 or 69°.8 of annual tem-perature corresponds to the same latitude in the northernhemisphere, according as we compare the American system ofclimates † or the Mediterranean one;—the concave or the convex
* Mem. de l’Acad. de Lisbonne, tome ii. p. 348. 369.†
|265| parts of the isothermal lines. At Port Jackson, where the ther-mometer descends sometimes below the freezing point, the warm-est month is 77°.4, and the coldest 56°.8. We find here thesummer of Marseilles and the winter of Cairo *. In Louisiana2\( \frac{1}{2} \) of Lat. nearer the Equator, the warmest month is 79°.7,and the coldest 46°.9. In Van Diemen’s Land, correspondingnearly in latitude to Rome, the winters are more mild than atNaples; but the coldness of the summers † is such, that themean temperature of the month of February appears to bescarcely 64°.4, or 66°.2, whilst at Paris, under a latitude moredistant from the Equator by 7°, the mean temperature of themonth of August is also from 64°.4 to 66°.2′, and at Romeabove 77°. Under the parallel of 51° 25′ south, the meantemperature of the Malouine Isles is well ascertained to be 47°.3.At the same Lat. N. we find the mean temperature in Eu-rope from 50° to 51°.8, and in America scarcely from 35°.6to 37°.4. The warmest and the coldest months are at London66°.2 and 35°.6; at the Malouine Isles 55°.8 and 37°.4.At Quebec, the mean temperature of the water is 14°; at theMalouine Isles 39°.6, though those isles are 4° of Lat. fartherfrom the Equator than Quebec. These numerical ratios prove,that, to the parallels of 40° and 50°, the corresponding isother-mal lines are almost equally distant from the Pole in the twohemispheres; and that, in considering only the system of trans-atlantic climates between 70° and 80° of W. Long., the meantemperatures of the year, under the corresponding geographicalparallels, are even greater in the southern than in the northernhemisphere.
The division of the heat between the different parts of theyear, gives a particular character to southern climates. In the
*
† In Van Diemen’s Land the thermometer descends in February, in the morn-ing, to 45°.5. The mean of mid-day is 60°.8. At Paris it is in August 73°.4.In Van Diemen’s Land, in February the mean of the maxima is 78°8.; of theminima 54°.5. At Rome these means are 86° and 64°.5.—D’Entrecasteaux,
Voyage, tom. i. p. 205. and 542.|266| southern hemisphere on the isothermal lines of 46°.4 and 50°.0,we find summers which in our hemisphere belong only tothe isothermal lines of 35°.6 and 40°. The mean temperatureis not precisely known beyond 51° of S. Lat. Navigators donot frequent those regions when the sun is in the northern signs,and it would be wrong to judge of the rigour of winter, from thelow temperature of the summer. The eternal snows which in 71°of N. Lat. support themselves at the height of 2296 feet abovethe sea, descend even into the plains, both in South Georgia *
and in Sandwich Land in 54° and 58° of S. Lat. But thesephenomena, however striking they may appear, do not by anymeans prove that the isothermal line of 32° is 5° nearer theSouth Pole than the North Pole. In the system of transatlan-tic climates, the limit of eternal snow is not at the same altitudeas in Europe; and in order to compare the two hemispheres, wemust take into account the difference of longitude. Besides, anequal altitude of the snows, does not by any means indicate anequal mean temperature of the year. This limit depends par-cularly † on the coldness of summer, and this again on the quickcondensations of the vapour caused by the passage of the float-ing ice. Near the poles the foggy state of the air diminishes insummer the effect of the solar irradiation, and in winter that ofthe radiation of the globe. At the Straits of Magellan, MM.Churruca and Galeano have seen snow fall in 53° and 54° ofS. Lat. in the middle of summer; and though the day was 18hours long, the thermometer seldom rose above 42°.8 or 44°.6and never above 51°.8.
The inequal temperature of the two hemispheres, which, aswe have now proved, is less the effect of the eccentricity of the
* It is the more surprising to find in the Island of Georgia snow on the banksof the ocean, because 2° 39′ nearer the Equator at the Malouine Isles, the meantemperature of the summers is 53°.1, or 9° greater than at the point in ourhemisphere in 71° of Lat. where the limit of perpetual snow exists at 2296 feetof absolute elevation. But we must recollect, 1st, That the Malouine Isles arenear a continent which is heated in summer; 2d, That Georgia is covered withmountains, and is placed not only in a sea open to the north, but under the influ-ence of the perennial ices of Sandwich Land; and, 3dly, That in Lapland, 20° ofLat. produce in certain local circumstances 10°.8 of difference in the tempera-tures of the summers.† Baron Von Buch’s Travels in Lapland, vol. ii. p. 393,—420.|267| earth’s orbit, than of the unequal division of the continents, de-termines * the limit between the N. E. and S. E. Trade Winds.But as this limit is much more to the north of the Equator inthe Atlantic Ocean, than in the South Sea, we may concludethat, in a region between 130° and 150° of W. Long. the dif-ference of temperature between the two hemispheres, is less greatthan farther to the east in 20° or 50° of longitude. It is in-deed under this region in the Great Ocean, that, as far as theparallel of 60°, the two hemispheres are equally covered withwater, and equally destitute of dry land, which, radiating theheat during summer, sends the warm air towards the poles. Theline which limits the N. E. and S. E. Trade Winds, approachesthe Equator, whereas the temperature of the hemispheres is dif-ferent; and if, without diminishing the cold of the southern at-mosphere, we could increase the inflexion of the isothermal linesin the system of transatlantic climates, we should meet the S. E.winds in 20° and 50° of W. Long. to the north, and in 130°and 150° of W. Long. to the south of the Equator †. The low strata of the atmosphere which rest upon the aque-ous surface of the globe, receive the influence of the tempera-ture of the waters. The sea radiates less absolute heat thancontinents; it cools the air upon the sea, by the effect of eva-poration; it sends the particles of water cooled and heavier to-wards the bottom; and it is heated again, or cooled, by the cur-rents directed from the Equator to the Poles, or by the mixtureof the superior and inferior strata on the sides of banks. It is from these causes combined, that, between the tropics,and perhaps as far as 30° of Lat., the mean temperatures of theair next the sea, are 3°.6 or 5°.4 lower than that of the conti-nental air. Under high latitudes, and in climates where theatmosphere is coolest in winter, much below the freezing point,the isothermal lines rise again towards the Poles, or becomeconvex when the continents pass below the seas ‡. With respect to the temperature of the ocean, we must dis-tinguish between four very different phenomena. 1st, The tem-
* Prevost, Journ. de Phys. tom. xxxviii. p. 369.—Irish Trans. vol. viii, p. 374.† Humboldt’s Relat. Histor. tom. i. p. 225, 237.‡ Id. p. 67, 230. 242.|268| perature of the water at the surface corresponding to differentlatitudes, the ocean being considered at rest, and destitute ofshallows and currents. 2d, The decrease of heat in the super-imposed strata of water. 3d, The effect of billows on the tem-perature of the surface water. 4th, The temperature of cur-rents, which impell with an acquired velocity, the waters of ourzone across the immoveable waters of another zone. The re-gion of warmest waters no more coincides with the Equator, thanthe region in which the waters reach their maximum of saltness.In passing from one hemisphere to another, we find the warmestwaters between 5° 45′ of N. Lat., and 6° 15′ of S. Lat. Per-rins found their temperature to be 82°.3; Quevedo 83°.5;Churruca 83°.7, and Rodman 83°.8. I have found them inthe South Sea to the east of the Galapagos Isles 84°.7. The va-riations and the mean result do not extend beyond 1°.3. Itis very remarkable that in the parallel of warmest waters, thetemperature of the surface of the sea is from 3°.6 to 5°.4higher than that of the superincumbent air. Does this differencearise from the motion of the cooled particles towards the bot-tom, or the absorption of light, which is not sufficiently compen-sated by the free emission of the radiant coloric. As we ad-vance from the Equator to the Torrid Zone, the influence ofthe seasons on the temperature of the surface of the sea be-comes very sensible; but as a great mass of water follows veryslowly the changes in the temperature of the air, the means ofthe months do not correspond at the same epochs in the oceanand in the air. Besides, the extent of the variations is less inthe water than in the atmosphere, because the increase or de-crease in the heat of the sea takes place in a medium of varia-ble temperature, so that the minimum and the maximum of theheat which the water reaches, are modified by the atmospheri-cal temperature of the months which follow the coldest of thewarmest months of the year. It is from an analogous cause,that in springs which have a variable temperature, for example,near Upsal *, the extent of the variations of temperature is only19°.8, while the same extent in the air from the month of Janu-ary to August, is 39°.6. In the parallel of the Canary Islands,
* Gilbert’s Annalen, 1812, p. 129.|269| Baron Von Buch found the minimum of the temperature of thewater to be 68°, and the maximum 74°.8. The temperatureof the air in the warmest of the coldest months, is, in that quar-ter, from 64°.4 to 75°.2. In advancing towards the north,we find still greater differences of winter temperature betweenthe surface of the sea and the superincumbent air. The cooledparticles of water descend till their temperature reaches 39°.2;and hence in 46° and 50° of Lat. in the part of the Atlanticwhich is near Europe, the maximum and minimum of heat are In the water at its surface, 68°.0 and 41°.9 In the air from the mean of warmest and coldest months, 66.2 and 35.6 The excess in the mean temperature of the water over that ofthe air, attains its maximum beyond the polar circle, where thesea does not wholly freeze. The atmosphere is cooled to such adegree in these seas, (from 63° to 70° of Lat., and 0° of Long.)that the mean temperature of several months of winter descendon the continents to 14° and 10°.4, and on the coasts to 23°and 21°.2, while the temperature of the surface of the sea isnot below 32° or 30°.2. If it is true, that even in those highlatitudes the bottom of the sea contains strata of water which,at the maximum of their specific gravity, have 39°.2 or 41° ofheat, we may suppose that the water at the bottom contributesto diminish the cooling at the surface. These circumstanceshave a great influence on the mildness of countries in continentsseparated from the Pole by an extensive sea. Hitherto we have attended to the distribution of heat on thesurface of the globe at the level of the sea. It only remains forus to consider the variations of temperature in the higher re-gions of the atmosphere, and in the interior of the earth. The decrease of heat in the atmosphere, depends on severalcauses, the principle of which, according, to Laplace and Les-lie *, is the property of the air to increase its capacity for heat byits rarefaction. If the globe was not surrounded by a mixtureof elastic and aëriform fluids, it would not be sensibly colder atthe height of 8747 yards than at the level of the sea. As each
* Essay on Heat and Moisture, p. 11.; and Geometry, p. 495.|270| part of the globe radiates in every direction, the interior of aspherical envelope which would rest on the top of the highestmountains, would receive the same quantity of radiant heat asthe lower strata of the atmosphere. The heat, it is true, willbe spread over a surface a little greater; but the difference oftemperature will be insensible, since the radius of the sphericalenvelope will be to that of the earth as 1.001 to 1. Considering the earth as surrounded with an atmosphericalfluid, it is obvious, that the air heated at its surface will ascend,dilate itself, and be cooled, either by dilatation, or, by a morefree radiation across the other strata that are equally rarified.These are the ascending and descending currents, which keepup the decreasing temperature of the atmosphere *. The cold of mountains is the simultaneous effect, 1st, Of thegreater or less vertical distance of the strata of air at the surfaceof the plains and of the ocean. 2d, Of the extinction of light,which diminishes with the density of the superincumbent strataof air †; and, 3d, Of the emission of radiant heat, which is fa-voured by air very dry ‡, very cold, and very clear. The meantemperature of our present plains would be lowered, if the seasshould experience a considerable diminution. The plains ofcontinents would then become plateaux, and the air which rest-ed on them would be cooled by the circumjacent strata of air,which, at the same level, would receive but a small portion ofthe heat emitted from the dry bottom of the seas. The following Table contains the results of observationswhich I have made near the Equator, on the Andes of Quito,and towards the northern extremity of the torrid zone, in theCordilleras of Mexico. These results are true means, given ei-ther by stationary observations made during several years, orby insulated observations. In these last, we have taken intoaccount the hour of the day,—the distance of the solstices,—thedirection of the wind,—and the reflection from the plains.
* Essay on Heat and Moisture, p. 11.; and Geometry, p. 495.† Humboldt on Refraction below 10°, Observ. Astron. tom. i. p. 126.‡ Wells on Dew, p. 50.|271|
|272|
The means given by the Mexican observations are a little dif-ferent from those given by the observations on the Cordilleras.When the differences and the coincidences amount to about adegree of Fahrenheit, they may be regarded as purely acciden-tal. The length of the day is more unequal in the 20th de-gree of latitude, but the perpetual snows do not descend 656feet lower than under the Equator. As the Cordilleras of NewGranada, Quito, and Peru, present a great number of pointswhere stationary observations have been made, I shall collecthere the mean temperatures which M. Caldas * and I have de-termined with some certainty, and which all belong to a zonebounded by the parallels of 10° N. and 10° S. Lat.
|Spaltenumbruch|
These thirty-two points are not insulated points, as balloonswould be if they were fixed in the atmosphere at a perpendicu-lar height of 16,400 feet. They are stations taken on the decli-vity of mountains, upon that part of the solid mass of the globewhich, in the form of a wall, rises into the higher regions of theatmosphere. These mountains, too, have at each height parti-
* I have used the mean temperature and barometrical measurements publishedat Santa Fé de Bogota by MM. Caldas and Restrepo in the Semanario del N. R. deGranada, tom. i. p. 273.; tom. i. p. 93.—341.|273| cular climates, modified by the radiation of the plateaus onwhich they stand,—upon the slope of the ground,—the naked-ness of the soil,—the humidity of the forests,—and the currentswhich descend from the neighbouring summits. Without knowing the localities themselves, the effect of dis-turbing causes will be readily seen, by comparing in the pre-ceding Table the mean temperatures which correspond to thesame elevations; and the discussion of these observations wouldprove, also, that the extent of the variations is much less than isgenerally believed. If we examine thirty-two temperatures, uponthe hypothesis that a degree of cooling corresponds to an altitudeof 200 metres (656 feet), we shall deduce the temperature of theplains (from 30°.6 to 82°.4) twenty-six times from that of elevatedplaces. For the other six deductions, the temperatures differ on-ly about 3°.6; and the errors of observation are here combinedwith the effects of localities. The air which rests on the plains ofthe Andes mixes itself with the great mass of the free atmosphere,in which there prevails under the torrid zone a surprising stabi-lity of temperature. However enormous be the mass of theCordilleras, it acts but feebly on the strata of air which are un-ceasingly renewed. On the other hand, if the plains are heatedduring the day, they radiate as much during the night; for itis principally on the plains elevated 8856 feet above the sea,that the sky is most clear and uniformly serene. At Peru, forexample, the magnificent plateau of Caxamarca, in which thewheat yields the eighteenth, and barley the sixtieth grain, hasan extent of more than twelve square leagues: it is smooth likethe bottom of a lake, and sheltered by a circular wall of moun-tains free from snow. Its mean temperature is 60°.8, yet thewheat is often frozen during the night; and in a season wherethe thermometer fell before sunrise to 46°.4, I have seen it risein the day to 77° in the shade. In the vast plains of Bogota,which are 656 feet less elevated than that of Caxamarca, themean temperature, as established by the fine observations ofMutis, is scarcely 57°.74. In comparing towns situated on elevated plains with thosewhich are placed on the declivity of mountains, I have found forthe first an augmentation of temperature, which, on account of the |274| nocturnal radiation, does not exceed from 2°.7 to 4°.14. Thisaugmentation is a little greater in the lower regions of theAndes, in those large valleys whose smooth bottoms reach theheight of from 1312 to 1640 feet, principally in the valley ofLa Madaleine, between Neiva and Honda. It is singular tofind in the middle of mountains heats which equal those of theplains, and which are more insupportable, as the air of the val-leys is almost never agitated by the winds. If we compare,however, the mean temperatures of these same places with thoseof the strata of the true atmosphere, or on the declivity of moun-tains, we shall find them only from 3°.6 to 5°.4. On these grounds, we may place some confidence on the fourresults which we have deduced from such a great number of ob-servations, for the perpendicular heights of 1000, 2000, 3000,and 4000 metres. I have confined myself to a simple arithme-tical mean, and to the fortuitous compensation of irregularities;for I could not have avoided employing an hypothesis on thedecrease of heat, if I had wished to reduce to a standardheight those heights which approach it the most. I have addedthe observations with which an intimate knowledge of localitieshas furnished me.
|275|
Between the tropics, the Cordilleras form the centre of thecivilization and industry of Spanish America. They are inha-bited to the height of 4000 metres, (13,120 feet); and a smallnumber of observations made on the back of the Andes, gives asufficiently accurate idea of the mean temperature of the year.In Europe, on the contrary, in the temperate zone, the highmountains are in general little inhabited. The descent of theisothermal line of 32°, causes to cease the cultivation of crops ofgrain, at the point where they begin in the Cordilleras. Sta-tionary habitations are rare above 2000 metres (6560 feet) ofelevation; and in order to judge with any precision of the meantemperature of the superincumbent beds of air, we must uniteat least 730 thermometrical observations made in the course ofa year *.
* Elevations of 400 metres (1312 feet) appear to have a very sensible influenceon the mean temperature, even when great portions of countries rise progressively.In order to establish this point, I have examined the temperatures of places si-tuated almost on the level of the sea, and under the same parallels.
Whence, in the longitudes of Paris and Buda, and between the latitudes of 47°and 48°, and almost at the level of the sea, the mean temperature is from 50°.9 to51°.44.Under the same longitudes, we have,—
By taking the means of these results, we cannot mistake the influence of smallelevations, or of very extensive plateaus, on the decrease of the mean temperature.* Heated by the winds of Italy.† In spite of the winds of Italy.|276|
In comparing the mean temperature of superincumbent bedsof air, I find that the isothermal line of 41°, which, in the pa-rallel of 45°, is found at the height of 1000 metres, (3280 feet),makes the equatorial mountains of an absolute elevation of 4250metres, (13,940 feet). It had, however, been long believed,after Bouguer, that the inferior limits of perpetual snows cha-racterised every where a bed of air, whose mean temperaturewas 32°; but I have shewn in a Memoir read to the Institutein 1808 *, that this supposition is contrary to experience. Byuniting good observations, I have found, that at the limit of per-petual snows, the mean temperature of the air is,—
As the heat of the higher regions of the atmosphere dependson the radiation of the plains, we may conceive, that, under thesame geographical parallels, we cannot find, in the transatlan-tic climates, (on the declivities of rocky mountains), the isother-mal lines at the same height above the level of the sea as in Eu-ropean climates. The inflexions which these lines experience,when traced on the surface of the globe, necessarily influencetheir position in a vertical plane, whether we unite in the atmo-sphere points placed under the same meridians, or consider onlythose that have the same latitude.
Hitherto we have attempted to determine the mean tempera-tures which correspond under the Equator and in Lat. 45º and
* Observations Astronomiques, tom. i. p. 136.|277| 47° to beds of the atmosphere equally elevated. This determi-nation is founded on stationary observations, and indicates themean state of the atmosphere. General physics has its numeri-cal elements, as well as the system of the world; and these ele-ments, so important in the theory of barometrical measurementsand in that of refractions, will be perfected in proportion as na-tural philosophers shall direct their attention to the study of ge-neral laws.
This Table proves, in conformity with the deductions oftheory, that in the mean state of the atmosphere, the heat doesnot decrease uniformly in an arithmetical progression. In theCordilleras, (and the fact is extremely curious), we observe thedecrease getting less and less between 1000 and 3000 metres,particularly between 1000 and 2500 metres of elevation, andthen increasing anew from 3000 to 4000 metres. The strata,where the decrease attains its maximum and its minimum, arein the ratio of 1 to 2. From the height of the Caraccas to thatof Popayan and Loxa, 1000 metres produce a difference of 6°.3.From Quito to the height of Paramos, the same 1000 metreschange the mean temperature more than 12°.6. Do these phe-nomena depend only on the configuration of the Andes, or arethey the effect of the accumulation of clouds in the aërial ocean?In considering that the Andes form an enormous mass, 3600metres (11,808 feet) high, from which rise peaks or domes in-sulated and covered with snow, we may conceive how, from thepoint where the mass of the chain diminishes so rapidly, theheat decreases also with rapidity. It is not easy, however, to ex-
|278| plain, by an analogous cause, why the progressive cooling dimi-nishes between 1000 and 2000 metres. The great plateaus ofthe Cordilleras commence only at the height of 2600 or 2900metres, (8528 or 9512 feet); and I am of opinion, that the slow-ness with which the heat decreases in the stratum of air between1000 and 2000, is the triple effect of the extinction of light, orthe absorption of the rays in the clouds,—of the formation ofrain,—and the obstacle which the clouds oppose to the freepassage of radiant heat. The bed of air of which we speak, isthe region in which are suspended the large clouds which theinhabitants of the plains see above their heads. The decrease oftemperature, which is very rapid from the plains to the regionof clouds, becomes less rapid in that region; and if this changeis less sensible in the temperate zone, it is no doubt because atthe same height, the effect of radiation there is less sensible thanabove the burning plains of the equinoctial zone. In thesezones, too, the cooling appears to follow the same law in thebeds of air of equal temperature; but the force of radiation va-ries with the temperature of the radiating beds.
The results which we have now discussed, deserve the prefe-rence over those which are deduced from observations made du-ring excursions to the tops of some lofty mountains. The firstgive for the
* This is the mean result or the measure of the distribution of heat in thewhole column of air. The partial results are from the back of the Andes.
In these numbers, we recognise, as in the above Table, the influence of the regionof clouds upon the decrease of heat. In order to shew the utility of these numeri-cal ratios, I shall give here the approximate calculation of the height of the plainof Thibet, deduced from the mean temperature of the month of October, which, ac-cording to the former, is 42°.26. As the latitude of Tissoolumbo 29°, gives 69°.8for the mean temperature of the plain; and as at Mount St Gothard, the mean|279|
The last give for the
This agreement is no doubt very remarkable, and the moreso, as, in comparing stationary with insulated observations, weconfound the mean state of the atmosphere in the course of awhole year with the decrease which corresponds to a particularseason, or a particular hour of the day. M. Gay-Lussac found,in his celebrated aëronautical voyage from 0 to 7000 metres,(0 to 22,960 feet), a centigrade degree for 187 metres, near Pa-ris, at a period when the heat of the plains was nearly equal tothat of the equinoctial region. It is on account of this observedequality in the decrease of heat, in reckoning from the standardtemperature of the plains, that the astronomical refractions cor-responding to angles below 10°, have been found the same un-der the equator and in temperate climates. This result, con-trary to the theory of Bouguer, is confirmed by observationswhich I have made in South America, and by those of Maske-lyne at Barbadoes, calculated by M. Oltmanns.
We have seen, that between the tropics, on the back of theCordilleras, we find, at 2000 metres of elevation, I will not saythe climate, but the mean temperature of Calabria and of Sicily.In our temperate zone, in 46° of Lat. we meet at the same eleva-tion with the mean temperature of Lapland †. This comparison
temperature of October is even a little below that of the whole year, it is probablethat the height of the plain of Great Thibet exceeds from 2900 to 3000 metres.—See my Memoir on the Mountains of India in the Ann. de Chim. et de Phys. 1817. Note by the Editor. As the cold meridian of the globe passes through the plains of Great Thibet,we conceive that the mean temperature of Lat. 29° in that plain, when reduced tothe level of the sea, will be about 65°, and therefore that the height of the plain ofGreat Thibet will not exceed 2800 metres or 9184 feet.—D. B.* Saussure gives for the summer 160 metres, (525 feet); for winter 230, (754feet); and for the whole year 195, (640 feet). M. Ramond gives 165, (538 feet).M. D’Aubuisson 173 metres, (567 feet).—See Journ. de Phys. tom. lxxi. p. 37.; De la Formul. Barometr. p. 189.; and my Recueil d’Obs. Astron. tom. i. p. 129.† As the temperature varies very little in the course of a whole year in theequinoctial zone, we may form a pretty correct idea of the climate of the Cordil-|280| leads us to an exact knowledge of the numerical ratios betweenthe elevations and the latitudes, ratios which we find indicatedwith little precision in works on physical geography. The following are the results which I have obtained from exactdata in the temperate zone, from the plains to 1000 metres of ele-vation. Every hundred metres of perpendicular height, dimi-nishes the mean temperature of the year, by the same quantitythat a change of 1° of latitude does in advancing towards thePole. If we compare only the mean temperature of summer,the first 1000 metres are equivalent to 0°.81 Fahr. From 40°to 50° of latitude, the mean heat of the plains in Europe de-creases in Europe 12°.6 of Fahr.; and this same decrease oftemperature takes place on the declivity of the Swiss Alps from0 to 1000 metres of elevation.
These numerical ratios are deduced from observations madeon the temperature of the air. We cannot measure the quan-tity of heat produced by the solar rays on the parenchyma ofplants, or in the interior of fruits which receive their colour inripening. The fine experiment of MM. Gay-Lussac and The-nard, the combustion of chlorine and hydrogen, proves what apowerful action direct light exercises on the molecules of bodies.But as the extinction of light is less upon the mountains in dryand rarified air, maize, fruit-trees, and the vine, still flourish atheights which, according to our thermometrical observationsmade in the air, and far from the ground, we ought to suppose
leras, by comparing them to the temperature of certain months in France or inItaly. We find in the plains of Orinoco the month of August of Rome; at Po-payan, (2988 feet), the month of August of Paris; at Quito (4894 feet), the monthof May; in the Paramos, (5904 feet), the month of March at Paris.|281| too cold for the cultivation of plants useful to man. M. DeCandolle, indeed, to whom the geography of vegetables owes somany valuable observations, has seen the vine cultivated in thesouth of France at 800 metres (2624 feet) of absolute height,when, under the same meridian, this same cultivation went onwith difficulty at 4º of latitude farther north; so that if we con-sider only the ratios in France, an elevation of 100 metres, (328feet), appears to correspond, not to 1°, but to half a degree of la-titude *. (To be concluded in next Number.)
* See my Prolegomena de Distributione Plantarum, p. 151.—163. The smalldifferences between the numbers given in the Prolegomena and in this Memoir,written subsequently, should be ascribed to the constant desire which I have hadto perfect the mean results.|28|
I SHALL now conclude this Memoir by the enumeratıon ofthe most important results which have been obtained by BaronVon Buch, M. Wahlenberg, and myself, on the distribution ofheat in the interior of the earth, from the Equator to 70° of N.Lat., and from the plains to 3600 metres (11,808 feet) of ele-vation. I shall limit myself to an enumeration of the facts.The theory by which these facts are connected, will be found inthe fine analytical work with which M. Fourier will soon enrichnatural philosophy.
The interior temperature of the earth is measured either bythe temperature of subterraneous excavations, or by that ofsprings. This kind of observation is very liable to error, if thetraveller does not pay the most minute attention to local circum-stances, which are capable of altering the results *. The air,when cooled, accumulates in caverns, which communicate withthe atmosphere by perpendicular openings. The humidity ofrocks depresses the temperature by the effect of evaporation.Caverns that have little depth are more or less warmed, accor-ding to the colour, the density, and the moisture, of the strataof stone in which nature has hollowed them. Springs indicatetoo low a temperature, if they descend rapidly from a consider-able height upon inclined strata. There are some under thetorrid zone and in our climate, which do not vary in their tem-perature throughout the whole year more than half a degree;and there are others which shew the mean temperature of theearth only by observing them every month, and taking the meanof all the observations. From the Polar circle to the Equator,and from the tops of mountains towards the plains, the progres-sive increase of the temperature of springs diminishes with the
* Baron von Buch, in the Bibl. Brit. tom. xix. p. 263.; Saussure, Voyages, sect. 1418.; Wahlenberg, De Veget. Helvet. Pl. 77.—84.; Gilbert, Annalen, 1812,p. 150. 160. 277.; Lambert, Pyrometrie, p. 296. Dr Roebuck appears to havebeen the first who entertained exact notions on the temperature of springs, andupon their relation to the mean temperature of the air; Phil. Trans. 1775, vol. lxv.p. 461.|29| mean temperature of the ambient air. The temperature of theinterior of the earth is, at
In equinoctial America, I have found it in the plains from77° to 78°.8.
The following are examples of the decrease of temperaturefrom the plains to the tops of mountains.
Between the Tropics I have found,
In the plains, and to the height of 3280 feet, between the pa-rallels of from 40° to 45°, the mean temperature of the earth isnearly equal to that of the ambient air; but very accurate ob-servations by Baron Von Buch and Wahlenberg tend to prove,that in high latitudes, towards the top of the Swiss Alps, forexample, beyond the height of 1400 or 1500 metres (4592 or4920 feet), the springs and the earth are 5°.4 warmer than theair.
|30|
At Enontekies, in 68\( \frac{1}{2} \)° of Lat. the difference between themean temperatures of the earth and the air, is so great as 7°.74.Analogous differences are observed on the back of the Alps, atthe altitude of 1400 metres (4592 feet).
In the following small table, I have added the mean tempe-rature of the atmosphere, by supposing, with M. Ramond,that there is a decrease of 1° centigrade for 164 metres (1° Fahr.for 300 feet nearly), and by placing the temperature of 32° (ac-cording to observations made at the Hospice of St Gothard), at1950 metres (6396 feet) of elevation.
It may be objected, that in the Alps of Switzerland, the tem-perature of springs has only been observed from the beginningof June to the end of September, and that the differences be-tween the air and the interior of the earth would almost entire-ly disappear, if we knew the temperature of the springs duringthe whole year. It must not be forgotten, however, that thesprings of the Alps did not vary in the space of four months atthe time of the observations of M. Wahlenberg;—that amongthe small number of scanty springs which indicate changes oftemperature in different seasons, these variations amount fromJune to September to 11° or 15°;—and that several springs,particularly those which are very copious, do not vary duringa whole year more than half a degree of Fahrenheit.
It appears to me, therefore, sufficiently certain, that wherethe earth is covered with a thick stratum of snow, while thetemperature of the air descends to 15° or — 4° of Fahrenheit,the temperature of the earth is above the mean temperature ofthe air.
When we consider what a large portion of the globe is cover-ed with the sea, and examine the temperature of the deepestwaters *, we are constrained to admit, that in islands, along
* At Funchal in Madeira, the temperature of caverns appears to be 61°.16, andconsequently 7°.2 below that of the air.—Phil. Trans. 1778, p. 372.|31| coasts, and perhaps even in continents of small extent, the inte-rior heat of the earth is modified by the proximity of the strataof rocks on which the waters of the ocean rest. I have considered successively in this memoir, the distributionof heat,
In the following general Table of the distribution of heat,the temperatures are expressed in degrees of Fahrenheit; thelongitudes are reckoned from east to west of the meridianof the observatory of Greenwich. The mean temperatures ofthe seasons have been calculated, so that those of the months of December, January, and February, form the mean temperatureof Winter. An asterisk (*) is prefixed to those places whosemean temperatures have been most accurately determined, andin general by means of 8000 observations. The isothermallines have a convex summit in Europe, and two concave sum-mits in Asia and Eastern America |32|
|34|
1 Coast of Labrador. Two years of observations. Floatingice towards the east. A transatlantic climate. Mean temp. ofOct. about 32°.72; Nov. 26°.68.
2 Centre of Lapland. A European climate. Fine vegetation.June, 49°.46; July, 59°.54; Aug. 55°.94; Sept. 41°.74; Oct. 27°5;Nov. 12°.38. Inland situation. Specimen of a continental cli-mate.
3 Eleven years of observations, calculated afresh in decads byWahlenberg. Thermometer verified by Saussure. Mean temp.of seven months of the year below 32°. Winds blow from Italyin the winter. Minimum observed in the winter— 0°.4; inAug. at noon, in the shade, maximum 54°.5; the nights in Aug.frequently from 33°.8 to 29°.3; the mean temp. of Oct. 31°.1 re-presents that of the whole year; at the Col de Géant, 10,598 feethigh, the mean temp. of July is 36°.5. We find 32° to be themean temp. in Europe in 45° of latitude, at 5,400 feet high;at the parallel of the Canaries, at 12,300 feet; in the Andes, un-der the Equator, at 16,500 feet.
4 Buch, Voy. en Norw. ii. 416. Specimen of the climate ofthe islands and coasts in the north of Europe. April, 30°.02;May, 33°.98; Oct. 32°; Nov. 25°.88. At Alten, Lat. 70°, meantemp. of July, 63°.5; a continental climate.
5 Finland, eastern coast. May, 40°.82; June, 55°.04; July,61°.52; Aug. 56°.66; Sept. 46°.58; Oct. 38°.66; Nov. 24°.62.Julin and Buch.
6 Eastern coast of Western Bothnia. Dr Nœzen. March,23°.18; April, 33°.98; Oct. 38°.12; Nov. 24°.62.
7 Euler. Mean temp. of the year, 37°.94. Inochodzow.
Acta. Petr. xii. 519,—533.
8 Two years. Berlin, in the Mem. de l’Acad. de Drontheim,
iv. 216. April, 34°.34; May, 50°.74; Oct. 39°.2; Nov. 27°.68.Climate of the west coast of Europe.
9 Four years. Journal de Phys. xxxix. 40. A continentalclimate. Winter colder, and summer warmer than at Peters-burg. Eastern part of Europe; height as taken from Stritter.(Chamouni, Lat. 46° 1′; Long. 6° 18′ E.; height, 3,168 feet;mean temp. 39°.2.)
10
Twelve years. Kirwan. Cotte, mean of the year, 41°.18;of the summer, 67°.46; too high. West coast of Finland.
|35|
11
Observations from 1774 to 1804, made by Mallet, Pros-perin, Holmquist, and Schleling, calculated by M. De Buch, Voy.de Norw. ii. 309. It is, perhaps, the place the mean temp ofwhich is the best determined. Winters more serene than atStockholm; colder on account of the radiation of the groundand the air.
12
Thirty-nine years of observations, 15 of which are verygood. Wargentin. Cotte, mean temp. of the year, 44°.24.Five months below 32° as at Petersburg.
13
Four years. A transatlantic climate.
14
Buch, two years. Mean temp. of the winter often scarce-ly 31°.1. West coast.
15
Alps of Bavaria. Six years’ observations, calculated byM. Wahlenberg. Many fruit trees. Convent of Tegernsée, inBavaria, height of, 2,292 feet; mean temp. of 1785, 42°.44;Peyssenberg, 41°.
16
Bugge. Three months below 32°. Under the Equator,mean temp. of 44°.6, at an elevation of 18,000 feet.
17
Dalton. West of England. Climate of islands; springs47°.84. Keswick, Lat. 54° 33′, Long. 3° 3′ W.; mean temp.48°.02; springs, 48°.56.
18
Kirwan. Scarcely two years’ observations. Southernlatitude.
19
Strnadt. Fifteen years. Climate of the continent of Eu-rope.
20
Mayer.
21
Six years’ observations of M. Escher, calculated by Wah-lenberg. The town is situated in a hollow, to which those warmwinds cannot penetrate, that render the winters more temperatein the other parts of Switzerland.
22
The calculation has been made from six years of excellentobservations, by Professor Playfair; during this time the ther-mometer was never seen above 75°.74 *. Vegetation continuesfrom March 20. to Oct. 20.; mean temp. of these seven monthsis from 55°.76 to 50°.90, according as the years are more or lessfruitful; wheat does not ripen if the mean temp. descends to47°.66.
* See Edinburgh Transactions, vol. ix. p. 209.—Ed. |36| 23 Guittard. Only three years. Mean temp. a little toohigh. Eastern part of Europe. A continental climate. 24 Four years of observations, by M. de Salis Sewis, calcu-lated by M. Wahlenberg. Mountains of the Grisons. 25 Kirwan. Irish Trans. viii. 203. and 269. Specimen ofthe climate of the islands. Coldest days, 23°; interior of theground, 49°.28. Hamilton. 26 The climate of Berne is a continental climate, in compari-son with that of Geneva; there is no lake near it. 27 Seven years of observations. Saussure. Mean temp. 50°74. Voy. § 1418. I find the mean temp. from 1796—1815, 49°.7.Interior of the earth, 51°.98. Pictet, Bibliotheque Brit. 1817,iv. 109. 28 Six years. 29 Austria. Berlin, Lat. 52° 31′; mean temp. probably 46°.4to 47°.3; according to Beguelin, 48°.74; springs, 49°.28. Ra-tisbon, Lat. 49°; height, 1,104 feet; mean temp. 47°.66. Mu-nich, Lat. 48° 8′; height, 1,608 feet; mean temp. 50°.74. 30 Ramond. Seven years of excellent observations. Themean of the months, at noon, well ascertained; winter, 39°.92;spring, 57°.02; summer, 70°.88; autumn, 57°.92. Mem. Inst. 1812, p. 49. Cotte, mean temp. 51°.26. 31 Wahlenberg, Flor. Carp. p. 90. Continental climate.Height of the observatory, 474 feet. 32 Two years, near Boston, in New England. Transatlanticclimate. The thermometer sometimes descends to 0°. 33 Eleven years (1803—1813) of observations made at theobservatory. A greater number of years will, perhaps, give themean temp. a little higher. Vaults, 53°.06. Kirwan finds forParis, from seven years of observations of unequal value, 51°.62;he fixes upon 52°.7. Cotte, from 29 years of observations, (Journ. de Phys. 1782, July), 53°.24. Cotte, for 33 years,(1763—1781, Mem. Instit. iv. 266.), 52°.34. The extraordinaryyear of 1816 offers the mean temp. of 48°.74; winter, 37°.04;spring, 48°.92; summer, 59°.54; autumn, 50°: the precedingyear, 1815, offers a mean temp. of 50°.74; winter, 37°.04; spring,52°.7; summer, 62°.78; autumn, 50°.74. Arago. Mean temp.of Montmorency, for 33 years, 50°.74; height, 498 feet. Cotte, |37| Strasburg, Lat. 48° 34′; height, 480 feet; mean temp. 49°.28.Herrenschneider. 34 Dr Young. Mean temp. varies from 47°.84 to 51°.62, (Lectures, ii. 453.) Cavendish, (Trans. 1788, p. 61.), 48°.74,Roebuck, Hunter, and Kirwan, 51°.62. Horsley, 51°.26. Ac-cording to Kirwan, the four seasons in London are, 39°.56, 50°.9,64°.76, 51°.98; at Paris, 36°.68, 51°.08, 65°.84, 52°.52; fromwhıch results, London, 51°.62; Paris, 51°.44. Cotte (Journ. dePhys. xxxix. 36.) thinks London is 51°.26, and Paris, 52°.34.The difference which we observe in cultivated plants dependsless upon mean temp. than upon direct light, and the serenityof the atmosphere. 35 Seven years. Cotte. Lisle, 48°.38; Rouen, 51°.44;Cambray, 51°.98; Soissons, 53°.42; Rethel, 53°.24; Metz, 52°.88;Nancy, 51°.98; Etampes, 51°.08; L’Aigle, 50°.9; Brest, 54°.14;Mayenne, 51°.98. 36 Mohr, and Van Swinden. Five years. 37 Thirteen years. Temperature rather too high? 38 Eleven years. Van Swinden. From 1771—1783. Meantemp. 51°.26. 39 Concave transatlantic summit. Seven years of observa-tions give 54°.86; for the four seasons, 33°.98, 53°.06, 75°.2,56°.12. Rush, 52°.52, (Drake’s View of Cincin. p. 116.) Coxe,54°.14. M. Legaux finds for 17 years, for Springmill on theSchuylkill, Lat. 40° 50′; mean temp. 53°.42. Springs, nearPhiladelphia, 54°.86, Warden. 40 Two years only. Retif de la Serve. The thermometersometimes descends to — 4° in the parallel of Naples! Springs,54°.86. Ipswich, Lat. 42° 38′; mean temp. 50°. Williamsburg,in Virginia, 58°.1. Cotte and Kirwan. Transatlantic climates. 41 Transatlantic climates west of the Alleghanys. Good ob-servations, from 1806—1813. Col. Mansfield, (Drake, p. 93.) Minimum of the winter, from 5° to — 9°.4; Jan. 1797, as lowas — 16°.6, for 39° latitude. Maximum 89°.6 to 107°.6 in theshade, without reflection; \( \frac{1}{3} \) of all the winds SW.; springs nearCincinnati, 54°.32. Little snow falls; but it is abundant betweenLat. 40° and 42°. 42 Three years only. Bougourd. Dijon, height, 810 feet; |38| Lat. 47° 19′; mean temp. 50°.9. Besançon, height, 804 feet;Lat. 47° 14′; mean temp. 51°.26. 43 Six years. Duplessis, and Boudan. Temperature of thesummer too high? Rochelle, 53°.06; Poitiers, 52°.7. 44 Amyot. Six years. Concave. Asiatic summit. Threemonths below 32°, as at Copenhagen; the summer like that atNaples. 45 One of the best determined points. The years 1789—1812are calculated in decads of days. Observations of the Astrono-mer Reggio, April, 55°.76; Oct. 58°.1. The two decads whichapproach the nearest to the mean temp. of the year, are, the firstof April, 53°.24; and the last of Oct. 54°.68. The mean temps.for January have varied in 10 years from 24°.98 to 38°.48;those of July, from 71°.42 to 78°.44; the mean of the years,from 54°.5 to 57°.2. (Reggio, taking only 24 maxima and mi-nima in a year for 1763—1798; mean temp. 55.4, Ephem. Mil. 1779, p. 82.) 46 Ten years. Guyot. Lyons, 528 feet, 55°.76. Mafra,near Lisbon, Lat. 38° 52′; height, 600 feet; mean temp. 56°.3,too small. Mem. de Lisbonne, ii. 105—158. 47 Seven years, (1777—1782). St Jacques de Sylvabelle.The thermometer sometimes descends to 23°. Cotte, Traité deMet. ii. 420.) 34 years (Raymond, in Mem. de la Soc. de Med. 1777, p. 86.) give 62°.06. Cotte (Journ. de Phys. xxxix. 21.)fixes it at 58°.64. Kirwan, at 61°.24. The observations madeat the Royal Observatory of Marseilles can alone decide. 48 Ten years. Nismes, 60°.26; Perpignan, 59°.54; Taras-con, 59°.9; Arles, 59°; Rieux, 57°.2: Montauban, 55°.58; To-nains, 54°.86; Dax, 54°.14; Rodez, 57°.02; Aix, 56°.66. Un-der the equator, 57°.74, at 9,000 feet of elevation. 49 William Humboldt. Calandrelli, 60°.08. The thermo-meter sometimes descends to 24°.5, and rises to 99°.5. Naples,67°.1; Toaldo, probably 63°.5; Florence, 61°.52; Tartini, toohigh; Lucca, 60°.44; Genoa, 60°.26; Bologna, 56°.3; Verona,55°.76; Venice, 56°.48; Padua, 56°.3. Kirwan regards it as anestablished fact, that in Europe the mean temp. in Lat. 40°, is61°.88; in Lat. 50°, 52°.52. 50 Only two years. Barberet, and d’Angos. Sheltered bymountains. Estimate a little too high. |39| 51 Japan. A single year. Voy. de Thunberg, p. 121. Cli-mate of islands. Under the Equator, 64°.4, at a height of 6000feet. 52 West of the Alleghanys, in Louisiana. Four years. Dun-bar. Transatlantic climate. 53 Madeira. Heberden. Climate of islands. St Croix, ofTeneriffe, 71°.42. The remainder of the island of Teneriffe, inthe plains, 69°.26. Buch. 54 Old observations of Tartebout. They appear good. Bag-dad, Lat. 33° 19′; according to Beauchamps, 73°.76. The fourseasons, 50°.74; 74°.64; 92°.66; 77°; but there was reflectionfrom a house. The thermometer falls to 29°.44. Under theEquator, at 3,000 feet high; mean temp. 71°.24. 55 The calculations are made from the observations of Nouet, (Decade, ii. 213.) The following are the mean temps. of the12 months: 58°.1; 56°.12; 64°.58; 77°.9; 78°.26; 83°.66;85°.02; 85°.82; 79°.16; 72°.32; 62°.96; 61°.24. (Niebuhr,72°.2.) Temp. of Joseph’s Well, 72°.5. Catacombs of Thebes,81°.5. Well of the great pyramid, surrounded by sand, 88°.16.Jomard. Bassora, on the Persian Gulf; mean temp. 77°.9;winter, 64°.04; summer, 90°.86; July, 93°.2. 56 Orta. Humboldt, Nouv. Esp. iv. 516. Jamaica, coast,80°.6. Blagden. 57 Ferrer, 1810—1812. Con. des Tems, 1817, p. 338.Wells of 10 feet deep; air, 75°.92; water, 74°.48; in 1812, maximum, Aug. 14. 86°; minimum, Feb. 20. 61°.52. Grot-tos, 81°.5. Humboldt, Observ. Astron. i. 134. 58 Humboldt. Pondicherry, 85°.1; Madras, 80°.42; Ma-nilla, 78°.08; Isle de France, coast, 80°.42.
On Isothermal Lines, and the Distribution of Heatover the Globe. By Baron Alexander de Humboldt *.
* As this interesting and valuable Memoir, the original of which was publishedin the Memoires D’Arcueil, tom. iii. p. 462, has never appeared in our language,and as it must be constantly referred to in all subsequent speculations on Meteoro-logy, and should be familiar to every person who pursues this important study, wehave resolved to present a translation of it to our readers. A small part of thememoir appeared in an English journal; but almost all the reductions from theCentigrade to Fahrenheit’s scale were so erroneous, that the numbers cannot betrusted. We have added various notes, which will be distinguished from those ofthe Author by affixing Ed. to the former, and H to the latter.—Ed. |2| will be of considerable importance to fix the numerical relationby which a great number of scattered observations are connect-ed, and to reduce to empirical laws the effects of local and dis-turbing causes. The study of these laws will point out to tra-vellers the problems to which they should direct their principalattention, and we may entertain the hope, that the theory of thedistribution of heat will gain in extent and precision, in propor-tion as observations shall be more multiplied, and directed tothose points which it is of most importance to illustrate. As the phenomena of geography and of vegetables, and ingeneral the distribution of organised beings, depend on theknowledge of the three co-ordinates of Latitude, Longitude, andAltitude, I have been occupied for many years in the exactvaluation of atmospherical temperatures; but I could not re-duce my own observations without a constant reference to theworks of Cotte and Kirwan, the only ones which contain a greatmass of meteorological observations obtained by instrumentsand methods of very unequal precision. Having inhabited fora long time the most elevated plains of the New Continent, Iavailed myself of the advantages which they present for exa-mining the temperature of the superincumbent strata of air,not from insulated data, the results of a few excursions tothe crater of a volcano, but from the collection of a greatnumber of observations made day after day and month aftermonth in inhabited districts. In Europe, and in all the OldWorld, the highest points of which the mean temperatureshave been determined, are the Convent of Peissenberg in Bavaria,and the Hospice of St Gothard *. The first of these is placedat 3264, and the second at 6808 feet above the level of the sea.In America a great number of good observations have beenmade at Santa Fe de Bogota and at Quito, at altitudes of8,727 and 9,544 feet. The town of Huancavelica, containing10,000 inhabitants, and possessing all the resources of moderncivilisation, is situated in the Cordilleras of the southern hemi-
* The mean temperature of the air at the Convent of the Great St Bernard, theheight of which is 7,960 feet, is not determined. There are several villages inEurope placed at more than 5000 feet of altitude; for example, St Jacques deAyas at 5,479, and Trinita Nuova, near Grasfoncy, at 5,315 feet.—H.|3| sphere at 12,310 feet of absolute elevation; and the mine ofSanta Barbara, encircled with fine edifices, and placed a leagueto the south of Huancavelica, is a place fit for making regularobservations, at the height of 14,509 feet, which is double thatof the Hospice of St Gothard. These examples are sufficient to prove how much our know-ledge of the higher regions of the atmosphere, and of the phy-sical condition of the world in general, will increase, when thecultivation of the sciences, so long confined to the temperatezone, shall extend beyond the tropics into those vast regions,where the Spanish Americans have already devoted themselveswith such zeal to the study of physics and astronomy. In or-der to compare with the mean heat of temperate climates, theresults which M. Bonpland and I obtained in the equinoctialregions from the plains to the height of 19,292 feet, it was ne-cessary to collect a great number of good observations made be-yond the parallels of 30° and 35°. I soon perceived how vaguesuch a comparison was, if I selected places under the meridianof the Cordilleras, or with a more eastern longitude, and I there-fore undertook to examine the results contained in the mostrecent works. I endeavoured to find, at every 10° of latitude,but under different meridians, a small number of places whosemean temperature had been precisely ascertained, and throughthese, as so many fixed points, passed my isothermal lines or linesof equal heat. I had recourse, in so far as the materials have beenmade public, to those observations the results of which have beenpublished, and I found, in the course of this easy, but longand monotonous labour, that there are many mean temperaturespointed out in meteorological tables, which, like astronomicalpositions, have been adopted without examination. Sometimesthe results were in direct contradiction to the most recent obser-vations, and sometimes it was impossible to discover fromwhence they were taken. Many good observations were rejected, solely because theabsolute height of the place where they were made was un-known. This is the case with Asia Minor, Armenia and Per-sia, and of almost all Asia; and while the equinoctial part aloneof the New World presents already more than 500 points, thegreater number of which are simple villages and hamlets, de- |4| termined by barometrical levelling, we are still ignorant of theheight of Erzeroum, Bagdad, Aleppo, Teheran, Ispahan,Delhi and Lassa, above the level of the neighbouring seas.Notwithstanding the intimate relation in which we have latelystood with Persia and Candahar, this branch of knowledge hasnot made any progress in the last fifty years. We are not authorised, however, on account of the decreaseof temperature in the upper regions of the atmosphere, to con-found the mean temperatures of places which are not placed onthe same level. In the Old World, good observations, which canalone be used for establishing empirical laws, are confined to anextent between the parallels of 30 and 70 degrees of latitude,and the meridians of 30° east longitude, and 20° of west longi-tude. The extreme points of this region are the island of Ma-deira, Cairo, and the North Cape. It is a zone which is only athousand nautical leagues, (1|7th of the circumference of theglobe,) from east to west, and which, containing the Basin of theMediterranean, is the centre of the primitive civilisation ofEurope. The extraordinary shape of this part of the world,the interior seas and other circumstances, so necessary for de-veloping the germ of cultivation among nations, have given toEurope a particular climate, very different from that of otherregions placed under the same latitude. But as the physicalsciences almost always bear the impress of the places where theybegan to be cultivated, we are accustomed to consider the distri-bution of heat observed in such a region, as the type of the lawswhich govern the whole globe. It is thus that, in geology, wehave for a long time attempted to refer all volcanic phenomenato those of the volcanoes in Italy. In place of estimating me-thodically the distribution of heat, such as it exists on the sur-face of continents and seas, it has been usual to consider asreal exceptions every thing which differs from the adopted type,or, by pursuing a method still more dangerous in investigatingthe laws of nature, to take the mean temperatures for every fivedegrees of latitude, confounding together places under differentmeridians. As this last method appears to exclude the influ-ence of extraneous causes, I shall first discuss it briefly before Iproceed to point out the method, essentially different, which Ihave followed in my researches. |5| The temperature of the atmosphere, and the magnetism ofthe globe, cannot, like those phenomena which depend on onecause, or on a single centre of action, be disengaged from theinfluence of disturbing circumstances, by taking the averages ofmany observations in which these extraneous effects are mutuallydestroyed. The distribution of heat, as well as the dip and va-riation of the needle, and the intensity of the terrestrial mag-netism, depend, by their nature, on local causes, on the consti-tution of the soil, and on the particular disposition of the radiat-ing surface of the globe. We must, however, guard againstconfounding under the name of extraneous and disturbing causes,those on which the most important phenomena, such as the dis-tribution and the more or less rapid developement of organiclife, essentially depend. Of what use would it be to have a tableof magnetic dips, which, in place of being measured in parallelsto the magnetic equator, should be the mean of observationsmade on the same degrees of terrestrial latitude, but under dif-ferent meridians? Our object is to ascertain the quantity ofheat which every point of the globe annually receives, and, whatis of most importance to agriculture, and the good of its inha-bitants, the distribution of this quantity of heat over the diffe-rent parts of the year, and not that which is due to the solaraction alone, to its altitude above the horizon, or to the dura-tion of its influence, as measured by the semidiurnal arcs. Moreover, we shall prove, that the method of means is unfitfor ascertaining what belongs exclusively to the sun, (inasmuchas its rays illuminate only one point of the globe,) and what isdue both to the sun and to the influence of foreign causes.Among these causes may be enumerated the mixture of the tem-peratures of different latitudes produced by winds;—the vicini-ty of seas, which are immense reservoirs of an almost invariabletemperature;—the shape, the chemical nature, the colour, theradiating power and evaporation of the soil;—the direction ofthe chains of mountains, which act either in favouring the playof descending currents, or in affording shelter against particularwinds;—the form of lands, their mass and their prolonga-tion towards the poles;—the quantity of snow which covers themin winter, their temperature and their reflection in summer;—and, finally, the fields of ice, which form, as it were, circumpolar |6| continents, variable in their extent, and whose detached partsdragged away by currents modify in a sensible manner the cli-mate of the temperate zone. In distinguishing, as has long been done, between the solar and the real climate, we must not forget, that the local and mul-tiplied causes which modify the action of the sun upon a singlepoint of the globe, are themselves but secondary causes, the ef-fects of the motion which the sun produces in the atmosphere,and which are propagated to great distances. If we considerseparately (and it will be useful to do this in a discussion pure-ly theoretical) the heat produced by the sun, the earth beingsupposed at rest and without an atmosphere, and the heat dueto other causes regarded as disturbing ones, we shall find thatthis latter part of the total effect is not entirely foreign to thesun. The influence of small causes will scarcely disappear bytaking the mean result of a great number of observations; forthis influence is not limited to a single region. By the mobilityof the aerial ocean, it is propagated from one continent to ano-ther. Every where in the regions near the polar circles, the ri-gours of the winters are diminished by the admixture of the co-lumns of warm air, which, rising above the torrid zone, arecarried towards the poles: Every where in the temperate zone,the frequent west winds modify the climate, by transportingthe temperature of one latitude to another *. When we re-flect, besides, on the extent of seas, on the form and prolonga-tion of continents, either in the two hemispheres, or to the eastand west of the meridians of Canton and of California, we shallperceive, that even if the number of observations on the meantemperature were infinite, the compensation would not take place. It is, then, from the theory alone that we must expect to deter-mine the distribution of heat over the globe, in so far as it dependson the immediate and instantaneous action of the sun. It doesnot indicate the degrees of temperature expressed by the dilata-tion of the mercury in a thermometer, but the ratios between themean annual heat at the equator, at the parallel of 45°, and un-der the polar circle; and it determines the ratios between thesolstitial and equinoctial heats in different zones. By comparing
* Raymond, Memoire sur la Formule Baromet. p. 108 and 113.|7| the results of calculation, not with the mean temperature drawnfrom observations made under different longitudes, but withthat of a single point of the earth’s surface, we shall set out withthat which is due to the immediate action of the sun, and to thewhole of the other influences, whether they are solar or local, orpropagated to great distances. This comparison of theory withexperience will present a great number of interesting relations. In the year 1693, previous to the use of comparable thermo-meters, and to precise ideas of the mean temperature of a place,Halley laid the first foundations of a theory of the heating ac-tion of the sun under different latitudes *. He proved that theseactions might compensate for the effect of the obliquity of therays. The ratios which he points out, do not express the meanheat of the seasons, but the heat of a summer day at the equa-tor and under the polar circle, which he finds to be as 1.834 to2.310 †. According to Geminus ‡, Polybius among the Greekshad perceived the cause why there should be less heat at theequator than under the tropic. The idea also of a temperatezone, habitable and highly elevated in the midst of the torridzone, was admitted by Eratosthenes, Polybius, and Strabo. In two memoirs §, published at long intervals in 1719 and1765, Mairan attempted to solve the problems of the solar action,by treating them in a much more extended and general manner.He compared, for the first time, the results of theory with thoseof observation; and as he found the difference between theheat of summer and winter much less than it ought to be bycalculation, he recognised the permanent heat of the globe andthe effects of radiation. Without mistrusting the observations he employed, he con-ceived the strange theory of central emanations which increasethe heat of the atmosphere from the equator to the pole. Hesupposes that these emanations decrease to the parallel of 74°,where the solar summers attain their maximum, and that theythen increase from 74° to the pole. Lambert ¶, with that
* Phil. Trans. 1693, p. 878.† This should be 2.339.—Ed. ‡ Isag. in Aratum, cap. 13.; Strabo, Geogr. lib. ii. p. 97.§ Mem. de l’Acad. 1719, p. 133; and 1765, p. 145. and 210.¶ Pyrometrie oder Vom Maase des Feuers, 1779, p. 342.|8| sagacity which distinguishes all his mathematical researches, haspointed out in his Pyrometrie the error of Mairan’s theory.He might have added, that this geometer confounds a quantityof heat which a point of the globe receives under the latitude of60° during the three months of summer, with the maximum towhich the inhabitants of these northern regions see theirthermometers rising in a clear day. The mean tempera-tures of the summers, far from decreasing from the pole to thetropics, are under the equator, under the parallel of 45°, andunder that of Stockholm, Upsal, or St Petersburg, in the ratioof 81°.86; 69°.8; 61°.16 of Fahrenheit’s scale. Reaumur hadsent his new thermometers to the torrid zone, to Syria, and to thenorth. As it was then reckoned sufficient to mark the warmestdays, an idea was formed of an universal summer, which is thesame in all parts of the globe. It had been remarked, and withreason, that the extreme heats are more frequent, and even morepowerful, in the temperate zone in high latitudes, than underthe torrid zone. Without attending to the mean temperatureof months, it was vaguely supposed, that in these northern re-gions the summers followed the ratio of the thermometrical ex-tremes. This prejudice is still propagated in our own day,though it is well established, that in spite of the length of thedays in the north, the mean temperatures of the warmest monthsat Petersburg, Paris, and the Equator, are 65°.66; 69°.44, and82°.4. At Cairo, according to the observations of Nouet, thethree months of summer are 84°.74, and consequently 19°warmer than at St Petersburg, and 15° warmer than at Paris.The summer heats of Cairo, are almost equal to those I haveexperienced at Cumana and La Guayra between the tropics. With regard to the central emanation of the system of Mai-ran, or to the quantity of heat which the earth gives to the am-bient air, it is easy to conceive that it cannot act in all seasons.The temperature of the globe at the depths to which we canreach, in general differs little from the mean annual temperatureof the atmosphere. Its action is of great importance for the pre-servation of vegetables; but it does not become sensible in theair, unless where the surface of the globe is not entirely coveredwith snow, and during those months, whose mean temperature |9| is below that of the whole year. In the south of France, forexample, the radiation of the earth may act upon the atmos-phere in the five months which precede the month of April. Wespeak here of the proper heat of the globe, of that which is in-variable at great depths, and not of the radiation of the surfaceof the globe, which takes place even at the summer solstice, andthe nocturnal effects of which have furnished M. Prevost withan approximate measure of the direct action of the sun *. Mairan had found, that in the temperate zone the heat of thesolar summer is to that of the solar winter as 16 to 1. M. Pre-vost admits for Geneva 7 to 1. Good observations have givenme for the mean temperature of the summers and the winters atGeneva 34°.7; 64°.94; and at St Petersburg 46°.94 and 62°.06.These numbers neither express ratios nor absolute quantities,but thermometrical differences considered as the total effect ofthe calorific influences; the ratios furnished by theory separatethe solar heat from every other indirect effect. Euler was notmore successful than Mairan in his theoretical essays on the so-lar heat. He supposes that the negative sines of the sun’s alti-tude during the night give the measure of the nocturnal cool-ing, and he obtains the extraordinary result †, that under theequator the cold at midnight ought to be more rigorous thanduring winter, under the poles. Fortunately, this great geo-meter attached but little importance to this result, and to the the-ory from which it is deduced. The second memoir of Mairan,without adding to the problems which had been attempted sincethe time of Halley, has at least the advantage of containing somegeneral views on the real distribution of heat in different conti-nents. It is true, that the extreme temperatures are there con-stantly confounded with the mean temperatures; but previousto the works of Cotte and Kirwan, it was the first attempt togroup the facts, and to compare the most distant climates. Dissatisfied with the route followed by his predecessors, Lam-bert, in his Treatise on Pyrometry, directed his attention to twovery different objects. He investigated analytical expressionsfor the curves, which express the variation of temperature in a
* Du Calorique rayonnant, p. 271. 277. 292.† Comment. Petrop. tom. ii. p. 98.|10| place where it had been observed, and he resumed in its great-est generality the theorem of solar action. He gives formulæ,from which we may find the heat of any day at all latitudes;but being perplexed with the determination of the nocturnal dis-persion of the acquired heat, or the subtangents of the noctur-nal cooling *, he gives tables of the distribution of heat underdifferent parallels, and in different seasons †, which deviate somuch from observation, that it would be very difficult to ascribethese deviations to the heat radiating from the globe, and to dis-turbing causes. We are struck with the slight difference whichthe theory indicates between the mean annual temperatures ofplaces situated under the equator and the polar circle, and be-tween the summers of the torrid zone and those of the tempe-rate zone. It cannot be expected, indeed, that analysis is ca-pable of determining the distribution of heat such as it existson the surface of the globe. Without employing empiricallaws, and deducing the data from actual observation, the theo-ry can subject to calculation only a part of the total effect,or that which belongs to the immediate action of the solar rays;but after the recent successful applications of analysis to thephenomena of the radiation of surfaces, the transmission of heatthrough solid bodies, and the cooling of these bodies in mediaof variable density, we may still expect to be able to perfectthe theory of solar action, and to compute the distribution ofthe heat received into the exterior crust of our planet. In discussing what may be expected from the purely theoreticallabours of Geometers, I have not spoken of a celebrated, butvery concise Memoir of Mayer, the reformer of the LunarTables. This work, written in 1755, was published twentyyears afterwards, in his Opera Inedita ‡. It is a method, and
* Pyrometrie, p. 141, 179.† Id. 318, 339.‡ De Variationibus Thermometri accuratius definiendis, (Opera inedita, vol. i.p. 3—10.) M. Daubuisson, in a note inserted in the Journal de Physique, tom. lxii.p. 449. has given a formula which accords better with observation than thatof Mayer. He admits that the temperature increases from the pole to the equa-tor, as the cosine of the latitude raised to the power of 2\( \left (\frac{1}{2} \right) \)°; but he judicious-ly adds, that this formula is applicable only to a zone of the Old World, nearthe Northern Atlantic Ocean—H.|11| not a theory: It is an essay essentially different from those wehave quoted, and, as its learned author calls it, a determinationof the mean heat found empirically by the application of co-efficients furnished by observation. The method of Mayer isanalogous to that which Astronomers pursue with so much suc-cess, when they correct by small steps the mean place of a planet,by means of the inequalities of its motion: It does not presentthe result of the solar action disengaged from the influence of fo-reign circumstances; but, on the contrary, it estimates the tem-peratures such as they are distributed over the globe, whateverbe the cause of that distribution. The mean heat of two placessituated under different latitudes being given, we find by a simpleequation the temperature of every other parallel *. The calcula-tions of Mayer, according to which the temperatures decrease fromthe equator to the poles, as the squares of the sines of the latitudes,give results sufficiently precise, when the place does not differmuch in longitude from that of the regions where the empiri-cal co-efficients have been obtained. But, even in the northernhemisphere, when we apply the formula to places situated 70°or 80° to the east or west of the meridian of Paris, the calcula-ted results no longer agree with observation. The curve whichpasses through those points whose temperature is 32°, does notcoincide with any terrestrial parallel. If, in the ScandinavianPeninsula, we meet with this curve under the 65th or 68th de-
* The formula given by Mayer was T = 24 cos 2 Lat.; or T = 12 + 12 cos2 Lat. for Reaumur’s scale; and T = 84—52 sin 2 Lat., or T = 58 + 26 cos 2 Lat.for Fahrenheit’s scale. Since the publication of Humboldt’s memoir, M. Daubuissonhas resumed the subject of the earth’s temperature in his Traité de Geognosie, tom. i.p. 424. Paris, 1819. He gives the following formula, which is almost the same as thatof Mayer, for finding the mean temperature, according to the Centigrade scale, viz.T = 27° cos 2 Latitude. This formula, which is superior in accuracy to Mayer’s, givesall the temperatures in defect for latitudes below 42°, and in excess for all the higherlatitudes, as appears from Daubuisson’s table. It is therefore obviously defective.M. Daubuisson, however, considers it as applicable principally between the paral-lels of 30° and 60° of N. lat. It ought to be remarked, that in the above formula,27° has been assumed as the mean temperature of the equator, in order to make theresults agree with observations made in the temperate regions, whereas the meantemperature of the equator, as ascertained by Humboldt, is 27°.5; and if this wereused in Daubuisson’s formula, it would make the differences still more in excess.— Ed. |12| gree of latitude, it descends, on the contrary, in North America,and Eastern Asia, to the parallel of from 53° to 58°. But thedirection and the inflexions of this curve of 32° of temperatureinfluences the neighbouring isothermal lines in the same man-ner as the inflexions of the magnetic equator modify the linesof inclination. To demand what is the mean temperature, orwhat is the magnetic inclination under a particular degree of la-titude, is to propose problems equally indeterminate. Though,even in high latitudes the magnetic and the isothermal lines arenot rigorously parallel to the magnetic equator, and to the curveof 32° of temperature; yet it is the distance of any place fromthis curve which determines the mean temperature, as the in-clination of the needle depends on the magnetic latitude. These considerations are sufficient to prove, that the empiri-cal formulæ of Mayer require the introduction of a co-efficient,which depends upon the longitude, and consequently on thedirection of the isothermal lines and their nodes with the ter-restrial parallels. Mayer had no intention of disengaging theresults which he obtained from the influence of all disturbingcauses: He limited himself to the determination of the effectsof altitude above the level of the sea, and those of the seasons,and the length of the day. He wished to point out the waywhich philosophers ought to pursue in imitating the method ofastronomers. His Memoir was written at a time when we didnot know the mean temperature of three points on the globe;and the corrections which I propose after tracing the isothermallines, so far from being incompatible with the method of Mayer,are, on the contrary, among the number of those which thisgeometer seems to have indistinctly foreseen. Kirwan, in his work on Climates, and in a learned Meteoro-logical Memoir, inserted in the eighth volume of the Memoirsof the Irish Academy, attempted at first to pursue the methodproposed by Mayer, but, richer in observations than his prede-cessors, he soon perceived, that after long calculations, theresults agreed ill with observation *. In order to try a newmethod, he selected, in the vast extent of sea, those places
* Kirwan’s Estimate of the Temperature of the Globe, chap. iii.|13| whose temperature suffered no change but from permanentcauses. These were in the part of the great ocean commonlycalled the Pacific Ocean, from 40° of South to 45° of North la-titude, and in the part of the Atlantic Ocean, between the pa-rallels of 45° and 80°, from the coasts of England to the GulfStream, the high temperature of which was first determined bySir Charles Blagden. Kirwan tried to determine for everymonth the mean temperature of these seas at different degrees oflatitude; and these results afforded him terms of comparisonwith the mean temperatures observed on the solid part of the ter-restrial globe. It is easy to conceive, that this method hasno other object, but to distinguish in climates that is in the to-tal effect of calorific influences, that which is due to the imme-diate action of the sun on a single point of the globe. Kirwanfirst considers the earth as uniformly covered with a thick stra-tum of water, and he then compares the temperatures of thiswater at different latitudes, with observations, at the surface ofcontinents indented with mountains, and unequally prolongedtowards the poles. This interesting investigation may enable us to appreciate theinfluence of local causes, and the effect which arises from theposition of seas, on account of the unequal capacity of water andearth for absorbing heat. It is even better fitted for this ob-ject than the Method of Means deduced from a great numberof observations made under different meridians; but in the ac-tual state of our physical knowledge, the method proposed byKirwan cannot be followed. A small number of observationsmade far from the coasts, in the course of a month, fixes, with-out doubt, the mean annual temperature of the sea at its surface,and, on account of the slowness with which a great mass of wa-ter follows the changes of the temperature of the surroundingair, the extent of variations in the course of a month is smallerin the ocean than in the atmosphere: But it is still greatly to bedesired *, that we should be able to indicate by direct experi-ence, for every parallel, and for every month, the mean tempe-rature of the ocean under the temperate zone. The schemewhich Kirwan has formed for the extent of the seas, that ought to
* See my Relation Historique, tom. i.|14| form the term of comparison, is founded only in a small degreeupon the observations of navigators, and to a great degree onthe theory of Mayer. He has also confounded experimentsmade on the superficial temperature of the ocean with the re-sults of meteorological journals, or the indications of the tem-perature of the air which rests upon the sea: He has obvious-ly reasoned in a circle, when he modified, either by theoreticalsuppositions or by observations made on the air upon the coasts ofcontinents, the table of the temperature of the ocean, in orderto compare afterwards with these same results, partly hypothe-tical, those which observation alone furnished in the interior ofthe earth. After the works of Kirwan, we must notice thoseof Cotte, which are merely laborious, though useful, compila-tions, which, however, ought not to be used without much cir-cumspection. A critical spirit has rarely presided over the re-duction of the observations, and they are not arranged so as tolead to general results. In detailing the actual state of our knowledge on the distri-bution of heat, I have shewn how dangerous it is to confoundthe results of observation with theoretical deductions. Theheat of any point of the globe depends on the obliquity of thesun’s rays, and the continuance of their action, on the height ofthe place, on the internal heat and radiation of the earth in themiddle of a medium of variable temperature; and, in short, up-on all those causes which are themselves the effects of the rota-tion of the earth, and the inequal arrangement of continentsand seas. Before laying the foundation of a system, we mustgroup the facts, fix the numerical ratios, and, as I have alreadypointed out, submit the phenomena of heat, as Halley did thoseof terrestrial magnetism, to empirical laws. In following thismethod, I have first considered whether the method employedby meteorologists for deducing the mean temperature of theyear, the month and the day, is subject to sensible errors.Assured of the accuracy of the numerical averages, I havetraced upon a map the isothermal lines, analogous to themagnetic lines of dip and variation. I have considered themat the surface of the earth in a horizontal plane, and on thedeclivity of mountains in a vertical plane. I have examined |15| the increase of temperature from the pole to the equator, whichis inequal under different meridians; the distribution of the samequantity of heat over the different seasons, in the same isother-mal parallel, and under different latitudes; the curve of perpe-tual snows, which is not a line of equal heat; the temperatureof the interior of the earth, which is a little greater towards thenorth, and in high mountains, than the mean temperature ofthe atmosphere under the same parallel; and, lastly, the distri-bution of heat in the ocean, and the position of those bands,which may be called Bands of the warmest waters. As thelimits of this extract will not permit me to enter, in a detailedmanner, upon these different discussions, I shall confine myselfsolely to the principal results. It was formerly the custom to take the maximum and mini-mum of temperature observed in the course of a year, and toconsider half the sum as the mean temperature of the wholeyear. This was done by Maraldi, De la Hire, Muschenbröek,Celsius, and even Mairan, when they wished to compare thevery warm year of 1718 with the excessively cold years of 1709and 1740. De la Hire was struck with the identity betweenthe uniform temperature of the caves of the Observatory of Pa-ris, and the mean of the observed annual extremes. He ap-pears to have been the first who had an idea of the mean quan-tity of heat which a point of the globe receives; and he adds,“We may regard the air of the caves as the mean state of theclimate *.” Reaumur followed also the method of a maximum, though he confessed that it was incorrect †. He noticed thehours at which it was necessary to make observations; and after1735, he published in the Memoirs of the Academy the ex-tremes of daily temperature: he even compared the produce oftwo harvests with the sum of the degrees of heat to which duringtwo consecutive years the crops had been exposed. When hetreated, however, of the mean temperature of the month, hecontented himself, as Duhamel did thirty years afterwards,with recording three or four thermometrical extremes. In orderto have some idea of the errors of this imperfect method, I may
* Mem. de l’Acad. 1719, p. 4.† Id. 1735, p. 559.|16| state, that even in 1777, the mean temperature of Toulon wasestimated by Cotte * at 78°.08, though he afterwards found, byemploying the whole mass of observations, that it was not morethan 60°.26. In order to diminish the errors of the method of annual ex-tremes, it was perceived, though very late, that it was necessaryto subdivide the curve which expresses the variation of tempe-rature. Twenty-four extremes divided among twelve monthsof the year, give an annual mean more exact than the two ex-tremes of all the observations. The ordinates do not increaseuniformly and uninterruptedly up to the maximum of the year,and there are partial inflexions sufficiently regular. The morewe subdivide, and the more we know the terms in the series,the more will these terms approximate, and the less error willthere be in the supposition of an arithmetical progression, andin that of the equidistance of the different maxima and minima of temperature. These considerations enable us to appreciatethe three methods according to which observations are at presentmade. 1. Observations are made three times a-day, at sunriseand sunset, and at two o’clock in the afternoon. This was doneat Geneva during the three years 1796, 1797 and 1798. In theobservations, the hour of mid-day was preferred to that of sunset.2. Observations are made twice every day, at the two periodswhich are supposed to give the maximum and the minimum,namely, at sunrise, and at two o’clock in the afternoon. 3. Ob-servations are made once a-day, at an hour which, in differentseasons, has been found to represent the mean temperature ofthe day. It is thus that M. Raymond, by a judicious induc-tion, has proved, that the height of the barometer, at mid-day,gives, in our climates, the mean atmospherical pressure, correct-ed for the diurnal variation. In calculating † a great number of observations made be-tween the parallels of 46° and 48°, I have found, that a singleobservation at sunset, gives a mean temperature which differsonly some tenths of a degree from that which is deduced fromobservations made at sunrise and at two o’clock. The devia-
* Mem. de la Soc. Royale de Med. 1777, p. 104.† De la Formule Barom. p. 213.|17| tions of different months, do not exceed 1°.8, and they are veryregularly positive or negative, according to the order of the sea-sons. M. Arago * has examined for seven years the observationsof noon. They give for Paris 5°.4 more than the mean tempera-ture of the whole year. Upon high mountains in the tempe-rate zone, the difference is scarcely 1°.8 †. By the applicationof coefficients, variable according to the latitude and the eleva-tion, we may deduce the true mean temperatures from observa-tions made at any particular period of the day, nearly in thesame manner as we can ascertain the latitude of a place fromaltitudes of the sun, taken out of the meridian. If we do not stop at two observations of the maximum andminimum, but add a third observation, we commit an error moreor less serious, if we divide simply by three the sum of the ob-servations, without attending to the duration of the partial tem-peratures, and to the place which the third observation occupiesbetween the last terms of the series ‡. Experience proves, thatthe mean temperatures of the year, obtained by two or three ob-servations, do not differ sensibly, if the intermediate observationis sufficiently distant (four or five hours) from the observationof the maximum and minimum. Whenever, therefore, we donot take into account the duration of the intermediate tem-peratures, we should prefer the two observations of the ex-treme temperature, which is the method most generally adopted.We shall content ourselves with pointing out the errors to which
* The mean of the observations at noon at Paris was 56°.84; at Clermontin Auvergne (elevation 1348 feet), 56°,30; at Strasburg (elevation 453 feet),55°.22. Bulletin de la Soc. Philom. 1814, Oct. p. 95.—H.† At the Hospice of St Gothard. Ephem. Soc. Pal. 1785, p. 47.‡ Example.—On the 13th June, at 4h in the morning, 46°.4; at 2h in the af-ternoon, 55°.4; and at 11h in the evening, 50°, (erroneously 46°.4, or 8° Centig.in the original). In calculating by the duration, we have
| 50°.9 | the mean for | 10h | of interval, | = 509°.0 |
| 52.7 | 9 | = 474.3 | ||
| 48.2 | 5 | = 241.0 |
* Example.—At sunrise at 6h, 50°; at 2 o’clock in the afternoon, 62°.6. Atsunset, 51°.8; at 2h, 66°.2; at sunrise, 50°. The true means will be for the first24 hours 56°.9, and for the second 59°.0, for we shall have
- For 8h, \( \frac{1}{2} \) (50°.0 + 66°.2) × 8 = 450°.4 for 8h = 472°.0
- 16 \( \frac{1}{2} \) (51°.8 + 62°.6) × 16 = 915°.2 for 16h = 929°.6
* On the 3d and 4th September 1811, lat. 48°.50′.
| Sum of the temperaturesduring 24 hours. | True mean temperature,taking into account theduration. | Half sum of the two ex-treme temperatures. |
| 625°.71 Fahr. | 57°.92 Fahr. | 58°.28 Fahr. |
| 672.49 | 59.90 | 61.88 |
| 834.67 | 66.74 | 65.12 |
| 834.67 | 66.74 | 68.00 |
| 835.37 | 66.74 | 63.50 |
| ——— | ——— | |
| 63.61 Mean. | 63.35 Mean. |
* Example.—Latitude 10°.25′.
| Calculation of atrue mean bythe duration. | Supposition ofan arithmeticalprogression. | ||
| Before the maximum, | 11th September 1799, | 70°.52 Fahr. | 69°.44 Fahr. |
| 14th | 69.26 | 68.00 | |
| 18th | 71.24 | 70.34 | |
| After the maximum, | 18th August, | 68.72 | 69.80 |
| 20th | 70.16 | 71.24 | |
| 27th | 68.72 | 69.26 | |
| Before the maximum, | 17th August, | 69.26 | 68.00 |
| After the maximum, | 17th August | 65.48 | 66.02 |
| ——— | ——— | ||
| Total effect, | 17th August, | 67.37 | 67.01 |
— On Isothermal Lines, and the Distribution ofHeat over the Globe. By Baron Alexander de Hum-boldt. (Continued from Vol. III. p. 20.)
| Lat. | MeanTemp. | ||
| I. Parallels of Georgia, of the Stateof Mississippi, of Lower Egypt,and Madeira. | Natches, ‒ | 31°28′ | 64° 8′ |
| Funchal, ‒ | 32 37 | 68 7 | |
| Orotava, ‒ | 28 25 | 69 8 | |
| Rome, ‒ | 41 53 | 60 4 | |
| Algiers, ‒ | 36 48 | 70 0 | |
| ——— | ——— | ||
| Difference, | 7 0 | 4 1 | |
| Lat. | MeanTemp. | ||
| II. Parallels of Virginia, Kentucky,Spain, and the South of Greece. | Williamsburg, | 38° 8′ | 58° 0′ |
| Bourdeaux, | 44 50 | 56 5 | |
| Montpellier, | 43 36 | 59 4 | |
| Rome, ‒ | 41 53 | 60 4 | |
| Algiers, ‒ | 36 48 | 70 0 | |
| ——— | ——— | ||
| Difference, | 7 0 | 7 7 | |
| III. Parallels of Pennsylvania, Jersey,Connecticut, Latium, and Ro-melia. | Philadelphia, | 39 56 | 54 9 |
| New-York, | 40 40 | 53 8 | |
| St Malo, ‒ | 48 39 | 54 5 | |
| Nantes, ‒ | 47 13 | 54 7 | |
| Naples, ‒ | 40 50 | 63 3 | |
| ——— | ——— | ||
| Difference, | 7 0 | 9 5 | |
| Ipswich, ‒ | 42 38 | 50 0 | |
| Cambridge (Amer.) | 42 25 | 50 4 | |
| Vienna, ‒ | 48 13 | 50 5 | |
| Manheim, ‒ | 49 29 | 51 3 | |
| Toulon, ‒ | 43 7 | 62 1 | |
| Rome, ‒ | 41 53 | 60 4 | |
| ——— | ——— | ||
| Difference, | 6 30 | 11 0 | |
| IV. Parallels of Canada, Nova Scotia,France, and the South of Ger-many. | Quebec, ‒ | 46 47 | 41 9 |
| Upsal, ‒ | 59 51 | 41 9 | |
| Padua, ‒ | 45 24 | 57 7 | |
| Paris, ‒ | 48 50 | 51 4 | |
| ——— | ——— | ||
| Difference, | 13 0 | 12 6 | |
| V. Parallels of Labrador, the Southof Sweden, and Courland. | Nains, ‒ | 57 0 | 26 4 |
| Okak, ‒ | 57 20 | 29 8 | |
| Umea, ‒ | 63 50 | 33 3 | |
| Enontekies, | 68 30 | 27 0 | |
| Edinburgh, | 55 58 | 47 8 | |
| Stockholm, | 59 20 | 42 3 | |
| ——— | ——— | ||
| * Difference, | 11 0 | 17 1 | |
* The differences under the column of latitudes, is the difference of the latitudeof a place in Europe and a place in America, which have the same mean tempera-ture; and the differences under the column of mean temperatures, is the differenceof the mean temperatures of a place in Europe and a place in America, whichhave the same latitude.—Ed. † See my Prolegomena de distributione geographica plantarum, secundum cœlitemperiem et altitudinem montium. p. 68.—H.|258| order to find the same quantity of annual heat as in America. As a place could not be found in the Old World, whose meantemperature was 48° the same as that of Williamsburg, I havesupplied it with an interpolation between the latitudes of twopoints whose mean temperatures are 56°.5 and 59°.4. By ananalogous method, and by employing only good observations, Ihave found that 1. The isothermal line of 32° (0° centig.) passes between Uleo and Enontekiesin Lapland (lat. 66° to 68°; East long. from London 19° to 22°), and Table Bay inLabrador (lat. 54° 0′, west long. 58°.) 2. The isothermal line of 41° (5° centig.) passes by near Stockholm (lat. 60°east long. 18°) and the Bay of St George in Newfoundland (lat. 48°, and long. 59°.) 3. The isothermal line of 50° (10° centig.) passes by Belgium (lat. 51°, east long.2°) and near Boston (lat. 42° 30′, west long. 70° 59.) 4. The isothermal line of 59° (15° centig.) passes between Rome and Florence(lat. 43° 0′, east long. 11° 40′) and near Raleigh in North Carolina (lat. 36° 0′, andwest long. 76° 30′.) The direction of these lines of equal heat, gives for the twosystems of temperature, which we know by precise observations,viz. part of the middle and west of Europe, and that of thecoast of America, the following differences:
| Latitude. | Mean Temp. of the westof the Old World. | Mean Temp. of the eastof the New World. | Difference. |
| 30 | 70°.52 | 66°.92 | 3°.60 |
| 40 | 63.14 | 54.50 | 8.64 |
| 50 | 50.90 | 37.94 | 12.96 |
| 60 | 40.64 | 23.72 | 16.92 |
| Latitude. | Temp. | Temp. | |||
| From | 0°—20° | In the OldWorld, | 3°.6 | In the New World, | 3°.6 |
| 20 — 30 | 7.2 | 10.8 | |||
| 30 — 40 | 7.2 | 12.6 | |||
| 40 — 50 | 12.6 | 16.2 | |||
| 50 — 60 | 9.9 | 13.3 | |||
| 0 — 60 | 40.5 | 56.5 | |||
* This observation relates to the Centigrade scale. If we count the tempera-tures from 32°, it applies also to Fahrenheit’s scale.—Ed. |259| 40° and 45°. Observation here presents a result entirely con-formable to theory, for the variation of the square of the cosine,which expresses the law of the temperature, is a maximum to-wards 45° of latitude. This circumstance ought to have a favour-able influence on the civilization and industry of the peoplewho inhabit the regions under this mean parallel. It is thepoint where the regions of the vines touch those of the olivesand the citrons. On no other part of the globe, in advancingfrom north to south, do we observe the temperatures increasemore sensibly, and no where else do vegetable productions, andthe various objects of agriculture, succeed one another withmore rapidity. But a great difference in the productions ofcontiguous countries, gives activity to commerce, and augmentsthe industry of the cultivators of the soil. We have traced the direction of the isothermal lines fromEurope to the Atlantic Provinces of the New World. Wehave seen them approach one another from parallelism towardsthe south, and converge towards the north, particularly be-tween the thermometric curves of 41° and 50°: We shall nowendeavour to pursue them to the west. North America pre-sents two chains of mountains, extending from N. E. to S. W.,and from N. W. to S. E. forming almost equal angles with themeridian, and nearly parallel to the coasts which are oppositeto Europe and Asia, viz. the chain of the Alleghanys and the Rocky Mountains, which divide the waters of the Missouriand the Columbia. Between these chains stretch the vast ba-sin of the Mississippi, the plains of Lousiana, and of the Tenes-see, and the states of Ohio, the centre of a new civilization. Itis generally believed in America that the climate is more mildto the west of the Alleghany Mountains, than under the sameparallels in the Atlantic States *. Mr Jefferson, has estimatedthe difference at 3° of latitude; and the Gleditsia monosperma, the Catalpa, and the Aristolochia Sypho, and other vegetableproductions, are found so many degrees farther to the north, inthe basin of the Ohio, than on the coast of the Atlantic †.
* This is true also of the Columbian Valley. See Warden’s Account of theUnited States, vol. iii. p. 169.—Ed. † See my Essai sur la Geographie des Plantes, p. 154.|260| M. Volney has endevoured to explain these phenomena by thefrequency of the south-west winds, which drive back the warmair of the Gulf of Mexico towards these regions. A series ofgood observations, made for seven years by Colonel Mansfieldat Cincinnati, on the banks of the Ohio, and recently publish-ed by Mr Drake, in an excellent treatise on American meteoro-logy *, has removed the doubts which obscured this point. Thethermometrical means prove that the isothermal lines do notrise again in the regions of the west. The quantity of heatwhich each point of the globe receives under the same parallels,is nearly equal on the east and the west of the Alleghany range,the winters being only a little milder to the west, and the sum-mers a little warmer †. The migrations of vegetables towardsthe north are favoured in the basin of the Mississippi, by theform and the direction of the valley which opens from thenorth to the south. In the Atlantic Provinces, on the contra-ry, the valleys are transverse, and oppose great obstacles to thepassage of plants from one valley to another. If the isothermal lines remain parallel, or nearly so, to theequator, from the Atlantic shores of the New World to the eastof the Mississippi and the Missouri, it cannot be doubted thatthey rise again beyond the Rocky Mountains, on the oppositecoast of Asia, between 35° and 55° of latitude. To the consi-
* Natural and Statistical View or Picture of Cincinnati and the Miami Coun-try, 1 vol. 8vo. Cincinnati.—H. See Warden’s Account of the United States, vol. ii. 236 for an abstract of Mr Drake’s results.—Ed. † The following comparison of the mean temperatures has been deduced withgreat care. |Spaltenumbruch|
| Cincinnati. Lat. 36° 6′, west long. 84° 24′. | |
| Winter, | 32°.9 Fahr. |
| Spring, | 54.1 |
| Summer, | 72.9 |
| Autumn, | 54.9 |
| —— | |
| Mean, | 53.7 |
| Philadelphia. Lat. 39° 56′, west long. 75° 16′. | |
| Winter, | 32°.2 Fahr. |
| Spring, | 51.4 |
| Summer, | 73.9 |
| Autumn, | 56.5 |
| —— | |
| Mean, | 53.5 |
* Essai Politique sur la Nouvelle Espagne, tom. ii. p. 440, 478, 509.† On account of the influence of west and south-west winds. See Dalton’s Meteor. Observ. p. 125.‡ In comparing places from the west to the east, and nearly under the sameparallel, we find, |Spaltenumbruch|
| West. | Lat. | MeanTemp. |
| St Malo, | 48° 39′ | 54°.5 |
| Amsterdam, | 52 21 | 53.4 |
| Naples, | 40 50 | 63.3 |
| Copenhagen, | 55 41 | 45.7 |
| Upsal, | 59 52 | 41.9 |
| East. | Lat. | MeanTemp. |
| Vienna, | 48° 13′ | 50°.5 |
| Warsaw, | 52 14 | 48.6 |
| Pekin, | 39 54 | 54.9 |
| Moscow, | 55 46 | 40.1 |
| Petersburgh, | 59 56 | 38.8 |
* |Spaltenumbruch|
| Lat. | MeanTemp. | |
| Bologna, | 44° 29′ | 56°.3 |
| Genoa, | 44 25 | 60.6 |
| Lat. | MeanTemp. | |
| Marseilles, | 43° 17′ | 58°.8 |
| Rome, | 41 53 | 60.4 |
| Old World. | Lat. | Mean Temp. |
| Senegambia, | 15° 0 | 79°.07 |
| Madras, | 13 5 | 80 .42 |
| Batavia, | 6 12 | 80 .42 |
| Manilla, | 14 36 | 78 .08 |
| New World. | Lat. | Mean Temp. |
| Cumana, | 10° 27′ | 81°.86 |
| Antilles, | 17 0 | 81.05 |
| Vera Cruz, | 19 11 | 78.08 |
| Havannah, | 23 10 | 78.08 |
| Cisatlantic Region. Long. 1° W. and 17° E. | Transatlantic Region. Long. 58°—72° W. | |||||
| Isother-malLines of | Mean Temperature. | Mean Temperature. | ||||
| Winter. | Summer. | Diff. | Winter. | Summer. | Diff. | |
| 68° | 59°.0 | 80°.6 | 21°.6 | 53°.6 | 80°.6 | 27°.0 |
| 59 | 44.6 | 73.4 | 28.8 | 39.2 | 78.8 | 39.6 |
| 50 | 35.6 | 68.0 | 32.4 | 30.2 | 71.6 | 41.4 |
| 41 | 24.8 | 60.8 | 36.0 | 14.0 | 66.2 | 52.2 |
| 32 | 14.0 | 53.6 | 39.6 | 1.4 | 55.4 | 54.0 |
| Cisatlantic Region. Long. 31° E. and 22° W. | ||||
| Places. | Latitude. | Mean Temperature. | ||
| Whole Year. | Winter. | Summer. | ||
| (Pondicherry) | 11°.55 | 85°.3 | 77°.0 | 90°.5 |
| Cairo, | 30 02 | 72.7 | 57.7 | 84.7 |
| Funchal, | 32 37 | 68.7 | 63.9 | 72.5 |
| Rome. | 41 53 | 60.4 | 45.9 | 55.2 |
| Bourdeaux, | 44 50 | 56.5 | 42.1 | 70.7 |
| Paris, | 48 50 | 51.4 | 38.3 | 66.2 |
| Copenhagen, | 55 41 | 45.7 | 30.7 | 64.6 |
| Stockholm, | 59 20 | 42.3 | 25.5 | 61.9 |
| Drontheim, | 63 24 | 39.9 | 24.7 | 61.3 |
| Umeo, | 63 50 | 33.3 | 12.9 | 54.9 |
| Transatlantic Region. Long. 69° E. and 99° W | ||||
| Places. | Latitude. | Mean Temperature. | ||
| Whole Year. | Winter. | Summer. | ||
| Cumana, | 10°.27 | 81°.9 | 81°.7 | 83°.7 |
| Havannah, | 23.10 | 78.1 | 71.2 | 83.3 |
| Natchez, | 31.28 | 64.8 | 48.6 | 79.2 |
| Cincinnati, | 39.06 | 53.6 | 32.9 | 72.9 |
| Philadelphia, | 39 56 | 54.9 | 32.2 | 73.9 |
| New York, | 40.40 | 53.8 | 29.8 | 79.2 |
| Cambridge, | 42.25 | 50.4 | 34.0 | 70.5 |
| Quebec, | 46.47 | 41.9 | 14.2 | 68.0 |
| Nain, | 57.10 | 26.4 | 0.6 | 48.4 |
| Fort Churchhill, | 59.02 | 25.3 | 6.8 | 52.2 |
| Places. | Lat. | Mean Temperature. | Diffe-rence. | Observations. | |
| ColdestMonth. | WarmestMonth. | ||||
| Cumana, | 10° 27 | 80°.1 | 84°.4 | 4°.3 | Uninterrupted trade winds. |
| Pondicherry, | 11 55 | 76.1 | 91.4 | 15.3 | Monsoons. Radiation of the sands. |
| Manilla, | 14 36 | 68.0 | 86.9 | 18.9 | Monsoons. |
| Vera Cruz, | 19 11 | 70.0 | 81.7 | 11.7 | North winds in winter. |
| Cape Français, | 19 46 | 77.0 | 86.0 | 9.0 | Uninterrupted trade winds. |
| Havannah, | 23 10 | 70.0 | 83.8 | 13.8 | North winds in winter. |
| Funchal, | 32 37 | 64.0 | 75.6 | 11.6 | Insular climate. |
| Natchez, | 31 28 | 46.9 | 78.8 | 31.9 | Transatlantic region. Interior. |
| Cincinnati, | 39 6 | 29.6 | 74.4 | 44.8 | Same system of climate. |
| Pekin, | 39 54 | 24.8 | 84.2 | 59.4 | Region of eastern Asia. |
| Philadelphia, | 39 56 | 29.8 | 77.0 | 47.2 | Transatlant. region. Eastern coasts |
| New York, | 40 40 | 25.3 | 80.8 | 55.5 | Idem. |
| Rome, | 41 53 | 42.1 | 77.0 | 34.9 | Cisatlantic region. |
| Milan, | 45 28 | 33.8 | 55.2 | 21.4 | Interior land. |
| Buda, | 47 29 | 27.7 | 71.6 | 43.9 | Idem. |
| Paris, | 48 50 | 35.1 | 69.8 | 34.7 | Nearer the western coast. |
| Quebec, | 46 47 | 14.0 | 73.4 | 59.4 | Transatlant. region. Eastern coasts. |
| Dublin, | 53 21 | 37.6 | 60.3 | 22.7 | Region of the west of Europe.Insular climate. |
| Edinburgh, | 55 58 | 38.3 | 59.4 | 21.1 | Idem. |
| Warsaw, | 52 14 | 27.1 | 70.3 | 43.2 | Interior land. |
| Petersburg, | 59 56 | 8.6 | 65.7 | 57.1 | East of Europe. |
| North Cape, | 71 0 | 22.1 | 46.6 | 24.5 | Climate of coasts and islands. |
* Political Essay on the Kingdom of New Spain, tom. iv. p. 528.† Leopold von Buch’s Travels in Lapland, tom. ii.|268| the Atlantic region of the United States, exhibits excessive cli-mates, and seasons strongly contrasted, while the coasts of NewCalifornia, and the embouchure of the Colombia, have wintersand summers almost equally temperate. The meteorologicalconstitution of these countries in the N. W. resembles that ofEurope as far as 50° or 52° of latitude; and without wishing toascribe the great revolutions of our species solely to the influ-ence of climate, we may affirm that the difference between theeastern and western shores of continents, has favoured the an-cient civilisation of the Americans of the west,—facilitated theirmigrations towards the south, and multiplied those relations witheastern Asia, which appear in their monuments, their religion,traditions, and the division of the year. In comparing the twosystems of climates, the concave and convex summits of thesame isothermal lines, we find at New York the summer of Rome and the winter of Copenhagen;—at Quebec the summerof Paris and the winter of Petersburg. In China, at Pekin for example, where the mean temperature of the year is that ofthe coasts of Britanny, the scorching heats of summer are great-er than at Cairo, and the winters as rigorous as at Upsal. The mean temperature of the year being equal to the fourthpart of the winter, spring, summer and autumnal temperatures,we shall have upon the same isothermal line of 53°6′ (12° cent.)
-
- At the concave summit in America, 74° 40′ west long.
-
- At the convex summit in Europe, 2° 20′ west long.
-
- At the concave summit in Asia,116° 20′ east long.
| Long. | Lat. | Mean Temperature. | |||
| Winter. | Summer. | ||||
| Isoth. Lineof 68°. | 82° 10′ W. | 29° 30 | Florida, | 53°.6 | 80°.6 |
| 16 56 W. | 32 37 | Madeira, | 63.5 | 72.0 | |
| 3 0 E. | 36 48 | North Africa, | 59.0 | 80.6 | |
| Isoth. Lineof 63°.5 | 89 40 W. | 32 30 | Mississippi, | 46.4 | 77.0 |
| 14 11 E. | 40 50 | Italy, | 50.0 | 77.0 | |
| Isoth. Lineof 59°. | 84 10 W. | 35 30 | Basin of the Ohio, | 39.2 | 77.9 |
| 3°—4° E. | 43 30 | Middle of France, | 44.6 | 75.2 | |
| Isoth. Lineof 54°.5 | 84 40 W. | 38 30 | America, W. of Allegh. | 34.7 | 75.2 |
| 74 10 W. | 40 0 | America, E. of ditto. | 32.5 | 77.0 | |
| 1 32 W. | 47 10 | West of France, | 39.0 | 68.0 | |
| 9 20 E. | 45 30 | Lombardy, | 34.7 | 73.4 | |
| 116 20 E. | 40 0 | East of Asia, | 26.6 | 82.4 | |
| Isoth. Lineof 50°. | 84 20 W. | 41 20 | America, W. of Allegh. | 31.1 | 71.6 |
| 71 10 W. | 42 30 | America, E. of ditto. | 30.2 | 73.4 | |
| 6 40 W. | 52 30 | Ireland, | 39.2 | 59.5 | |
| 0 40 W. | 53 30 | England, | 37.4 | 62.6 | |
| 2 20 E. | 51 0 | Belgium, | 36.5 | 63.5 | |
| 19 0 E. | 47 30 | Hungary, | 31.1 | 69.8 | |
| 116 20 E. | 40 0 | Eastern Asia, | 23.0 | 78.8 | |
| Isoth. Lineof 45°.5. | 71 0 W. | 44 42 | America, E. of Allegh. | 23.9 | 71.6 |
| 2 10 W. | 57 0 | Scotland, | 36.1 | 56.5 | |
| 12 35 E. | 55 40 | Denmark, | 30.3 | 62.6 | |
| 21 20 E. | 53 5 | Poland, | 28.0 | 66.2 | |
| Isoth. Line41°. | 71 10 W. | 47 0 | Canada, | 14.0 | 68.0 |
| 9 20 E. | 62 45 | West of Norway, | 24.8 | 62.6 | |
| 17 20 E. | 60 30 | Sweden, | 24.8 | 60.8 | |
| 24 20 E. | 60 0 | Finland, | 23.0 | 63 5 | |
| 36 20 E. | 58 30 | Central Russia, | 22.1 | 68.0 | |
| Isoth. Lineof 36°.5. | 71 40 W. | 50 0 | Canada, | 6.8 | 60.8 |
| 18 5 E. | 62 30 | West coast of Gulf ofBothnia, | 17.6 | 57.2 | |
| 22 20 E. | 62 50 | East coast of ditto. | 16.5 | 59.0 | |
| Isoth. Lineof 32°. | 57 40 E. | 53 0 | Labrador, | 3.2 | 51.8 |
| 19 50 E. | 65 0 | Sweden, | 11.3 | 53.6 | |
| 25 20 E. | 71 0 | North Extremity of Nor-way, | 23.9 | 43.7 | |
* Drake’s Nat. and Statist. View of Cincinnati, p. 63.|270| When we consider that the annual temperature of a place isnothing more than the numerical expression of the mean of theordinates, we may imagine an infinity of entirely dissimilarcurves, in which the twelve ordinates of the months have exact-ly the same mean. This consideration should not lead us tobelieve, that a place which has the winter of the south ofFrance, that is, where the mean temperature of winter is 44°.6,may, by the compensation of a summer and an autumn, muchless warm, have the mean temperature of Paris. It is true, thatthe constant ratio which is observed in the same parallel, be-tween the solstitial heights of the sun and the semidiurnal arcs,is differently modified by the position of a place in the centre ofa continent or upon the coast, by the frequency of certainwinds, and by the constitution of an atmosphere more or lessfavourable to the transmission of light, and of the radiating ca-loric of the earth. But these variations, which travellers haveoften exaggerated, have a maximum which nature never over-steps. It is impossible to examine the preceding table withoutobserving, that the division of the annual heat between summerand winter, follows on each isothermal line a determinate type;that the deviations of that type are contained between certain li-mits, and that they obey the same law in the zones which passby the concave or convex summits of the isothermal lines, forexample, by 58°—68° of West Long., and by 5°—7°, and 116°of East Longitude. The following table shews the oscillations, or the maxima and minima, observed in the division of the heat between the sea-sons. I have added the means of the winters and summersfound at different degrees of longitude, and under the same iso-thermal line.
| Isoth.Lines. | Degrees ofLong. exa-mined. | Oscillations observed in theMeans. | Means calculated. | ||
| Winters. | Summers. | Winters. | Summers. | ||
| 32° | 83 | 3°.2 to 24°.8 | 51°.8 to 53°.6 | 14°.0 | 52°.7 |
| 41 | 107 | 14.0 24.8 | 62.6 68.0 | 19.4 | 65.3 |
| 50 | 200 | 23.0 37.4 | 62.6 78.8 | 30.2 | 70.7 |
| 59 | 87 | 39.0 44.6 | 75.2 77.0 | 41.9 | 75.2 |
| 68 | 84 | 53.6 59.0 | 71.6 80.6 | 56.3 | 77.9 |
| To | 59°.0 | The wintersare from | 44°.6 | to | 46°.4 | and the sum-mers from | 73°.0 | to | 75°.2 |
| 54.5 | 36.5 | 41.0 | 68.0 | 73.0 | |||||
| 50.0 | 31.1 | 37.4 | 62.6 | 69.8 | |||||
| 45.5 | 28.4 | 36.1 | 57.2 | 68.0 | |||||
| 41.0 | 20.3 | 26.8 | 55 4 | 66.2 |
* Throughout all Holland, 90 days of winter have a mean temperature of from36°.7 to 38°.7. At Milan, at Padua, and at Verona, the same season is only from34°.7 to 36°.7. The observations made in Belgium and Holland, offer also avery remarkable example of an equal quantity of heat distributed in the space of ayear over a vast extent of territory. The mean temperatures scarcely vary fromParis to Franecker, over 3\( \frac{1}{2} \) degrees of latitude, which, in the interior of a continent,should produce a difference of 3\( \frac{1}{4} \) degrees of annual temperature. The canal of theChannel opens towards the north. The west winds blow, therefore, over a great|272| 45° 28′, and isothermal latitude 55° 8′,) and in a great part ofLombardy. Farther to the north, in the Scandinavian Penin-sula, we meet with three very different systems of climate, viz.1. The region of the west coasts of Norway to the west of themountains. 2. The region of the eastern coasts of Sweden, tothe east of the mountains. And, 3. The region of the westcoasts of Finland, along the Gulf of Bothnia. Baron Von Buchhas made us acquainted with the atmospherical constitution ofthese three different regions, in which the slowest increase ofthe winter cold is felt from Drontheim to the North Cape,on the west and north-west coasts. At the Isle of Mageroe,(in north lat. 82°,) at the northern extremity of Europe, underthe parallel of 71°, the winters are still 7°.2 milder than at StPetersburg, (in north lat. 38°.8,) but the mean heat of thesummers never reaches that of the winters of Montpellier, (innorth lat. 59°.4). At the Faroe Isles, under 62° of north lat.the lakes are very seldom covered with ice, and to so temperatea winter succeeds a summer, during which snow often falls uponthe plains. Nowhere without the tropics is the division of theannual heat among the seasons more equal. In the temperatezone, under parallels nearer to our own, Ireland presents an ex-
part of the ocean, and during a long rainy winter, with the sky almost alwaysclouded, the surface of the earth is less cooled by radiation than farther to the east,in the interior of the country, where the atmosphere is pure and dry.
| Lat. | Mean Temperature. | |||
| Year. | Winter. | Summer | ||
| Franecker, | 52° 36′ | 51°.8 | 36°.7 | 67°.3 |
| Amsterdam, | 52 22 | 53.4 | 36.9 | 65.8 |
| Hague, | 52 3 | 51.8 | 38.3 | 65.5 |
| Rotterdam, | 51 54 | 51.1 | 36.9 | 64.9 |
| Middelburg, | 51 30 | 49.6 | 36.1 | 64.0 |
| Dunkirk, | 51 2 | 50.5 | 38.5 | 64.0 |
| Brussels, | 50 50 | 52.0 | 36.7 | 66.2 |
| Arras, | 50 17 | 49.4 | 35.8 | 63.3 |
| Cambray, | 50 10 | 52.0 | 39.0 | 66.6 |
| Mean Temp. | |
| Milan, | 55°.8 |
| Padua, | 56.3 |
| Verona, | 55.8 |
| Mean Temp. | |
| Bologna, | 56°.3 |
| Venice, | 56.5 |
* Wahlenberg, Flora Carpath. p. 90.† Irish Transactions, tom. viii. p. 116, 203, 269.|274| 51°.8, and 53°.6,) corresponding to the parallels of 45° and 47°,tend to raise the lines of equal summer or the isotheral curves. However great be the influence of the unequal division of theheat between the seasons, on the physical condition of nations, onthe developement of agricultural industry, and the selectionof plants for culture, I would not recommend the tracing up-on the same chart the isothermal lines, and the winter and sum-mer curves. This combination would not be more fortunatethan the lines of declination, inclination, and equal intensity ofthe magnetic forces, which, however, all depend upon one ano-ther. Instead of multiplying the intersection of the curves, itwill be sufficient to add to the isothermal lines, near their sum-mits, the indication of the mean temperatures of summer andwinter. In this way, by following the line of 50°, we shall findmarked in America, to the west of Boston, \( \left(\frac{30^\circ.2}{73^\circ.4}\right) \), in Eng-land \( \left(\frac{37^\circ.4}{62^\circ.6}\right) \), in Hungary \( \left(\frac{31^\circ.1}{69^\circ.8}\right) \), and in China \( \left(\frac{23^\circ.0}{78^\circ.8}\right) \). (To be continued.)
On Isothermal Lines, and the Distribution of HeatOver the Globe. By Baron Alexander de Humboldt. (Continued from Vol. III. p. 274.)
* In cases like the present, we have not used the round numbers of Fahrenheit,as is done in the original with the Centigrade scale, but have given the real valueof the degrees used by the author, that his exact numbers may always be ascertain-ed.—Ed. |24| 35°.6, and that the thermometer sometimes sinks there even du-ring several days from 14° to 10°.4. The region of potable winesextends in Europe between the isothermal lines of 62°.6 and 50°,which correspond to the latitudes of 36° and 48°. The culti-vation of the vine extends, though with less advantage, even tocountries whose annual temperature descends to 48°.2 and to47°.48; that of winter to 33°.8, and that of summer to 66°.2and 68°. These meteorological conditions are fulfilled in Eu-rope as far as the parallel of 50°, and a little beyond it. InAmerica, they do not exist farther north than 40°. They havebegun, indeed, some years ago to make a very good red wineto the west of Washington, beyond the first chain of mountains,in the valleys which do not extend beyond 38° 54′ of Lat. On theContinent of Western Europe, the winters, whose mean tempe-rature is 32°, do not commence till on the isothermal lines of48°.2 and 50°, in from 51° to 52° of latitude; while in America,we find them already on the isothermal lines of from 51°.8 to53°.6, under from 40° to 41° of latitude. If, instead of considering the natural inflexions of the isother-mal lines, that is to say, those that propagate themselves pro-gressively at great intervals of longitude, we direct our atten-tion to their partial inflexions, or to particular systems of cli-mates occupying a small extent of country, we shall still findthe same variations in the division of the annual heat betweenthe different seasons. These partial inflexions are most remark-able, 1st, In the Crimea, where the climate of Odessa is contrastedwith that of the S.W. shores of the Chersonesus, sheltered bymountains, and fit for the cultivation of the olive and the orangetree. 2dly, Along the Gulf of Genoa, from Toulon and the HieresIsles to Nice and Bordighera, (Annales du Museum, tom. xi.p. 219.), where the small maritime palm-tree, Chamærops, grows wild, and where the date-tree is cultivated on a largescale, not to obtain its fruit, but the palms or etiolated leaves. 3dly, In England, on the coast of Devonshire, where the portof Salcombe has, on account of its temperate climate, been call-ed the Montpellier of the North, and where (in South Hams) theMyrtle, the Camellia Japonica, the Fuchsia coccinea, and the |25| Buddleia globosa *, pass the winter in the open ground, andwithout shelter. 4thly, In France, on the western coasts of Normandy and Brit-tany. In the Department of Finisterre, the arbutus, the pome-granate-tree, the Yucca gloriosa and aloifolia, the Erica Medi-terranea, the Hortensia, the Fuchsia, the Dahlia, resist in openground the inclemency of a winter which lasts scarcely fifteen ortwenty days, and which succeeds to a summer by no meanswarm. During this short winter, the thermometer sometimesfalls to 17°.6. The sap ascends in the trees from the month ofFebruary; but it often freezes even in the middle of May.The Lavatera arborea is found wild in the isle of Glenans, andopposite to this island, on the continent, the Astragalus Bajon-ensis, and the Laurus nobilis †. From observations made in Brittany for twelve years, atSt Malo, at Nantes, and at Brest, the mean temperature of thepeninsula appears to be above 56°.3. In the interior of France,where the land is not much elevated above the sea, we must de-scend 3° of latitude in order to find an annual temperature likethis. It is known from the researches of Arthur Young ‡, that inspite of the great rise of the two isothermal lines of 53°.6 and55°.4 on the western coast of France, the lines of culture (thoseof the olive, and of the maize and vine,) have a direction || quiteopposite, from S.W. to N.E. This phenomenon has been as-cribed §, with reason, to the low temperature of the summers
* Knight, Trans. Hort. Soc. vol. i. p. 32. In 1774, an Agave flowered atSalcombe, after having lived twenty-eight years without being covered in winter.On the coast of England, the winters are so mild, that orange trees are seen onespaliers, which are sheltered, as at Rome, only by means of a matting.—H.† Bonnemaison, Geogr. Botan. du Depart. du Finisterre, (Journal de Botan. tom. iii. p. 118.)‡ Travels in France, vol. ii. p. 91.|| The line which limits the cultivation of the vine, extends from the embou-chure of the Loire and of the Vilaine, by Pontoise, to the confluence of the Rhineand the Moselle. The line of the olive trees commences to the west of Narbonne,passes between Orange and Montelimart, and carries itself to the N.E. in the di-rection of the Great St Bernard.—H.§ Decandolle, Flor. Franç. 3d edit. tom. ii. pl. viii. xi. Lequinio, Voy. dans.le Jura, tom. ii. p. 84.—91.|26| along the coast; but no attempt has been made to reduce to nu-merical expressions the ratios between the seasons in the inte-rior and on the coast. In order to do this, I have chosen eight places, some of which lie under the same geographic parallels,and others in the prolongation of the same isothermal line. Ihave compared the temperatures of winter, of summer, and ofthe warmest months; for a summer of uniform heat excites lessthe force of vegetation, than a great heat, preceded by a cold sea-son. The terms of comparison have been along the Atlantic;the coasts of Brittany, (from St Malo and St Brieux to Vannesand Nantes); the sands of Olonne; the Isle of Oleron; theembouchure of the Garonne and Dax, in the department of theLandes; and in the interior, corresponding to the same parallel,Chalons sur Marne, Paris, Chartres, Troyes, Poitiers, andMontauban. Farther south, from 44\( \frac{1}{2} \)° of Lat. the comparisonsbecome incorrect, because France, locked between the Oceanand the Mediterranean, presents, along this last basin, in thefine region of the olives, a system of climate of a particularkind, and very different from that of the western coast.
| Places in the Interior. | Lati-tude. | Mean Temperature | |||
| Ofthe Year. | OfWinter. | OfSummer. | Of theWarmestMonth. | ||
| Fahr. | Fahr. | Fahr. | Fahr. | ||
| Chalons sur Marne, ‒ | 48°.57 | 50°.5 | 36°.1 | 66°.6 | 67°.5 |
| Paris, ‒ ‒ ‒ | 48.50 | 51.1 | 38.7 | 65.3 | 67.5 |
| Chartres, ‒ ‒ | 48.26 | 50.7 | 37.0 | 64.6 | 65.7 |
| Troyes, ‒ ‒ | 48.18 | 52.2 | 38.3 | 67.3 | 68.4 |
| Chinon, ‒ ‒ | 47.26 | 53.4 | 38.7 | 69.1 | 70.2 |
| Poitiers, ‒ ‒ | 46.39 | 54.3 | 39.7 | 67.1 | 69.3 |
| Vienne, ‒ ‒ | 45.31 | 55.0 | 38.7 | 71.6 | 73.4 |
| Montauban, ‒ | 44.01 | 55.6 | 42.6 | 69.3 | 71.4 |
|
|
|||||
| Places on the Coast. | |||||
| St Malo, ‒ ‒ | 48°.39′ | 55°.5 | 42°.4 | 66°.9 | 67°.5 |
| St Brieux, ‒ ‒ | 48.31 | 52.3 | 41.7 | 64.4 | 67.1 |
| Vannes, ‒ ‒ | 47.39 | 51.8 | 39.7 | 64.4 | 65.8 |
| Nantes, ‒ ‒ | 47.13 | 54.7 | 40.5 | 68.5 | 70.5 |
| La Rochelle, ‒ ‒ | 46.14 | 53.1 | 40.3 | 66.6 | 67.1 |
| Oleron, ‒ ‒ | 45.55 | 58.1 | 44.6 | 68.5 | 72.1 |
| Bourdeaux, ‒ ‒ | 44.50 | 56.5 | 42.1 | 70.9 | 71.4 |
| Dax, ‒ ‒ ‒ | 43.52 | 54.1 | 44.4 | 67.3 | 68.9 |
| MeanWinter. | MeanSummer. | ||||
| I. IsothermalLines of | 52°.7 | Coast, ‒ | 40°.6 | 65°.1 | |
| Interior, ‒ | 38.5 | 68.0 | |||
| 54°.7 | Coast, ‒ | 41.4 | 67.3 | ||
| Interior, ‒ | 39.2 | 68.4 | |||
| AnnualTemp. | |||||
| I. Parallels of | 47° to 49° | Coast, | 41°.0 | 66°.7 | 53°.0 |
| Interior, | 37.8 | 66.6 | 51.6 | ||
| 45° to 46° | Coast, | 42.3 | 67.8 | 55.8 | |
| Interior, | 39.2 | 69.3 | 54.7 |
* Young’s Travels in France, vol. ii. p. 195.|29| over the globe, as deducible from the thermometrical variationsof the air, we are far from considering these laws as the onlyones necessary to resolve all the problems of climate. Most ofthe phenomena of nature present two distinct parts, one whichmay be subjected to exact calculation, and another which can-not be reached but through the medium of induction and ana-logy. Having considered the division of heat between winter andsummer on the same isothermal line, we shall now point out thenumerical ratios between the mean temperature of spring andwinter, and between that of the whole year and the warmestmonth. From the parallel of Rome to that of Stockholm, andconsequently between the isothermal lines of 60°.8 and 41°,the difference of the months of April and May is everywhere10°.8 or 12°.6, and all the successive months are those whichpresent the most rapid increase of temperature. But, as innorthern countries, in Sweden, for example, the month ofApril is only 37°.4, the 10°.8 or 12°.6 which the month ofMay adds *, necessarily produces there a much greater ef-fect on the developement of vegetation than in the south of Eu-rope, where the mean temperature of April is from 53°.6 to55°.4. It is from an analogous cause, that in passing from theshade to the sun, either in our climates in winter, or betweenthe tropics on the back of the Cordilleras, we are more affectedby the difference of temperature than in summer and in theplains, though in both cases the thermometrical difference is thesame, for example from 5°.4 to 7°.2. Near the polar circle, theincrease of the vernal heat is not only more sensible, but it ex-tends equally to the month of June. At Drontheim, the tem-peratures of April and May, like those of May and June, differnot 10°.8 or 12°.6, but 14°.4 or 16°.2. In distinguishing upon the same isothermal line the placeswhich approach its concave or convex summits, in the same sys-
* In calculating for Europe, from 46° to 48° of Lat. for ten years the meantemperatures of every ten days, we find, that the decades which succeed one another,differ near the summits of the annual curve only 1°.44, while the differences risein autumn from 3°.6 to 5°.4, and in spring from 5°.4 to 7°.2.—H.|30| tem of climates in the northern and southern regions, we shallfind, 1st, That the increase of the vernal temperature is great,(from 14°.4 or 16°.2, in the space of a month), and equally pro-longed, wherever the division of the annual heat between theseasons is very unequal, as in the north of Europe, and in thetemperate part of the United States. 2dly, That the vernal increase is great, (at least above 9° or10°.8), but little prolonged, in the temperate part of Europe. 3dly, That the increase of the vernal temperature is small,(scarcely 7°.2), and equally prolonged, wherever there is an in-sular climate. 4thly, That in every system of climates, in the zones contain-ed between the same meridians, the vernal increase is smaller,and less equally prolonged, in low than in high latitudes. The isothermal zone from 53°.6 to 55°.4, may serve as an ex-ample for confirming these different modifications of spring. InEastern Asia, near the concave summit, the differences of tem-perature between the four months of March, April, May andJune, are very great, and very equal, (15°.7, 13°.3, and 13°.9).In advancing westward towards Europe, the isothermal linerises again, and in the interior of the country, near the convexsummit, the increase is still greater, but little prolonged; that isto say, that of the four months which succeed one another, thereare only two whose difference rises to 13°: they are 9°.4; 13°.3;4°.1. Farther west, on the coasts, the differences become smalland equal, viz. 3°.6; 6°.5; 5°.6. In crossing the Atlantic, weapproach the western concave summit of the isothermal line of53°.6. The increase of vernal temperature shews itself anew,and almost as great, and as much prolonged, as near the Arcticconcave summit. The differences of the four months are 10°.4;13°.9; and 10°.8. In the curve of annual temperature, thespring and autumn mark the transitions from the minimum andthe maximum. The increments are naturally slower near the sum-mits than in the intermediate part of the curve. Here they aregreater, and of longer continuance, in proportion to the diffe-rence of the extreme ordinates. The autumnal decrease of tem-perature is less rapid than the vernal increase, because the sur- |31| face of the earth acquires the maximum of heat slower than theatmosphere, and because, in spite of the serenity of the air whichprevails in autumn, the earth loses slowly, by radiation, the heatwhich it has acquired. The following Table will shew howuniform the laws are which I have just established.
| Names of Places. | Lati-tude. | March. | April. | May. | June. | Differences of Tem-perature of the FourMonths. | MeanTemp. ofthe Year. | |||
| I. Group,—Concave Summits in America. | ||||||||||
| Natchez, ‒ ‒ ‒ | 31° 28′ | 57°.9 | 66°.2 | 72°.7 | 79°.5 | 8°.3 | 6°.1 | 7°.2 | 64°.8 | |
| Williamsburg, ‒ ‒ | 37 18 | 46.4 | 61.2 | 66.6 | 77.7 | 14.8 | 5.4 | 11.2 | 58.1 | |
| Cincinnati, ‒ ‒ | 39 0 | 43.7 | 57.4 | 61.2 | 70.9 | 13.7 | 3.6 | 9.7 | 53.8 | |
| Philadelphia, ‒ ‒ | 39 56 | 44.1 | 53.6 | 62.1 | 72.3 | 9.5 | 8.5 | 10.3 | 53.6 | |
| New York, ‒ ‒ | 40 40 | 38.7 | 49.1 | 65.8 | 80.2 | 10.4 | 16.7 | 14.4 | 53.8 | |
| Cambridge, ‒ ‒ | 42 25 | 34.5 | 45.5 | 56.8 | 70.2 | 11.0 | 11.3 | 13.3 | 50.4 | |
| Quebec, ‒ ‒ ‒ | 46 47 | 23.0 | 39.6 | 54.7 | 63.9 | 16.6 | 15.1 | 41.2 | 41.7 | |
| Nain, ‒ ‒ ‒ | 57 0 | 6.8 | 27.5 | 37.0 | 43.3 | 20.7 | 9.5 | 8.1 | 26.4 | |
| II. Group,—Convex Summits in Europe. | ||||||||||
| 1. | Continental Climate: | |||||||||
| Rome, ‒ ‒ ‒ | 41 53 | 50.4 | 55.4 | 66.9 | 72.3 | 5.0 | 11.5 | 5.4 | 60.4 | |
| Milan, ‒ ‒ ‒ | 45 28 | 47.8 | 51.1 | 65.1 | 70.5 | 7.7 | 9.5 | 5.4 | 55.8 | |
| Geneva, ‒ ‒ ‒ | 46 12 | 39.6 | 45.5 | 58.1 | 62.2 | 6.1 | 12.4 | 4.1 | 49.3 | |
| Buda, ‒ ‒ ‒ | 47 29 | 38.3 | 49.1 | 64.8 | 68.4 | 10.8 | 15.7 | 3.6 | 51.1 | |
| Paris, ‒ ‒ ‒ | 48 50 | 42.3 | 48.2 | 60.1 | 64.4 | 8.5 | 11.9 | 4.3 | 51.1 | |
| Gottingen, ‒ ‒ | 51 32 | 34.2 | 44.2 | 57.7 | 62.2 | 10.1 | 13.5 | 4.5 | 46.9 | |
| Upsal, ‒ ‒ ‒ | 59 51 | 29.5 | 39.7 | 48.7 | 57.9 | 10.3 | 9.0 | 9.2 | 41.9 | |
| Petersburg, ‒ ‒ | 59 56 | 27.5 | 37.0 | 50.2 | 59.4 | 9.5 | 13.1 | 9.2 | 38.8 | |
| Umeo, ‒ ‒ ‒ | 63 50 | 23.0 | 34.2 | 43.7 | 55.0 | 11.2 | 9.5 | 11.3 | 33.3 | |
| Uleo, ‒ ‒ ‒ | 65 0 | 14.0 | 26.2 | 41.0 | 55.0 | 12.2 | 14.8 | 14.0 | 33.1 | |
| Enontekies, ‒ ‒ | 68 30 | 11.5 | 26.6 | 36.5 | 49.5 | 15.1 | 9.9 | 13.0 | 27.0 | |
| 2. | Climate of the Coast: | |||||||||
| Nantes, ‒ ‒ ‒ | 47 13 | 50.0 | 53.6 | 60.1 | 65.7 | 3.6 | 6.5 | 5.6 | 54.7 | |
| London, ‒ ‒ ‒ | 51 30 | 44.2 | 49.8 | 56.5 | 63.1 | 5.6 | 6.7 | 6.7 | 51.6 | |
| Dublin, ‒ ‒ ‒ | 53 21 | 41.9 | 45.3 | 51.8 | 55.6 | 3.4 | 6.5 | 4.0 | 48.4 | |
| Edinburgh, ‒ ‒ | 55 57 | 41.4 | 47.3 | 50.5 | 57.2 | 5.8 | 3.2 | 6.7 | 47.8 | |
| North Cape, ‒ ‒ | 71 0 | 25.0 | 30.0 | 34.0 | 40.1 | 5.2 | 4.0 | 6.1 | 32.0 | |
| III. Group,—Concave Summit of Asia. | ||||||||||
| Pekin, ‒ ‒ ‒ | 39 54 | 41.4 | 57.0 | 70.3 | 84.2 | 15.7 | 13.3 | 13.9 | 54.9 | |
- 41°.9, the Peach-tree (Amygdalus Persica) flowers.
- 46°.8, the Plum-tree (Prunus domestica) flowers.
- 51°.8, the Birch-tree * (Betula alba) pushes out its leaves.
* Cotte, Meteorologie, p. 448.—Wahlenberg, Flor. Lap. Pl. 51.† Playfair, Edin. Trans, vol. v. p. 202.— Wahlenberg in Gilbert’s Annalen, tom. xli. p. 282.|33|
| Lines of Equal Heat. | Names ofPlaces. | Latitude. | MeanTemp.of theYear. | Sum of theMean Temp.of the Monthsthat reach51°.8. | Numberof thoseMonths. | Mean Tem-perat. of thedays whichreach 51°.8. | Mean Tem-perature ofthe warm-est Months. | Observations. |
| Isothermal Line of 59°.0, | Rome, ‒ | 41° 53′ | 60°.4 | 585° | 9 | 64°.8 | 77°.0 | Basin of the Mediterranean. |
| Nismes, | 43 50 | 60.3 | 593 | 9 | 65.8 | 78.3 | Idem. | |
| Isothermal Line of 53°.6, | Pekin, ‒ | 39 54 | 54.9 | 499 | 7 | 71.2 | 84.2 | Eastern concave summit. |
| Poitiers, | 46 34 | 54.3 | 426 | 7 | 60.8 | 69.3 | Convex summit. | |
| Nantes, | 47 13 | 54.7 | 438 | 7 | 62.6 | 69.8 | Idem, coasts. | |
| St Malo, | 48 39 | 53.8 | 431 | 7 | 61.5 | 68.4 | Idem. | |
| Philadelphia, | 39 56 | 53.4 | 463 | 7 | 66.2 | 77.0 | Western concave summit. | |
| Cincinnati, | 39 6 | 53.8 | 458 | 7 | 65.5 | 74.3 | Idem. | |
| Isothermal Line of 50°.0, | London, | 51 30 | 51.8 | 364 | 6 | 60.6 | 66.6 | Insular climate. |
| Paris, ‒ | 48 50 | 51.1 | 381 | 6 | 63.5 | 69.8 | Near the coasts. | |
| Buda, ‒ | 47 29 | 51.1 | 323 | 5 | 64.6 | 72.0 | Interior. | |
| Isothermal Line of 48°.2, | Geneva, | 46 12 | 49.3 | 311 | 5 | 62.2 | 66.6 | Interior. |
| Dublin, | 53 21 | 48.7 | 282 | 5 | 56.5 | 60.8 | Climate of the coasts. | |
| Edinburgh, | 55 57 | 47.8 | 279 | 5 | 55.8 | 59.4 | Idem. | |
| Isothermal Line of 41°.0, | Upsal, ‒ | 59 51 | 41.9 | 229 | 4 | 57.2 | 61.9 | Convex summit. |
| Quebec, | 46 47 | 41.7 | 318 | 5 | 63.7 | 73.4 | Western concave summit. | |
| Isothermal Line of 32°.0, | Petersburgh, | 59 56 | 38.8 | 236 | 4 | 59.0 | 65.7 | East of Europe. |
| Umeo, ‒ | 53 50 | 33.3 | 118 | 2 | 59.0 | 62.6 | E. Coast of Gulf of Bothnia. | |
| North Cape, | 71 0 | 32.0 | 0 | 0 | 0 | 46.6 | Interior climate. | |
| Enontekies, | 68 30 | 27.0 | 116 | 2 | 58.1 | 59.5 | Continental climate. |
| Names ofPlaces. | Mean Temperature | ||
| Of theYear. | Of Oc-tober. | OfApril. | |
| Cairo, ‒ | 72°.3 | 72°.3 | 77°.9 |
| Algiers, ‒ | 69.8 | 72.1 | 62.6 |
| Natchez, | 65.0 | 68.4 | 66.4 |
| Rome, ‒ | 60.4 | 62.1 | 55.4 |
| Milan, | 55.8 | 58.1 | 55.6 |
| Cincinnati, | 53.6 | 54.9 | 56.8 |
| Philadelphia, | 53.4 | 54.0 | 53.6 |
| New York, | 53.8 | 54.5 | 49.1 |
| Pekin, ‒ | 54.7 | 55.4 | 57.0 |
| Buda, ‒ | 51.1 | 52.3 | 49.1 |
| London, ‒ | 51.8 | 52.3 | 49.8 |
| Paris, ‒ | 51.1 | 51.3 | 48.2 |
| Geneva, ‒ | 49.3 | 49.3 | 45.7 |
| Dublin, ‒ | 48.6 | 48.7 | 45.3 |
| Edinburgh, | 47.8 | 48.2 | 46.9 |
| Names ofPlaces. | Mean Temperature | ||
| Of theYear. | Of Oc-tober. | OfApril. | |
| Gottingen, | 46°.9 | 47°.1 | 44°.4 |
| Franeker, | 52.3 | 54.9 | 50.0 |
| Copenhagen, | 45.7 | 48.7 | 41.0 |
| Stockholm, | 42.3 | 42.4 | 38.5 |
| Christiania, | 42.6 | 39.2 | 42.6 |
| Upsal, ‒ | 41.7 | 43.3 | 39.7 |
| Quebec, | 41.9 | 42.8 | 39.6 |
| Petersburgh, | 38.8 | 39.0 | 37.0 |
| Abo, ‒ | 41.4 | 4.0 | 40.8 |
| Drontheim, | 39.9 | 39.2 | 34.3 |
| Uleo, ‒ | 33.1 | 37.9 | 34.2 |
| Umeo, ‒ | 33.3 | 37.8 | 34.0 |
| North Cape, | 32.0 | 32.0 | 30.2 |
| Enontekies, | 27.0 | 27.5 | 26.6 |
| Nain, ‒ | 26.4 | 33.1 | 27.5 |
| Mean | Mean | ||
| Years. | Temp. | Years. | Temp. |
| 1796, | 49°.3 | 1806, | 51°.4 |
| 1797, | 50.5 | 1807, | 49.3 |
| 1798, | 50.0 | 1808, | 46.9 |
| 1799, | 48.7 | 1809, | 48.9 |
| 1800, | 50.5 | 1810, | 51.1 |
| 1801, | 51.1 | 1811, | 51.6 |
| 1802, | 50.9 | 1812, | 47.8 |
| 1803, | 50.4 | 1813, | 48.6 |
| 1804, | 51.1 | 1814, | 48.2 |
| 1805, | 47.8 | 1815, | 50.0 |
| Mean of 20 Years, | 49°.67 | ||
| Observations ofM. Bouvard. | Mean Temperature | |||||
| Of theYear. | Of Win-ter. | Of Sum-mer. | Of Ja-nuary. | Of Au-gust. | Of Oc-tober. | |
| Paris, 1803, ‒ | 51°.1 | 36°.7 | 67°.6 | 34°.3 | 67°.6 | 50°.5 |
| 1804, ‒ | 52.0 | 41.0 | 65.5 | 43.9 | 64.6 | 52.7 |
| 1805, ‒ | 49.5 | 36.0 | 63.1 | 34.9 | 64.8 | 49.3 |
| 1806, ‒ | 53.4 | 40.6 | 65.3 | 43.0 | 64.6 | 51.8 |
| 1807, ‒ | 51.4 | 42.3 | 67.8 | 36.1 | 70.5 | 54.3 |
| 1808, ‒ | 50.5 | 36.7 | 66.2 | 36.3 | 66.6 | 48.2 |
| 1809, ‒ | 50.9 | 40.5 | 62.4 | 40.8 | 64.2 | 49.6 |
| 1810, ‒ | 50.9 | 36.5 | 63.3 | 30.6 | 63.7 | 52.9 |
| 1811, ‒ | 52.7 | 39.2 | 65.1 | 26.6 | 63.7 | 57.6 |
| 1812, ‒ | 49.8 | 39.6 | 63.1 | 34.7 | 64.2 | 51.1 |
| 1813, ‒ | 49.8 | 36.1 | 61.7 | 32.5 | 62.6 | 53.1 |
| Mean of these 11 years, | 51°.1 | 38°.7 | 64°.0 | 36°.6 | 65°.1 | 51°.9 |
| Years. | Mean Tempof Summers. | |
| 1803, | ‒ | 67°.3 |
| 1804, | ‒ | 65.0 |
| 1805, | ‒ | 62.2 |
| 1806, | 65.7 | |
| 1807, | ‒ | 68.2 |
| 1808, | ‒ | 62.9 |
| 1809, | ‒ | 63.0 |
| Mean of seven years, | 64°.9 | |
| Years. | Paris. | Geneva. | Paris. | Geneva. | Paris. | Geneva. | ||||||
| MeanAnnualTempe-rature. | DifferencebetweenMean Ann.Temp. andthat for 12years,51°.1 | MeanAnnualTempe-rature. | DifferencebetweenMean An.Temp. andthat of 12years,49°.6. | MeanTempe-rature ofWinter. | Differencewith themean Win-ter Tempe-rature of12 years,38°.7. | MeanTempe-rature ofWinter. | Differencewith theMean Win-ter Tempe-rature of12 years,34°.9. | MeanTempe-rature ofSummer. | Differencewith theMean Tem-rature ofSummer for12 years,64°.6. | MeanTempe-rature ofSummer. | Differencewith theMean Tem-perature ofSummer for12 years,64°.9. | |
| 1803, | 51°.1 | 0 | 50°.4 | + 0.8 | 36°.7 | — 2.0 | 32°.2 | — 2°.7 | 67°.6 | + 3°.0 | 67°.6 | + 2.7 |
| 1804, | 52.0 | + 0.9 | 51.1 | + 1.5 | 41.0 | + 2.3 | 38.3 | + 3.4 | 65.5 | + 0.9 | 66.2 | + 1.3 |
| 1805, | 49.5 | — 1.6 | 47.8 | — 1.8 | 36.0 | — 2.7 | 33.8 | — 1.1 | 63.1 | — 1.5 | 63.0 | — 1.9 |
| 1806, | 53.4 | + 2.3 | 51.4 | + 1.8 | 40.6 | + 1.9 | 38.5 | + 3.6 | 65.3 | + 0.7 | 64.6 | — 0.3 |
| 1807, | 51.4 | + 0.3 | 49.3 | — 0.3 | 42.3 | + 3.6 | 35.8 | + 0.9 | 67.8 | + 3.2 | 68.2 | + 3.3 |
| 1808, | 50.5 | — 0.6 | 46.8 | — 2.8 | 36.7 | — 2.0 | 33.8 | — 1.1 | 66.2 | + 1.6 | 63.5 | — 1.4 |
| 1809, | 50.9 | — 0.2 | 48.7 | — 0.9 | 40.5 | + 1.8 | 35.1 | + 0.2 | 62.4 | — 2.2 | 63.1 | — 1.8 |
| 1810, | 50.9 | — 0.2 | 51.1 | + 1.5 | 36.5 | — 2.2 | 63.3 | — 1.3 | ||||
| 1811, | 52.7 | + 1.6 | 51.8 | + 2.2 | 39.2 | + 0.5 | 65.1 | + 0.5 | ||||
| 1812, | 49.8 | — 1.3 | 47.8 | — 1.8 | 39.6 | + 0.9 | 63.1 | — 1.5 | ||||
| 1813, | 49.8 | — 1.3 | 48.6 | + 1.0 | 36.1 | — 2.6 | 61.7 | — 2.9 | ||||
On Isothermal Lines, and the Distribution of Heatover the Globe. By Baron Alexander de Humboldt. (Continued from Vol. IV. p. 37.)
* Theorie de la Terre, tom. i. p. 312.—Mémoires de l’Acad. 1765, p. 174.† De Distributione Caloris, 1761.‡ Estimate, &c. p. 60.—Irish Trans. vol. viii. p. 423.—Le Gentil, Voyagedans l’Inde, vol. i. p. 73.║ Mairan, Mem. Acad. 1765, p. 166.—Lambert, Pyrometrie, p. 310.Prevost, De la Chaleur Rayonnante, 1809, p. 329. & 367. § 280,—306.|263| water, the pyramidal extremities of the continents have there anirregular climate. Summers of a very low temperature are suc-ceeded, as far as 50° of south latitude, by winters far from ri-gorous. The vegetable forms also of the torrid zone, the ar-borescent ferns, and the orchideous parasites, advance towards38° and 42° of S. Latitude. The small quantity of land * in the southern hemispheres, contributes not only to equalise theseasons, but also to diminish absolutely the annual temperatureof that part of the globe. This cause is, I think, much moreactive than that of the small eccentricity of the earth’s orbit.The continents during summer radiate more heat than the seas,and the ascending current which carries the air of the equinoc-tial and temperate zones towards the circumpolar regions, actsless in the southern than in the northern hemisphere. Thatcap of ice which surrounds the pole to the 71st and 68th degreeof south latitude, advances more towards the equator, wheneverit meets a free sea; that is, wherever the pyramidal extremitiesof the great continents are not opposite to it. There is reasonto believe, that this want of dry land would produce an ef-fect still more sensible, if the division of the continents was asunequal in the equinoctial as in the temperate zones †. Theory and experience prove, that the difference of tempera-ture between the two hemispheres, cannot be great near thelimit which separates them ‡. Le Gentil had already observed,that the climate of Pondicherry is not warmer than that of Ma-dagascar at the Bay of Antongel in 12° of S. Lat. Under theparallels of 20 the Isle of France has the same annual tempera-ture, viz. 80°.1, as Jamaica and St Domingo. The IndianSea between the east coasts of Africa, the Isles of Sonde andNew Holland, form a kind of gulf which is shut up to the northby Arabia and Hindostan. The isothermal lines there appearto go back to the South Pole; for farther to the west in the opensea between Africa and the New World, the cold of the south-ern hemisphere already causes itself to be felt from the 22d de-gree, on account of its insulated mountains and particular loca-
* The dry lands in the two hemispheres are in the ratio of 3 to 1.† The dry lands between the tropics, are in the two hemispheres as 5 to 4,and without the tropies as 13 to 1.‡ Prevost, p. 343.|264| lities. 1 shall not mention the island of St Helena, Lat. 15°55′ whose mean temperature, according to the observations of M.Beatson, at the sea side, does not exceed 71°6 or 73°4. It isthe eastern coast of America, which, in the observations of a Por-tuguese astronomer, M. Benito Sanchez Dorta *, present us withthe S. Lat. of 22° 54′, almost at the limit of the equinoctialregion with a plan, of which we know the climate by more than3500 thermometrical and barometrical observations made everyyear, to ascertain the horary variations in the heat and pressureof the air. The mean temperature of Rio Janeiro is only 74°.3,whilst, notwithstanding the north winds which bring the coldair of Canada during winter into the Gulf of Mexico, the meantemperatures of Vera Cruz, (Lat. 19° 11′,) and of the Havannah,(Lat. 23° 10′,) are 77°.9. The differences of the two hemis-pheres become more sensible in the warmest months.
| Rio Janeiro. | Havannah. | ||
| Mean Temp. | Mean Temp. | ||
| June, | 68°.0 | December, | 71°.8 |
| July, | 70 2 | January, | 70 2 |
| January, | 79 2 | July, | 83 3 |
| February, | 80 6 | August, | 83 8 |
* Mem. de l’Acad. de Lisbonne, tome ii. p. 348. 369.†
| Latitude. | Mean Temp. | |
| † Natchez, | 31° 28′, | 64°.8 |
| Cincinnati, | 39 06, | 53.8. |
*
| Latitude. | Mean Temp. | |
| Cairo, | 30° 2′ | 72°.3 |
| Funchal, | —— 32 37 | 68 5 |
| Algiers, | —— 36 48 | 70 0 |
* It is the more surprising to find in the Island of Georgia snow on the banksof the ocean, because 2° 39′ nearer the Equator at the Malouine Isles, the meantemperature of the summers is 53°.1, or 9° greater than at the point in ourhemisphere in 71° of Lat. where the limit of perpetual snow exists at 2296 feetof absolute elevation. But we must recollect, 1st, That the Malouine Isles arenear a continent which is heated in summer; 2d, That Georgia is covered withmountains, and is placed not only in a sea open to the north, but under the influ-ence of the perennial ices of Sandwich Land; and, 3dly, That in Lapland, 20° ofLat. produce in certain local circumstances 10°.8 of difference in the tempera-tures of the summers.† Baron Von Buch’s Travels in Lapland, vol. ii. p. 393,—420.|267| earth’s orbit, than of the unequal division of the continents, de-termines * the limit between the N. E. and S. E. Trade Winds.But as this limit is much more to the north of the Equator inthe Atlantic Ocean, than in the South Sea, we may concludethat, in a region between 130° and 150° of W. Long. the dif-ference of temperature between the two hemispheres, is less greatthan farther to the east in 20° or 50° of longitude. It is in-deed under this region in the Great Ocean, that, as far as theparallel of 60°, the two hemispheres are equally covered withwater, and equally destitute of dry land, which, radiating theheat during summer, sends the warm air towards the poles. Theline which limits the N. E. and S. E. Trade Winds, approachesthe Equator, whereas the temperature of the hemispheres is dif-ferent; and if, without diminishing the cold of the southern at-mosphere, we could increase the inflexion of the isothermal linesin the system of transatlantic climates, we should meet the S. E.winds in 20° and 50° of W. Long. to the north, and in 130°and 150° of W. Long. to the south of the Equator †. The low strata of the atmosphere which rest upon the aque-ous surface of the globe, receive the influence of the tempera-ture of the waters. The sea radiates less absolute heat thancontinents; it cools the air upon the sea, by the effect of eva-poration; it sends the particles of water cooled and heavier to-wards the bottom; and it is heated again, or cooled, by the cur-rents directed from the Equator to the Poles, or by the mixtureof the superior and inferior strata on the sides of banks. It is from these causes combined, that, between the tropics,and perhaps as far as 30° of Lat., the mean temperatures of theair next the sea, are 3°.6 or 5°.4 lower than that of the conti-nental air. Under high latitudes, and in climates where theatmosphere is coolest in winter, much below the freezing point,the isothermal lines rise again towards the Poles, or becomeconvex when the continents pass below the seas ‡. With respect to the temperature of the ocean, we must dis-tinguish between four very different phenomena. 1st, The tem-
* Prevost, Journ. de Phys. tom. xxxviii. p. 369.—Irish Trans. vol. viii, p. 374.† Humboldt’s Relat. Histor. tom. i. p. 225, 237.‡ Id. p. 67, 230. 242.|268| perature of the water at the surface corresponding to differentlatitudes, the ocean being considered at rest, and destitute ofshallows and currents. 2d, The decrease of heat in the super-imposed strata of water. 3d, The effect of billows on the tem-perature of the surface water. 4th, The temperature of cur-rents, which impell with an acquired velocity, the waters of ourzone across the immoveable waters of another zone. The re-gion of warmest waters no more coincides with the Equator, thanthe region in which the waters reach their maximum of saltness.In passing from one hemisphere to another, we find the warmestwaters between 5° 45′ of N. Lat., and 6° 15′ of S. Lat. Per-rins found their temperature to be 82°.3; Quevedo 83°.5;Churruca 83°.7, and Rodman 83°.8. I have found them inthe South Sea to the east of the Galapagos Isles 84°.7. The va-riations and the mean result do not extend beyond 1°.3. Itis very remarkable that in the parallel of warmest waters, thetemperature of the surface of the sea is from 3°.6 to 5°.4higher than that of the superincumbent air. Does this differencearise from the motion of the cooled particles towards the bot-tom, or the absorption of light, which is not sufficiently compen-sated by the free emission of the radiant coloric. As we ad-vance from the Equator to the Torrid Zone, the influence ofthe seasons on the temperature of the surface of the sea be-comes very sensible; but as a great mass of water follows veryslowly the changes in the temperature of the air, the means ofthe months do not correspond at the same epochs in the oceanand in the air. Besides, the extent of the variations is less inthe water than in the atmosphere, because the increase or de-crease in the heat of the sea takes place in a medium of varia-ble temperature, so that the minimum and the maximum of theheat which the water reaches, are modified by the atmospheri-cal temperature of the months which follow the coldest of thewarmest months of the year. It is from an analogous cause,that in springs which have a variable temperature, for example,near Upsal *, the extent of the variations of temperature is only19°.8, while the same extent in the air from the month of Janu-ary to August, is 39°.6. In the parallel of the Canary Islands,
* Gilbert’s Annalen, 1812, p. 129.|269| Baron Von Buch found the minimum of the temperature of thewater to be 68°, and the maximum 74°.8. The temperatureof the air in the warmest of the coldest months, is, in that quar-ter, from 64°.4 to 75°.2. In advancing towards the north,we find still greater differences of winter temperature betweenthe surface of the sea and the superincumbent air. The cooledparticles of water descend till their temperature reaches 39°.2;and hence in 46° and 50° of Lat. in the part of the Atlanticwhich is near Europe, the maximum and minimum of heat are In the water at its surface, 68°.0 and 41°.9 In the air from the mean of warmest and coldest months, 66.2 and 35.6 The excess in the mean temperature of the water over that ofthe air, attains its maximum beyond the polar circle, where thesea does not wholly freeze. The atmosphere is cooled to such adegree in these seas, (from 63° to 70° of Lat., and 0° of Long.)that the mean temperature of several months of winter descendon the continents to 14° and 10°.4, and on the coasts to 23°and 21°.2, while the temperature of the surface of the sea isnot below 32° or 30°.2. If it is true, that even in those highlatitudes the bottom of the sea contains strata of water which,at the maximum of their specific gravity, have 39°.2 or 41° ofheat, we may suppose that the water at the bottom contributesto diminish the cooling at the surface. These circumstanceshave a great influence on the mildness of countries in continentsseparated from the Pole by an extensive sea. Hitherto we have attended to the distribution of heat on thesurface of the globe at the level of the sea. It only remains forus to consider the variations of temperature in the higher re-gions of the atmosphere, and in the interior of the earth. The decrease of heat in the atmosphere, depends on severalcauses, the principle of which, according, to Laplace and Les-lie *, is the property of the air to increase its capacity for heat byits rarefaction. If the globe was not surrounded by a mixtureof elastic and aëriform fluids, it would not be sensibly colder atthe height of 8747 yards than at the level of the sea. As each
* Essay on Heat and Moisture, p. 11.; and Geometry, p. 495.|270| part of the globe radiates in every direction, the interior of aspherical envelope which would rest on the top of the highestmountains, would receive the same quantity of radiant heat asthe lower strata of the atmosphere. The heat, it is true, willbe spread over a surface a little greater; but the difference oftemperature will be insensible, since the radius of the sphericalenvelope will be to that of the earth as 1.001 to 1. Considering the earth as surrounded with an atmosphericalfluid, it is obvious, that the air heated at its surface will ascend,dilate itself, and be cooled, either by dilatation, or, by a morefree radiation across the other strata that are equally rarified.These are the ascending and descending currents, which keepup the decreasing temperature of the atmosphere *. The cold of mountains is the simultaneous effect, 1st, Of thegreater or less vertical distance of the strata of air at the surfaceof the plains and of the ocean. 2d, Of the extinction of light,which diminishes with the density of the superincumbent strataof air †; and, 3d, Of the emission of radiant heat, which is fa-voured by air very dry ‡, very cold, and very clear. The meantemperature of our present plains would be lowered, if the seasshould experience a considerable diminution. The plains ofcontinents would then become plateaux, and the air which rest-ed on them would be cooled by the circumjacent strata of air,which, at the same level, would receive but a small portion ofthe heat emitted from the dry bottom of the seas. The following Table contains the results of observationswhich I have made near the Equator, on the Andes of Quito,and towards the northern extremity of the torrid zone, in theCordilleras of Mexico. These results are true means, given ei-ther by stationary observations made during several years, orby insulated observations. In these last, we have taken intoaccount the hour of the day,—the distance of the solstices,—thedirection of the wind,—and the reflection from the plains.
* Essay on Heat and Moisture, p. 11.; and Geometry, p. 495.† Humboldt on Refraction below 10°, Observ. Astron. tom. i. p. 126.‡ Wells on Dew, p. 50.|271|
| Height abovethe Level ofthe Sea. | Cordilleras of the Andes. From 10° of North Lat.to 10° of South Lat. | Mountains of Mexico. From 17° of North Lat.to 21° of North Lat. | ||||||||||||||||||||||||||||||||||||||||
| MeanTemp.of theYear. | Examples, which may serve as aType. | MeanTemp.of theYear. | Examples, which may serve as aType. | |||||||||||||||||||||||||||||||||||||||
| 0 Toises.0 Feet.(Comparativeheights in Europehave been addedfor every 1000metres.) | Fahr.81°.5 |
|
78°.80 |
|
||||||||||||||||||||||||||||||||||||||
| 500 Toises.3197 Feet. Vesuvius 3870feet. | 71°.24 |
|
67°.64 |
|
||||||||||||||||||||||||||||||||||||||
| 1000 Toises.6394 Feet. Hospice of St Go-thard, 6806 feet. | 64°.4 |
|
64°.4 |
|
||||||||||||||||||||||||||||||||||||||
| 1500 Toises.9591 Feet. Canigou, 9118feet. | 57°.74 |
|
57°.2 |
|
||||||||||||||||||||||||||||||||||||||
| 2000 Toises.12,789 Feet. Peak of Teneriffe, 12,169 feet. | 44°.6 |
|
45°.5 |
|
||||||||||||||||||||||||||||||||||||||
| 2500 Toises.15,985 Feet. Mont Blanc, 15,662 feet. | 37°.7 |
|
33°.8 |
|
||||||||||||||||||||||||||||||||||||||
| Alt. inFeet. | MeanTemp. | |
| Coasts of Cumana, | 0 | 80°.6 |
| 82.4 | ||
| Tomependa, Amazons R. | 1279 | 78.44 |
| Tocayma, ‒ ‒ | 1581 | 81.5 |
| Antioquia, ‒ ‒ | 1666 | 77.00 |
| Neiva, ‒ ‒ | 1702 | 77.00 |
| Caraccas, ‒ ‒ | 2906 | 69.44 |
| Caripe, ‒ ‒ | 2959 | 65.3 |
| Carthago, ‒ ‒ | 3149 | 74.84 |
| La Plata, ‒ ‒ | 3437 | 74.66 |
| Guaduas, ‒ ‒ | 3772 | 67.46 |
| La Meya, ‒ ‒ | 4225 | 72.50 |
| Medellin, ‒ ‒ | 4858 | 68.9 |
| Estrella, ‒ ‒ | 5645 | 65.84 |
| Popayan, ‒ ‒ | 5815 | 65.66 |
| Loxa, ‒ ‒ | 6855 | 64.4 |
| Almaguer, ‒ ‒ | 7413 | 62.6 |
| Pamplona, ‒ | 8016 | 61.16 |
| Alt. inFeet. | MeanTemp. | |
| Alausi, ‒ ‒ | 7970 | 59°.00 |
| Pasto, ‒ ‒ | 8308 | 58.28 |
| Santa Rosa, ‒ | 8459 | 57.74 |
| Cuenca, ‒ ‒ | 8633 | 60.08 |
| Santa Fé de Bogota, | 8721 | 57.74 |
| Hambato, ‒ ‒ | 8849 | 60.44 |
| Caxamarca, ‒ | 9381 | 60.80 |
| Llactacunga, ‒ | 9473 | 59.00 |
| Riobamba Nuevo, | 9482 | 61.16 |
| Tunja, ‒ ‒ | 9522 | 56.66 |
| Quito, ‒ ‒ | 9538 | 57.92 |
| Malbasa, ‒ ‒ | 9971 | 54.50 |
| Plateau de los Pastos, | 10099 | 54.50 |
| Les Paramos, ‒ | 11480 | 47.30 |
| At the Inferior Li-mit of Perpetualtual Snow, | 15744 | 34.88 |
* I have used the mean temperature and barometrical measurements publishedat Santa Fé de Bogota by MM. Caldas and Restrepo in the Semanario del N. R. deGranada, tom. i. p. 273.; tom. i. p. 93.—341.|273| cular climates, modified by the radiation of the plateaus onwhich they stand,—upon the slope of the ground,—the naked-ness of the soil,—the humidity of the forests,—and the currentswhich descend from the neighbouring summits. Without knowing the localities themselves, the effect of dis-turbing causes will be readily seen, by comparing in the pre-ceding Table the mean temperatures which correspond to thesame elevations; and the discussion of these observations wouldprove, also, that the extent of the variations is much less than isgenerally believed. If we examine thirty-two temperatures, uponthe hypothesis that a degree of cooling corresponds to an altitudeof 200 metres (656 feet), we shall deduce the temperature of theplains (from 30°.6 to 82°.4) twenty-six times from that of elevatedplaces. For the other six deductions, the temperatures differ on-ly about 3°.6; and the errors of observation are here combinedwith the effects of localities. The air which rests on the plains ofthe Andes mixes itself with the great mass of the free atmosphere,in which there prevails under the torrid zone a surprising stabi-lity of temperature. However enormous be the mass of theCordilleras, it acts but feebly on the strata of air which are un-ceasingly renewed. On the other hand, if the plains are heatedduring the day, they radiate as much during the night; for itis principally on the plains elevated 8856 feet above the sea,that the sky is most clear and uniformly serene. At Peru, forexample, the magnificent plateau of Caxamarca, in which thewheat yields the eighteenth, and barley the sixtieth grain, hasan extent of more than twelve square leagues: it is smooth likethe bottom of a lake, and sheltered by a circular wall of moun-tains free from snow. Its mean temperature is 60°.8, yet thewheat is often frozen during the night; and in a season wherethe thermometer fell before sunrise to 46°.4, I have seen it risein the day to 77° in the shade. In the vast plains of Bogota,which are 656 feet less elevated than that of Caxamarca, themean temperature, as established by the fine observations ofMutis, is scarcely 57°.74. In comparing towns situated on elevated plains with thosewhich are placed on the declivity of mountains, I have found forthe first an augmentation of temperature, which, on account of the |274| nocturnal radiation, does not exceed from 2°.7 to 4°.14. Thisaugmentation is a little greater in the lower regions of theAndes, in those large valleys whose smooth bottoms reach theheight of from 1312 to 1640 feet, principally in the valley ofLa Madaleine, between Neiva and Honda. It is singular tofind in the middle of mountains heats which equal those of theplains, and which are more insupportable, as the air of the val-leys is almost never agitated by the winds. If we compare,however, the mean temperatures of these same places with thoseof the strata of the true atmosphere, or on the declivity of moun-tains, we shall find them only from 3°.6 to 5°.4. On these grounds, we may place some confidence on the fourresults which we have deduced from such a great number of ob-servations, for the perpendicular heights of 1000, 2000, 3000,and 4000 metres. I have confined myself to a simple arithme-tical mean, and to the fortuitous compensation of irregularities;for I could not have avoided employing an hypothesis on thedecrease of heat, if I had wished to reduce to a standardheight those heights which approach it the most. I have addedthe observations with which an intimate knowledge of localitieshas furnished me.
| 1. For 1000 Metres (3280 feet) of Elevation. | Alt. inFeet. | Temp.Fahr. |
| Convent of Caripe, (thick and damp forests), ‒ | 2959 | 65°.3 |
| Caraccas, (a foggy sky, valley of small extent,) ‒ | 2906 | 69.44 |
| La Plata, (very warm, valley communicating with that of L’AltoMagdalena,) ‒ ‒ ‒ ‒ | 3437 | 74.66 |
| Carthago, (very warm valley of Cauca), ‒ ‒ | 3149 | 74.84 |
| 2. For 2000 Metres (6560 feet) of Elevation. | ||
| Loxa, (a plateau of small extent), ‒ ‒ | 6855 | 64.4 |
| Almaguer, declivity covered with very thick vegetation), ‒ | 7413 | 62.6 |
| Popayan, (small plateau, a little elevated above the valley of Cau-ca,) ‒ ‒ ‒ ‒ ‒ | 5815 | 65.66 |
| 3. For 3000 Metres (9840 feet) of Elevation. | ||
| Caxamarca, (very extensive plateau, sky serene,) ‒ | 9381 | 60.80 |
| Quito, (at the foot of Pinchincha, a narrow valley,) ‒ | 9538 | 57.92 |
| Tunja, (mountains of New Grenada), ‒ ‒ | 9522 | 56.66 |
| Malvasa, (elevated plains, cooled by the snows of the volcano ofPuracé,) ‒ ‒ ‒ ‒ | 9971 | 54.50 |
| Los Pastos, (very cold plateau, from which rise snow covered sum-mits,) ‒ ‒ ‒ ‒ ‒ | 10099 | 54.50 |
| Llactacunga, (temperate valley), ‒ ‒ | 9473 | 59.0 |
| Riobamba Nuevo, (arid plains of Tupia, covered with pumice-stone,) | 9482 | 61.16 |
* Elevations of 400 metres (1312 feet) appear to have a very sensible influenceon the mean temperature, even when great portions of countries rise progressively.In order to establish this point, I have examined the temperatures of places si-tuated almost on the level of the sea, and under the same parallels.
| Lat. | Elevationin Feet. | Mean Temp. | |
| Buda, ‒ ‒ ‒ | 47°.29 | 512 | 51°.08 |
| Paris, ‒ ‒ ‒ | 48.50 | 116 | 51.08 |
| Vienna, ‒ ‒ ‒ | 48.12 | 551 | 50.54 |
| Manheim, ‒ ‒ | 49.20 | 384 | 50.18 |
| Elevationin Feet. | Mean Temp. | |
| Geneva, ‒ ‒ ‒ | 1177 | 49°.28 |
| Zurich, ‒ ‒ ‒ | 1437 | 47.84 |
| Munich, ‒ ‒ ‒ | 1711 | 50.74 |
| Berne, ‒ ‒ ‒ | 1755 | 49.28 |
| Marschling, ‒ ‒ | 1834 | 51.98 * |
| Coire, ‒ ‒ ‒ | 1991 | 48.92 † |
| Places situated between46°—47° of NorthLat. | Elevations. | Mean Temperatures. | |||
| Metres. | Feet. | Of theYear. | Of theColdestMonths. | Of theWarmestMonths. | |
| Level of the sea, ‒ | 0 | 53°.60 | 36°.32 | 69°.80 | |
| Geneva, ‒ ‒ | 359 | 1177 | 49.64 | 34.16 | 66.56 |
| Tegernsee, ‒ ‒ | 744 | 2440 | 42.44 | 22.10 | 59.36 |
| Peissenberg, ‒ | 995 | 3264 | 41.00 | 20.84 | 57.02 |
| Chamouni, ‒ ‒ | 1028 | 3372 | 39.20 | 55.40 | |
| Hospice de St Gothard, | 2076 | 6809 | 30.38 | 15.08 | 46.22 |
| Col de Géant, ‒ | 3436 | 11270 | 21.20 | 36.50 | |
| Metres. | Feet. | Mean Temp. of Limitof Perpetual Snows. | |
| At the Equator, | 4800 | 15,744 | 34°.70 |
| In Temperate Zone, | 2700 | 8,856 | 25.34 |
| In Frigid Zone, inLat. 68°—69°, | 1050 | 3,444 | 21.20 |
* Observations Astronomiques, tom. i. p. 136.|277| 47° to beds of the atmosphere equally elevated. This determi-nation is founded on stationary observations, and indicates themean state of the atmosphere. General physics has its numeri-cal elements, as well as the system of the world; and these ele-ments, so important in the theory of barometrical measurementsand in that of refractions, will be perfected in proportion as na-tural philosophers shall direct their attention to the study of ge-neral laws.
| Height, in | Equatorial Zone, from 0°——10°. | Temperate Zone, from 45°——47°. | |||
| Metres. | Feet. | MeanTemp. | Diff. | MeanTemp. | Diff. |
| 0 | 0 | 81°.50 | 10°.26 | 53°.60 | 12°.60 |
| 974 | 3195 | 71.24 | 6.12 | 41.00 | 9.36 |
| 1949 | 6393 | 65.12 | 7.38 | 31.64 | 8.28 |
| 2923 | 9587 | 57.74 | 13.14 | 23.36 | |
| 3900 | 12792 | 44.60 | 9.90 | ||
| 4872 | 15965 | 34.70 | |||
| Metres. | Cent. | Fahr. | Metres. | |||
| Equinoctial Zone, | 0—4900 | 1° | or | 1°.8 | for | 187 * |
| Temperate Zone, | 0—2900 | 1° | or | 1°.8 | for | 174 |
* This is the mean result or the measure of the distribution of heat in thewhole column of air. The partial results are from the back of the Andes.
| Heights inMetres. | Cent. | Fahr. | Metres. | ||
| 0—1000 | 1° | or | 1°.8 | for | 170 |
| 1000—2000 | 1 | or | 1.8 | for | 294 |
| 2000—3000 | 1 | or | 1.8 | for | 232 |
| 3000—4000 | 1 | or | 1.8 | for | 131 |
| 4000—5000 | 1 | or | 1.8 | for | 180 |
| Cent. | Fahr. | Metres. | ||
| Equinoctial zone, ‒ | 1° | or | 1°.8 | 190 |
| Parallels of 45°—47°, ‒ | 1° | or | 1°.8 | 160—172 * |
temperature of October is even a little below that of the whole year, it is probablethat the height of the plain of Great Thibet exceeds from 2900 to 3000 metres.—See my Memoir on the Mountains of India in the Ann. de Chim. et de Phys. 1817. Note by the Editor. As the cold meridian of the globe passes through the plains of Great Thibet,we conceive that the mean temperature of Lat. 29° in that plain, when reduced tothe level of the sea, will be about 65°, and therefore that the height of the plain ofGreat Thibet will not exceed 2800 metres or 9184 feet.—D. B.* Saussure gives for the summer 160 metres, (525 feet); for winter 230, (754feet); and for the whole year 195, (640 feet). M. Ramond gives 165, (538 feet).M. D’Aubuisson 173 metres, (567 feet).—See Journ. de Phys. tom. lxxi. p. 37.; De la Formul. Barometr. p. 189.; and my Recueil d’Obs. Astron. tom. i. p. 129.† As the temperature varies very little in the course of a whole year in theequinoctial zone, we may form a pretty correct idea of the climate of the Cordil-|280| leads us to an exact knowledge of the numerical ratios betweenthe elevations and the latitudes, ratios which we find indicatedwith little precision in works on physical geography. The following are the results which I have obtained from exactdata in the temperate zone, from the plains to 1000 metres of ele-vation. Every hundred metres of perpendicular height, dimi-nishes the mean temperature of the year, by the same quantitythat a change of 1° of latitude does in advancing towards thePole. If we compare only the mean temperature of summer,the first 1000 metres are equivalent to 0°.81 Fahr. From 40°to 50° of latitude, the mean heat of the plains in Europe de-creases in Europe 12°.6 of Fahr.; and this same decrease oftemperature takes place on the declivity of the Swiss Alps from0 to 1000 metres of elevation.
| Differences of Latitude, Compared with Differences ofElevation. | MeanHeat of theYear. | MeanHeat ofSummer. | MeanHeat ofAutumn. |
| I. At the Level of the Sea. | |||
| a. Latitude, 40°, ‒ | 63°.14 | 77°.00 | 62°.60 |
| b. Latitude, 50°, ‒ | 50.54 | 64.40 | |
| II. On the Declivity of Mountains. | |||
| a. At the foot in 46° of Lat. | 53.60 | 68.00 | 51.80 |
| b. At an elevation of 1000 metres, | 41.00 | 58.46 | 42.80 |
leras, by comparing them to the temperature of certain months in France or inItaly. We find in the plains of Orinoco the month of August of Rome; at Po-payan, (2988 feet), the month of August of Paris; at Quito (4894 feet), the monthof May; in the Paramos, (5904 feet), the month of March at Paris.|281| too cold for the cultivation of plants useful to man. M. DeCandolle, indeed, to whom the geography of vegetables owes somany valuable observations, has seen the vine cultivated in thesouth of France at 800 metres (2624 feet) of absolute height,when, under the same meridian, this same cultivation went onwith difficulty at 4º of latitude farther north; so that if we con-sider only the ratios in France, an elevation of 100 metres, (328feet), appears to correspond, not to 1°, but to half a degree of la-titude *. (To be concluded in next Number.)
* See my Prolegomena de Distributione Plantarum, p. 151.—163. The smalldifferences between the numbers given in the Prolegomena and in this Memoir,written subsequently, should be ascribed to the constant desire which I have hadto perfect the mean results.|28|
On Isothermal Lines, and the Distribution of Heatover the Globe. By Baron Alexander de Humboldt. (Concluded from Vol. IV. p. 281.)
* Baron von Buch, in the Bibl. Brit. tom. xix. p. 263.; Saussure, Voyages, sect. 1418.; Wahlenberg, De Veget. Helvet. Pl. 77.—84.; Gilbert, Annalen, 1812,p. 150. 160. 277.; Lambert, Pyrometrie, p. 296. Dr Roebuck appears to havebeen the first who entertained exact notions on the temperature of springs, andupon their relation to the mean temperature of the air; Phil. Trans. 1775, vol. lxv.p. 461.|29| mean temperature of the ambient air. The temperature of theinterior of the earth is, at
| Lat. | Temp.Fahr. | Lat. | Temp.Fahr. | ||
| Vadso, | 70°.0 | 35°.96 | Paris, | 48° 50′ | 53.°6 |
| Berlin, | 52.31 | 49.28 | Cairo, | 30 2 | 72.5 |
| Alt. inFeet. | Temp.Fahr. | |
| Spring of Utliberg, near Zurich, ‒ | 1532 | 48°.92 |
| Ditto of Rossbaden at St Gothard, ‒ | 7016 | 38.30 |
| Alt. inFeet. | Temp.Fahr. | |
| Springs of Cumanacoa, ‒ ‒ | 1,148 | 72°.5 |
| Ditto Montserrate, above Santa Fé de Bogota, | 10,680 | 59.9 |
| Ditto in the Mine of Hualgayoc in Peru, | 11,759 | 53.24 |
| Zone of 30°—55°. | Lat. | Mean Temp.of Air,Fahr. | Temp. of theInterior ofthe Earth. |
| Cairo, ‒ ‒ | 30° 2′ | 72°.68 | 72°.50 |
| Natchez, ‒ ‒ | 31 28 | 64.76 | 64.94 |
| Charlestown, ‒ ‒ | 33 0 | 63.14 | 63.50 |
| Philadelphia, ‒ ‒ | 39 56 | 53.42 | 52.16 |
| Geneva, ‒ ‒ ‒ | 46 12 | 49.28 | 50.74 |
| Dublin, ‒ ‒ ‒ | 53 21 | 49.10 | 49.28 |
| Berlin, ‒ ‒ ‒ | 52 31 | 47.30 | 49.28 |
| Kendal, ‒ ‒ | 54 17 | 46.22 | 47.84 |
| Keswick, ‒ ‒ | 54 33 | 48.02 | 48.56 |
| Zone of 55°—70°. | |||
| Carlscrona, ‒ ‒ | 56 6 | 46.04 | 47.30 |
| Upsal, ‒ ‒ | 59 51 | 41.90 | 43.70 |
| Umeo, ‒ ‒ | 63 50 | 33.26 | 37.22 |
| Vadso, ‒ ‒ | 70 0 | 29.66 | 35.96 |
| Alt. inFeet. | Temperature. | ||
| Springs. | Air. | ||
| Rigi Kaltebad, ‒ | 4717 | 43°.7 | 38°.12 |
| Pilate, ‒ ‒ | 4858 | 41.0 | 37.40 |
| Blancke Alp, ‒ | 5786 | 37.4 | 35.78 |
| Rossbaden, ‒ ‒ | 7016 | 38.3 | 31.38 |
* At Funchal in Madeira, the temperature of caverns appears to be 61°.16, andconsequently 7°.2 below that of the air.—Phil. Trans. 1778, p. 372.|31| coasts, and perhaps even in continents of small extent, the inte-rior heat of the earth is modified by the proximity of the strataof rocks on which the waters of the ocean rest. I have considered successively in this memoir, the distributionof heat,
- 1. At the surface of the globe.
- 2. On the declivity of mountains.
- 3. In the ocean.
- 4. In the interior of the earth.
In the following general Table of the distribution of heat,the temperatures are expressed in degrees of Fahrenheit; thelongitudes are reckoned from east to west of the meridianof the observatory of Greenwich. The mean temperatures ofthe seasons have been calculated, so that those of the months of December, January, and February, form the mean temperatureof Winter. An asterisk (*) is prefixed to those places whosemean temperatures have been most accurately determined, andin general by means of 8000 observations. The isothermallines have a convex summit in Europe, and two concave sum-mits in Asia and Eastern America |32|
| Isother-malBands. | Names of Places. | Position. | MeanTemp. ofthe Year. | Distribution of Heat in the different Seasons. | Maximum and Minimum. | ||||||
| Lat. | Long. | Heightin Feet. | Mean Temp.of Winter. | Mean Temp.of Spring. | Mean Temp.of Summer. | Mean Temp.of Autumn. | Mean Temp. ofWarmest Month. | Mean Temp. ofColdest Month. | |||
| Isothermal Bands from32° to 41°. | Nain, ‒ | 57° 8′ | 61°20′ W | 0 | 26°.42 | — 0°.60 | 23°.90 | 48°.38 | 33°.44 | 51°.80 | —11°.20 1 |
| * Enontekies, | 68 30 | 20 47 E | 1356 | 26.96 | + 0.68 | 24.98 | 54.86 | 27.32 | 59.54 | — 0.58 2 | |
| Hospice de StGothard, | 46 30 | 8 23 E | 6390 | 30.38 | 18.32 | 26.42 | 44.96 | 31.82 | 46.22 | 15.08 3 | |
| North Cape, | 71 0 | 25 50 E | 0 | 32.0 | 23.72 | 29.66 | 43.34 | 32.08 | 46.58 | 22.10 4 | |
| * Uleo, ‒ | 65 3 | 25 26 E | 0 | 35.08 | 11.84 | 27.14 | 57.74 | 35.96 | 61.52 | 7.70 5 | |
| * Umeo, ‒ | 63 50 | 20 16 E | 0 | 33.26 | 12.92 | 33.80 | 54.86 | 33.44 | 62.60 | 11.48 6 | |
| * St Petersburg, | 59 56 | 30 19 E | 0 | 38.84 | 17.06 | 38.12 | 62.06 | 38.66 | 65.66 | 8.60 7 | |
| Drontheim, | 63 24 | 10 22 E | 0 | 39.92 | 23.72 | 35.24 | 61.24 | 40.10 | 64.94 | 19.58 8 | |
| Moscow, ‒ | 55 45 | 37 32 E | 970 | 40.10 | 10.78 | 44.06 | 67.10 | 38.30 | 70.52 | 6.08 9 | |
| Abo, ‒ | 60 27 | 22 18 E | 0 | 40.28 | 20.84 | 38.30 | 61.88 | 40.64 | — | — 10 | |
| Isothermal Bands from 41° to 50°. | * Upsal, ‒ | 59 51 | 17 38 E | 0 | 42.08 | 24.98 | 39.38 | 60.26 | 42.80 | 62.42 | 22.46 11 |
| * Stockholm, ‒ | 59 20 | 18 3 E | 0 | 42.26 | 25.52 | 38.30 | 61.88 | 43.16 | 64.04 | 22.82 12 | |
| Quebec, ‒ | 46 47 | 71 10 W | 0 | 41.74 | 14.18 | 38.84 | 68.00 | 46.04 | 73.40 | 13.81 13 | |
| Christiania, ‒ | 59 55 | 10 48 E | 0 | 42.8 | 28.78 | 39.02 | 62.60 | 41.18 | 66.74 | 28.41 14 | |
| * Convent ofPeyssenburg, | 47 47 | 10 34 E | 3066 | 42.98 | 28.58 | 42.08 | 58.46 | 42.98 | 59.36 | 30.20 15 | |
| * Copenhagen, | 55 41 | 12 35 E | 0 | 45.68 | 30.74 | 41.18 | 62.60 | 48.38 | 65.66 | 27.14 16 | |
| * Kendal, ‒ | 54 17 | 2 46 W | 0 | 46.22 | 30.86 | 45.14 | 56.84 | 46.22 | 58.10 | 34.88 17 | |
| Malouin Islands, | 51 25 | 59 59 W | 0 | 46.94 | 39.56 | 46.58 | 53.06 | 48.46 | 55.76 | 37.40 18 | |
| * Prague, ‒ | 50 5 | 14 24 E | 0 | 49.46 | 31.46 | 47.66 | 68.90 | 50.18 | — | — 19 | |
| Gottingen, ‒ | 51 32 | 9 53 E | 456 | 46.94 | 30.38 | 44.24 | 64.76 | 48.74 | 66.38 | 29.66 20 | |
| * Zurich, ‒ | 47 22 | 8 32 E | 1350 | 47.84 | 29.66 | 48.20 | 64.04 | 48.92 | 65.66 | 26.78 21 | |
| * Edinburgh, ‒ | 55 57 | 3 10 W | 0 | 47.84 | 38.66 | 46.40 | 58.28 | 48.56 | 59.36 | 38.30 22 | |
| Warsaw, ‒ | 52 14 | 21 2 E | 0 | 48.56 | 28.76 | 47.48 | 69.08 | 49.46 | 70.34 | 27.14 23 | |
| * Coire, ‒ | 46 50 | 9 30 E | 1876 | 48.92 | 32.36 | 50.00 | 63.32 | 50.36 | 64.58 | 29.48 24 | |
| Dublin, ‒ | 53 21 | 6 19 W | 0 * | 49.10 | 39.20 | 47.30 | 59.54 | 50.00 | 61.16 | 35.42 25 | |
| Berne, ‒ | 46 5 | 7 26 E | 1650 | 49.28 | 32.00 | 48.92 | 66.56 | 49.82 | 67.28 | 30.56 26 | |
| * Geneva, ‒ | 46 12 | 6 8 E | 1080 | 49.28 | 34.70 | 47.66 | 64.94 | 50.00 | 66.56 | 34.16 27 | |
| * Manheim, ‒ | 49.29 | 8 28 E | 432 | 50.18 | 38.80 | 49.64 | 67.10 | 49.82 | 68.72 | 33.44 28 | |
| Vienna, ‒ | 48 12 | 16 22 E | 420 | 50.54 | 32.72 | 51.26 | 69.26 | 50.54 | 70.52 | 26.60 29 | |
| Isothermal Bands from 50° to 59°. | * Clermont, ‒ | 45 46 | 3 5 E | 1260 | 50.00 | 34.52 | 50.54 | 64.40 | 51.26 | 66.20 | 28.04 30 |
| * Buda, ‒ | 47 29 | 19 1 E | 494 | 51.08 | 33.98 | 51.08 | 70.52 | 52.34 | 71.60 | 27.78 31 | |
| Cambridge, (U.S.) | 42 25 | 71 3 W | 0 | 50.36 | 33.98 | 47.66 | 70.70 | 49.82 | 72.86 | 29.84 32 | |
| * Paris, ‒ | 48 50 | 2 20 E | 222 | 51.08 | 38.66 | 49.28 | 64.58 | 51.44 | 65.30 | 36.14 33 | |
| * London, ‒ | 51 30 | 0 5 W | 0 | 50.36 | 39.56 | 48.56 | 63.14 | 50.18 | 64.40 | 37.76 34 | |
| Dunkirk, ‒ | 51 2 | 2 22 E | 0 | 50.54 | 38.48 | 48.56 | 64.04 | 50.90 | 64.76 | 37.75 35 | |
| Amsterdam, | 52 22 | 4 50 E | 0 | 51.62 | 36.86 | 51.62 | 65.84 | 51.62 | 66.92 | 35.42 36 | |
| Brussels, ‒ | 50 50 | 4 22 E | 0 | 51.80 | 36.68 | 53.24 | 66.20 | 51.08 | 67.28 | 35.60 37 | |
| * Franeker, ‒ | 52 36 | 6 22 E | 0 | 51.80 | 36.68 | 51.08 | 67.28 | 54.32 | 69.08 | 32.90 38 | |
| Philadelphia, | 39 56 | 75 16 W | 0 | 53.42 | 32.18 | 51.44 | 73.94 | 56.48 | 77.00 | 32.72 39 | |
| New York, | 40 40 | 73 58 W | 0 | 53.78 | 29.84 | 51.26 | 79.16 | 54.50 | 80.78 | 25.34 40 | |
| * Cincinnati, ‒ | 39 6 | 82 40 W | 510 | 53.78 | 32.90 | 54.14 | 72.86 | 54.86 | 74.30 | 30.20 41 | |
| St Malo, ‒ | 48 39 | 2 1 W | 0 | 54.14 | 42.26 | 52.16 | 66.02 | 55.76 | 66.92 | 41.74 42 | |
| Nantes, ‒ | 47 13 | 1 32 W | 0 | 54.68 | 40.46 | 54.50 | 68.54 | 55.58 | 70.52 | 39.02 43 | |
| Pekin, ‒ | 39 54 | 116 27 E | 0 | 54.86 | 26.42 | 56.30 | 82.58 | 54.32 | 84.38 | 24.62 44 | |
| * Milan, ‒ | 45 28 | 9 11 E | 390 | 55.76 | 36.32 | 56.12 | 73.04 | 56.84 | 74.66 | 36.14 45 | |
| Bourdeaux, ‒ | 44 50 | 0 34 W | 0 | 56.48 | 42.08 | 56.48 | 70.88 | 56.30 | 73.04 | 41.00 46 | |
| IsothermalBand from59° to 63°. | Marseilles, ‒ | 43 17 | 5 22 E | 0 | 59.00 | 45.50 | 57.56 | 72.50 | 60.08 | 74.66 | 44.42 47 |
| Montpellier, | 43 36 | 3 52 E | 0 | 59.36 | 44.06 | 56.66 | 75.74 | 60.98 | 78.08 | 42.08 48 | |
| * Rome, ‒ | 41 53 | 12 27 E | 0 | 60.44 | 45.86 | 57.74 | 75.20 | 62.78 | 77.00 | 42.26 49 | |
| Toulon, ‒ | 43 7 | 5 50 E | 0 | 62.06 | 48.38 | 60.80 | 75.02 | 64.40 | 77.00 | 46.40 50 | |
| Nangasacki, | 32 45 | 129 55 E | 0 | 60.80 | 39.38 | 57.56 | 82.94 | 64.22 | 86.90 | 37.40 51 | |
| * Natchez, ‒ | 31 28 | 90 30 W | 180 | 64.76 | 48.56 | 65.48 | 79.16 | 66.02 | 79.70 | 46.94 52 | |
| Isotherm-al Bandfrom 68°to 77°. | * Funchal, ‒ | 32 37 | 16 56 W | 0 | 68.54 | 64.40 | 65.84 | 72.50 | 72.32 | 75.56 | 64.04 53 |
| Algiers, ‒ | 36 48 | 3 1 E | 0 | 69.98 | 61.52 | 65.66 | 80.24 | 72.50 | 82.76 | 60.08 54 | |
| Isotherm-al Bandsabove77°. | * Cairo, ‒ | 30 2 | 31 18 E | 0 | 72.32 | 58.46 | 73.58 | 85.10 | 71.42 | 85.82 | 56.12 55 |
| * Veracruz, ‒ | 19 11 | 96 1 W | 0 | 77.72 | 71.96 | 77.90 | 81.50 | 78.62 | 81.86 | 71.06 56 | |
| * Havannah, ‒ | 23 10 | 82 13 W | 0 | 78.08 | 71.24 | 78.98 | 83.30 | 78.98 | 83.84 | 69.98 57 | |
| * Cumana, ‒ | 10 27 | 65 15 W | 0 | 81.86 | 80.24 | 83.66 | 82.04 | 80.24 | 84.38 | 79.16 58 | |
* See Edinburgh Transactions, vol. ix. p. 209.—Ed. |36| 23 Guittard. Only three years. Mean temp. a little toohigh. Eastern part of Europe. A continental climate. 24 Four years of observations, by M. de Salis Sewis, calcu-lated by M. Wahlenberg. Mountains of the Grisons. 25 Kirwan. Irish Trans. viii. 203. and 269. Specimen ofthe climate of the islands. Coldest days, 23°; interior of theground, 49°.28. Hamilton. 26 The climate of Berne is a continental climate, in compari-son with that of Geneva; there is no lake near it. 27 Seven years of observations. Saussure. Mean temp. 50°74. Voy. § 1418. I find the mean temp. from 1796—1815, 49°.7.Interior of the earth, 51°.98. Pictet, Bibliotheque Brit. 1817,iv. 109. 28 Six years. 29 Austria. Berlin, Lat. 52° 31′; mean temp. probably 46°.4to 47°.3; according to Beguelin, 48°.74; springs, 49°.28. Ra-tisbon, Lat. 49°; height, 1,104 feet; mean temp. 47°.66. Mu-nich, Lat. 48° 8′; height, 1,608 feet; mean temp. 50°.74. 30 Ramond. Seven years of excellent observations. Themean of the months, at noon, well ascertained; winter, 39°.92;spring, 57°.02; summer, 70°.88; autumn, 57°.92. Mem. Inst. 1812, p. 49. Cotte, mean temp. 51°.26. 31 Wahlenberg, Flor. Carp. p. 90. Continental climate.Height of the observatory, 474 feet. 32 Two years, near Boston, in New England. Transatlanticclimate. The thermometer sometimes descends to 0°. 33 Eleven years (1803—1813) of observations made at theobservatory. A greater number of years will, perhaps, give themean temp. a little higher. Vaults, 53°.06. Kirwan finds forParis, from seven years of observations of unequal value, 51°.62;he fixes upon 52°.7. Cotte, from 29 years of observations, (Journ. de Phys. 1782, July), 53°.24. Cotte, for 33 years,(1763—1781, Mem. Instit. iv. 266.), 52°.34. The extraordinaryyear of 1816 offers the mean temp. of 48°.74; winter, 37°.04;spring, 48°.92; summer, 59°.54; autumn, 50°: the precedingyear, 1815, offers a mean temp. of 50°.74; winter, 37°.04; spring,52°.7; summer, 62°.78; autumn, 50°.74. Arago. Mean temp.of Montmorency, for 33 years, 50°.74; height, 498 feet. Cotte, |37| Strasburg, Lat. 48° 34′; height, 480 feet; mean temp. 49°.28.Herrenschneider. 34 Dr Young. Mean temp. varies from 47°.84 to 51°.62, (Lectures, ii. 453.) Cavendish, (Trans. 1788, p. 61.), 48°.74,Roebuck, Hunter, and Kirwan, 51°.62. Horsley, 51°.26. Ac-cording to Kirwan, the four seasons in London are, 39°.56, 50°.9,64°.76, 51°.98; at Paris, 36°.68, 51°.08, 65°.84, 52°.52; fromwhıch results, London, 51°.62; Paris, 51°.44. Cotte (Journ. dePhys. xxxix. 36.) thinks London is 51°.26, and Paris, 52°.34.The difference which we observe in cultivated plants dependsless upon mean temp. than upon direct light, and the serenityof the atmosphere. 35 Seven years. Cotte. Lisle, 48°.38; Rouen, 51°.44;Cambray, 51°.98; Soissons, 53°.42; Rethel, 53°.24; Metz, 52°.88;Nancy, 51°.98; Etampes, 51°.08; L’Aigle, 50°.9; Brest, 54°.14;Mayenne, 51°.98. 36 Mohr, and Van Swinden. Five years. 37 Thirteen years. Temperature rather too high? 38 Eleven years. Van Swinden. From 1771—1783. Meantemp. 51°.26. 39 Concave transatlantic summit. Seven years of observa-tions give 54°.86; for the four seasons, 33°.98, 53°.06, 75°.2,56°.12. Rush, 52°.52, (Drake’s View of Cincin. p. 116.) Coxe,54°.14. M. Legaux finds for 17 years, for Springmill on theSchuylkill, Lat. 40° 50′; mean temp. 53°.42. Springs, nearPhiladelphia, 54°.86, Warden. 40 Two years only. Retif de la Serve. The thermometersometimes descends to — 4° in the parallel of Naples! Springs,54°.86. Ipswich, Lat. 42° 38′; mean temp. 50°. Williamsburg,in Virginia, 58°.1. Cotte and Kirwan. Transatlantic climates. 41 Transatlantic climates west of the Alleghanys. Good ob-servations, from 1806—1813. Col. Mansfield, (Drake, p. 93.) Minimum of the winter, from 5° to — 9°.4; Jan. 1797, as lowas — 16°.6, for 39° latitude. Maximum 89°.6 to 107°.6 in theshade, without reflection; \( \frac{1}{3} \) of all the winds SW.; springs nearCincinnati, 54°.32. Little snow falls; but it is abundant betweenLat. 40° and 42°. 42 Three years only. Bougourd. Dijon, height, 810 feet; |38| Lat. 47° 19′; mean temp. 50°.9. Besançon, height, 804 feet;Lat. 47° 14′; mean temp. 51°.26. 43 Six years. Duplessis, and Boudan. Temperature of thesummer too high? Rochelle, 53°.06; Poitiers, 52°.7. 44 Amyot. Six years. Concave. Asiatic summit. Threemonths below 32°, as at Copenhagen; the summer like that atNaples. 45 One of the best determined points. The years 1789—1812are calculated in decads of days. Observations of the Astrono-mer Reggio, April, 55°.76; Oct. 58°.1. The two decads whichapproach the nearest to the mean temp. of the year, are, the firstof April, 53°.24; and the last of Oct. 54°.68. The mean temps.for January have varied in 10 years from 24°.98 to 38°.48;those of July, from 71°.42 to 78°.44; the mean of the years,from 54°.5 to 57°.2. (Reggio, taking only 24 maxima and mi-nima in a year for 1763—1798; mean temp. 55.4, Ephem. Mil. 1779, p. 82.) 46 Ten years. Guyot. Lyons, 528 feet, 55°.76. Mafra,near Lisbon, Lat. 38° 52′; height, 600 feet; mean temp. 56°.3,too small. Mem. de Lisbonne, ii. 105—158. 47 Seven years, (1777—1782). St Jacques de Sylvabelle.The thermometer sometimes descends to 23°. Cotte, Traité deMet. ii. 420.) 34 years (Raymond, in Mem. de la Soc. de Med. 1777, p. 86.) give 62°.06. Cotte (Journ. de Phys. xxxix. 21.)fixes it at 58°.64. Kirwan, at 61°.24. The observations madeat the Royal Observatory of Marseilles can alone decide. 48 Ten years. Nismes, 60°.26; Perpignan, 59°.54; Taras-con, 59°.9; Arles, 59°; Rieux, 57°.2: Montauban, 55°.58; To-nains, 54°.86; Dax, 54°.14; Rodez, 57°.02; Aix, 56°.66. Un-der the equator, 57°.74, at 9,000 feet of elevation. 49 William Humboldt. Calandrelli, 60°.08. The thermo-meter sometimes descends to 24°.5, and rises to 99°.5. Naples,67°.1; Toaldo, probably 63°.5; Florence, 61°.52; Tartini, toohigh; Lucca, 60°.44; Genoa, 60°.26; Bologna, 56°.3; Verona,55°.76; Venice, 56°.48; Padua, 56°.3. Kirwan regards it as anestablished fact, that in Europe the mean temp. in Lat. 40°, is61°.88; in Lat. 50°, 52°.52. 50 Only two years. Barberet, and d’Angos. Sheltered bymountains. Estimate a little too high. |39| 51 Japan. A single year. Voy. de Thunberg, p. 121. Cli-mate of islands. Under the Equator, 64°.4, at a height of 6000feet. 52 West of the Alleghanys, in Louisiana. Four years. Dun-bar. Transatlantic climate. 53 Madeira. Heberden. Climate of islands. St Croix, ofTeneriffe, 71°.42. The remainder of the island of Teneriffe, inthe plains, 69°.26. Buch. 54 Old observations of Tartebout. They appear good. Bag-dad, Lat. 33° 19′; according to Beauchamps, 73°.76. The fourseasons, 50°.74; 74°.64; 92°.66; 77°; but there was reflectionfrom a house. The thermometer falls to 29°.44. Under theEquator, at 3,000 feet high; mean temp. 71°.24. 55 The calculations are made from the observations of Nouet, (Decade, ii. 213.) The following are the mean temps. of the12 months: 58°.1; 56°.12; 64°.58; 77°.9; 78°.26; 83°.66;85°.02; 85°.82; 79°.16; 72°.32; 62°.96; 61°.24. (Niebuhr,72°.2.) Temp. of Joseph’s Well, 72°.5. Catacombs of Thebes,81°.5. Well of the great pyramid, surrounded by sand, 88°.16.Jomard. Bassora, on the Persian Gulf; mean temp. 77°.9;winter, 64°.04; summer, 90°.86; July, 93°.2. 56 Orta. Humboldt, Nouv. Esp. iv. 516. Jamaica, coast,80°.6. Blagden. 57 Ferrer, 1810—1812. Con. des Tems, 1817, p. 338.Wells of 10 feet deep; air, 75°.92; water, 74°.48; in 1812, maximum, Aug. 14. 86°; minimum, Feb. 20. 61°.52. Grot-tos, 81°.5. Humboldt, Observ. Astron. i. 134. 58 Humboldt. Pondicherry, 85°.1; Madras, 80°.42; Ma-nilla, 78°.08; Isle de France, coast, 80°.42.