Digitale Ausgabe

THE distribution of heat over the globe belongs to that kind ofphenomena, of which the general circumstances have been longknown, but which were incapable of being rigorously determined orsubmitted to exact calculation, till experience and observation fur-nished data from which the theory might obtain the corrections andthe different elements which it requires. The object of this memoir isto facilitate the collection of these data, to present results drawn froma great number of unpublished observations, and to group them ac-

---

* This highly valuable and extremely interesting Dissertation has imperativeclaims on the space of this Journal; but it occupies too much room to permit usto give it in detail: only those points relating especially to medical science will,therefore, be selected; but the extent of these even will render it necessary todivide our abstract into portions which may be inserted in the present and two orthree subsequent Numbers.—Edit. |288|cording to a method which has not yet been tried, though its utilityhas been recognized for more than a century in the exposition of thephenomena of the variation and dip of the magnetic needle. As thediscussion of individual observations will be published in a separatework, I shall at present limit myself to a simple sketch of the distri-bution of heat over the globe, according to the most recent and accu-rate data. Although we may not be able to refer the complexphenomena to a general theory, it will be of considerable importanceto fix the numerical relation by which a great number of scatteredobservations are connected, and to reduce to empirical laws the effectsof local and disturbing causes. The study of these laws will point outto travellers the problems to which they should direct their principalattention; and we may entertain the hope that the theory of the dis-tribution of heat will gain in extent and precision, in proportion asobservations shall be more multiplied, and directed to those pointswhich it is of most importance to illustrate. As the phenomena of geography and of vegetables, and in generalthe distribution of organized beings, depend on the knowledge of thethree co-ordinates of latitude, longitude, and altitude, I have been oc-cupied for many years in the exact valuation of atmospherical tempe-ratures; but I could not reduce my own observations without aconstant reference to the works of Cotte and Kirwan, the only oneswhich contain a great mass of meteorological observations obtained byinstruments and methods of very unequal precision. Having inhabitedfor a long time the most elevated plains of the New Continent, Iavailed myself of the advantages which they present for examining thetemperature of the superincumbent strata of air, not from insulateddata, the results of a few excursions to the crater of a volcano, butfrom the collections of a great number of observations made day afterday and month after month in inhabited districts. In Europe, and inall the Old World, the highest points of which the mean temperatureshave been determined are the convent of Peissenberg, in Bavaria, andthe hospice of St. Gothard.* The first of these is placed at 3264, andthe second at 6808, feet above the level of the sea. In America, agreat number of good observations have been made at Santa Fe deBegota and at Quito, at altitudes of 8,727 and 9,544 feet. The townof Huancavelica, containing 10,000 inhabitants, and possessing all theresources of modern civilization, is situated in the Cordilleras of thesouthern hemisphere, at 12,310 feet of absolute elevation; and themine of Santa Barbara, encircled with fine edifices, and placed a leagueto the south of Huancavelica, is a place fit for making regular obser-vations, at the height of 14,509 feet, which is double that of the hos-pice of St. Gothard. These examples are sufficient to prove how much our knowledge ofthe higher regions of the atmosphere, and of the physical condition ofthe world in general, will increase, when the cultivation of the sciences,

---

* 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.|289|so long confined to the temperate zone, shall extend beyond the tropicsinto those vast regions where the Spanish Americans have already de-voted themselves with such zeal to the study of physics and astronomy.In order to compare, with the mean heat of temperate climates, theresults which Mr. Bonpland and I obtained in the equinoctial regionsfrom the plains to the height of 19,292 feet, it was necessary to collecta great number of good observations made beyond the parallels of30° and 35°. I soon perceived how vague such a comparison was, if Iselected places under the meridian of the Cordilleras, or with a moreeastern longitude; and I therefore undertook to examine the resultscontained in the most recent works. I endeavoured to find, at everyten degrees of latitude, but under different meridians, a small numberof places whose mean temperature had been precisely ascertained, andthrough these, as so many fixed points, passed my isothermal lines, or lines of equal heat. I had recourse, in so far as the materials havebeen made public, to those observations the results of which have beenpublished; and I found, in the course of this easy, but long and mo-notonous, labour, that there are many mean temperatures pointed outin meteorological tables, which, like astronomical positions, have beenadopted without examination. Sometimes the results were in directcontradiction to the most recent observations, and sometimes it wasimpossible to discover from whence they were taken. Many good observations were rejected, solely because the absoluteheight of the place where they were made was unknown. This is thecase with Asia Minor, Armenia, and Persia, and of almost all Asia;and, while the equinoctial part alone of the New World presents al-ready more than five hundred points, the greater number of which aresimple villages and hamlets, determined by barometrical levelling, weare still ignorant of the height of Erzeroum, Bagdad, Aleppo, Teheran,Ispahan, Delhi, and Lassa, above the level of the neighbouring seas.Notwithstanding the intimate relation in which we have lately stoodwith Persia and Candahar, this branch of knowledge has not made anyprogress in the last fifty years. We are not authorized, however, on account of the decrease of tem-perature in the upper regions of the atmosphere, to confound themean temperatures of places which are not placed on the same level.In the Old World, good observations, which can alone be used forestablishing empirical laws, are confined to an extent between the pa-rallels of 30 and 70 degrees of latitude, and the meridians of 30° eastlongitude and 20° of west longitude. The extreme points of this re-gion are the island of Madeira, Cairo, and the North Cape. It is azone which is only a thousand nautical leagues, (one-seventh of thecircumference of the globe,) from east to west, and which, containingthe basin of the Mediterranean, is the centre of the primitive civiliza-tion of Europe. The extraordinary shape of this part of the world,the interior seas and other circumstances, so necessary for developingthe germ of cultivation among nations, have given to Europe a parti-cular climate, very different from that of other regions placed underthe same latitude. The temperature of the atmosphere and the magnetism of the globe, |290|cannot, like those phenomena which depend on one cause or on asingle centre of action, be disengaged from the influence of disturbingcircumstances, by taking the averages of many observations in whichthese extraneous effects are mutually destroyed. We must, however,guard against confounding, under the name of extraneous and disturb-ing causes, those on which the most important phenomena, such asthe distribution and the more or less rapid development of organiclife, essentially depend. Our object is to ascertain the quantity ofheat which every point of the globe annually receives, and, what is ofmost importance to agriculture and the good of its inhabitants, thedistribution of this quantity of heat over the different parts of theyear, and not that which is due to the solar action alone, to its alti-tude above the horizon, or to the duration of its influence, as measuredby the semidiurnal arcs. Moreover, we shall prove that the method of means is unfit for as-certaining what belongs exclusively to the sun, (inasmuch as its raysilluminate only one point of the globe,) and what is due both to thesun and to the influence of foreign causes. In distinguishing, as has long been done, between the solar and thereal climate, we must not forget that the local and multiplied causeswhich modify the action of the sun upon a single point of the globe,are themselves but secondary causes, the effects of the motion whichthe sun produces in the atmosphere, and which are propagated to greatdistances. If we consider separately (and it will be useful to do thisin a discussion purely theoretical,) the heat produced by the sun, theearth being supposed at rest and without an atmosphere, and the heatdue to other causes regarded as disturbing ones, we shall find that thislatter part of the total effect is not entirely foreign to the sun. Theinfluence of small causes will scarcely disappear by taking the meanresult of a great number of observations; for this influence is not li-mited to a single region. By the mobility of the aerial ocean, it is propagated from one continent to another. Every where in the re-gions near the polar circles, the rigors of the winters are diminishedby the admixture of the columns of warm air, which, rising above thetorrid zone, are carried towards the poles: every where in the tempe-rate zone, the frequent west winds modify the climate, by transportingthe temperature of one latitude to another.* When we reflect, be-sides, on the extent of seas, on the form and prolongation of continents,either in the two hemispheres, or to the east and west of the meridiansof Canton and of California, we shall perceive that, even if the numberof observations on the mean temperature were infinite, the compensa-tion would not take place. It is, then, from the theory alone that we must expect to determinethe distribution of heat over the globe, in so far as it depends on theimmediate and instantaneous action of the sun. It does not indicatethe degrees of temperature expressed by the dilatation of the mercuryin a thermometer, but the ratios between the mean annual heat at theequator, at the parallel of 45°, and under the polar circle; and it

---

* Raymond, Memoire sur la Formule Baromet. p. 108 and 113.|291|determines the ratios between the solstitial and equinoctial heats indifferent zones. By comparing the results of calculation, not with themean temperature drawn from observations made under different lon-gitudes, but with that of a single point of the earth’s surface, we shallset out with that which is due to the immediate action of the sun andto the whole of the other influences, whether they are solar or local,or propagated to great distances. This comparison of theory with ex-perience will present a great number of interesting relations. In the year 1693, previous to the use of comparable thermometers,and to precise ideas of the mean temperature of a place, Halleylaid the first foundations of a theory of the heating action of the sununder different latitudes.* He proved that these actions might com-pensate for the effect of the obliquity of the rays. The ratios whichhe points out do not express the mean heat of the seasons, but the heatof a summer-day at the equator and under the polar circle, which hefinds to be as 1·834 to 2·310. In detailing the actual state of our knowledge on the distribution ofheat, I have shown how dangerous it is to confound the results ofobservation with theoretical deductions. The heat of any point of theglobe depends on the obliquity of the sun’s rays and the continuanceof their action, on the height of the place, on the internal heat andradiation of the earth in the middle of a medium of variable tempera-ture; and, in short, upon all those causes which are themselves theeffects of the rotation of the earth and the inequal arrangement ofcontinents and seas. Before laying the foundation of a system, wemust group the facts, fix the numerical ratios, and, as I have alreadypointed out, submit the phenomena of heat, as Halley did those ofterrestrial magnetism, to empirical laws. In following this method, Ihave first considered whether the method employed by meteorologistsfor deducing the mean temperature of the year, the month, and theday, is subject to sensible errors. Assured of the accuracy of the nu-merical averages, I have traced upon a map the isothermal lines,analogous to the magnetic lines of dip and variation. I have consi-dered them at the surface of the earth in a horizontal plane, and onthe declivity of mountains in a vertical plane. I have examined theincrease of temperature from the pole to the equator, which is inequalunder different meridians; the distribution of the same quantity ofheat over the different seasons, in the same isothermal parallel, andunder different latitudes; the curve of perpetual snows, which is nota line of equal heat; the temperature of the interior of the earth,which is a little greater towards the north, and in high mountains, thanthe mean temperature of the atmosphere under the same parallel; and,lastly, the distribution of heat in the ocean, and the position of thosebands, which may be called bands of the warmest waters. As thelimits of this extract will not permit me to enter, in a detailed manner,upon these different discussions, I shall confine myself solely to theprincipal results. It was formerly the custom to take the maximum and minimum of

---

* Phil. Trans. 1693, p. 878.|292|temperature observed in the course of a year, and to consider half thesum as the mean temperature of the whole year. In order to diminish the errors of the method of annual extremes, itwas perceived, though very late, that it was necessary to subdivide thecurve which expresses the variation of temperature. Twenty-fourextremes divided among twelve months of the year, give an annualmean more exact than the two extremes of all the observations. Theordinates do not increase uniformly and uninterruptedly up to themaximum of the year, and there are partial inflexions sufficiently re-gular. The more we subdivide, and the more we know the terms inthe series, the more will these terms approximate, and the less errorwill there be in the supposition of an arithmetrical progression, and inthat of the equidistance of the different maxima and minima of tempe-rature. These considerations enable us to appreciate the three methodsaccording to which observations are at present made. 1. Observationsare made three times a-day, at sunrise and sunset, and at two o’clockin the afternoon. This was done at Geneva, during the three years1796, 1797, and 1798. In the observations, the hour of mid-day waspreferred to that of sunset. 2. Observations are made twice everyday, at the two periods which are supposed to give the maximum andthe minimum,—namely, at sunrise and at two o’clock in the afternoon.3. Observations are made once a-day, at an hour which, in differentseasons, has been found to represent the mean temperature of the day.It is thus that Mr. Raymond, by a judicious induction, has provedthat the height of the barometer at mid-day gives, in our climates, themean atmospherical pressure, corrected for the diurnal variation. In calculating* a great number of observations made between theparallels of 46° and 48°, I have found that a single observation atsunset gives a mean temperature, which differs only some tenths of adegree from that which is deduced from observations made at sunriseand at two o’clock. The deviations of different months do not exceed1·8, and they are very regularly positive or negative, according tothe order of the seasons. Mr. Arago† has examined for seven yearsthe observations of noon. They give for Paris 5·4 more than themean temperature of the whole year. Upon high mountains in thetemperate zone, the difference is scarcely 1·8.‡ By the applicationof coefficients, variable according to the latitude and the elevation, wemay deduce the true mean temperatures from observations made atany particular period of the day, nearly in the same manner as we canascertain the latitude of a place from altitudes of the sun, taken out ofthe meridian. If we do not stop at two observations of the maximum and mini-mum, but add a third observation, we commit an error more or lessserious, if we divide simply by three the sum of the observations,without attending to the duration of the partial temperatures and to

---

* De la Formule Barom. p. 213.† The mean of the observations at noon at Paris, was 56·84; at Clermont inAuvergne, (elevation, 1348 feet,) 56·30; at Strasburg, (elevation, 453 feet,)55·22.—Bulletin de la Soc. Philom. 1814, Oct. p. 95.‡ At the hospice of St. Gothard.—Ephem. Soc. Pal. 1785, p. 47.|293|the place which the third observation occupies between the last termsof the series.* Experience proves that the mean temperatures of theyear, obtained by two or three observations, do not differ sensibly, ifthe intermediate observation is sufficiently distant (four or five hours)from the observation of the maximum and minimum. Whenever,therefore, we do not take into account the duration of the intermedi-ate temperatures, we should prefer the two observations of the extremetemperature, which is the method most generally adopted. We shallcontent ourselves with pointing out the errors to which it is liable. Inour climates, the two extreme terms do not divide the series of twenty-fours into two equal parts. The maximum is an epoch nearly fixed:the rising of the sun retards or hastens it three hours. As we oughtto take into account the duration of the partial temperature, in orderto find the quantity of heat divided between the night and the day, wemust couple the maximum of one day with the minimum of the dayfollowing, and not be content with taking half the sum of all themaxima and minima of a month. In the ordinary method, we deter-mine only the mean temperature of the part of the day comprehendedbetween the rising of the sun and two o’clock in the afternoon; andwe take it for granted that the mean temperature is the same† fromtwo o’clock to sunrise next day. This double error, of want of equi-distance and of the coupling of observations, does not in general pro-duce errors of more than some tenths of degrees, sometimes in excess,and sometimes in defect, since the warm and cold days are mixed.‡ All the calculated results will err in defect, if the 365 ordinatesthrough which the curve of the year passes do not express an arithme-tical progression, and if the partial irregularities do not sensibly com-pensate one another. It is only on this supposition that we can judgeby the extreme terms of the series, of the sum of the terms; that is, ofthe partial temperatures. It is very obvious, that near the maximumthe increase ought to be more slow than in other points of the curveand that this increase in the temperature of the air ought to depend onthe sine of the sun’s altitude, and on the emission of the radiant heatof the globe.

---

* Example.—On the 13th June, at 4h in the morning, 46·4; at 2h in the after-noon, 55·4; and at 11h in the evening, 50°, (erroneously, 46·4, or 8° centig. inthe 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

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.† 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, ½ (50·0 + 66·2) × 8 = 450·4 for 8h = 472·0
	16h, ½ (51·8 + 62·6) × 16 = 915·2 for 16h = 929·6.

The method commonly employed gives ½ (50° + 62·6) = 56·3, and ½ (66·2 + 51·8)= 58·1. The errors being — 0·6 and + 0·9, sometimes positive and sometimesnegative.‡ The error disappears when days of equal temperature succeed one another.It amounts to 1·8, if the mean temperatures of two successive days differ from 7°to 9°, which however very rarely happens.|294| It appeared to me very important to establish, by observations madeat every hour, at different periods of the year, and under different la-titudes, the degree of confidence that can be placed in those resultswhich are called mean temperatures. I have selected from the registersof the Royal Observatory at Paris clear and calm days, which offeredat least ten or twelve observations. Under the equator, I have spentwhole days in determining the horary increments and decrements oftemperature, in marking the thermometer both in the shade and in thesun, and also the progress of evaporation and humidity; and, in orderto avoid calculation, I measured with a quadrant the altitude of thesun at each observation. I chose days and nights completely calm,and when the heavens were entirely free from clouds, because themass of vesicular vapours interrupts the radiation from the earth.The result of these experiments has been very satisfactory, and proveswhat had already been deduced from the coincidence between the tem-perature of the earth and the mean of daily observations, and fromthe regular progress of the mean temperatures of months in differentyears, that the effects of small disturbing causes may be compensatedby a great number of observations.* I have obtained analogous resultsby taking, for several months, the mean of 9 o’clock in the morning,of sunrise and midnight. I have computed the temperatures by thedistance of the maximum expressed in time, and on the supposition ofan arithmetical progression. I have found that, under the TorridZone, the morning curve, from sunrise to the maximum, differs veryregularly from the evening curve. In the morning, the true meantemperature, such as we find by taking the duration into account, isa little greater than half the sum of the extremes.† In the evening,

---

* 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.

The three last days show an equality of temperature which is very surprising, andwhich does not appear but in the true means.† Example.—Latitude 10°25′.

	Calculation of atrue mean bythe duration.	Supposition ofan arithmeticalpregression.
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

|295|the error is in a contrary direction, and the series of temperatures ap-proaches more to a progression by quotients. The differences do notin general exceed half a degree, and calculation proves that the com-pensation is regular. It would be curious to examine the effect whichthe radiation of the earth has on these horary effects, as the changes oftemperature at the surface do not follow the geometrical progression,in so far as they take place in a medium of uniform temperature. In order to avoid the use of an arbitrary measure, astronomers ex-press the diameters of the planets by taking that of the earth for unity.In like manner, I express the mean temperatures, not in parts of theequatorial heat, but by the arithmetical ratios which subsist betweenthis heat and that of the other parallels. This method frees us fromthe want of uniformity, which arises from the use of different thermo-meters. Instead of saying, that in Europe, under the parallel of 45°,the mean temperature is 13·4 Centigrade, or 56·12 of Fahrenheit, wesay that it is = 1·0°,487, and in lat. 55° = 1·0°,29. These arithme-tical ratios inform us of what is most interesting in the theory of thedistribution of heat, that, in thermometers whose zero is the point ofmelting ice, the mean temperatures under the latitude of 45° and 55°are, in our regions, the half and the third nearly of the equatorialtemperature, which I suppose to be 81·5. Having discussed the method of taking averages, and of reducingtemperatures to general expressions, we shall now proceed to tracethe course of the isothermal lines on the surface of the globe, and atthe level of the sea. From a slight attention to the difference of cli-mates, it has been remarked, more than a century ago, that the tem-peratures are not the same under the same parallels; and that, inadvancing 70° to the east or the west, the heat of the atmosphere suf-fers a sensible diminution. In pursuance of our method, we shallreduce these phenomena to numerical results, and show that places si-tuated under the same latitudes do not differ, in America and Europe,by the same number of degrees of temperature, as has been vaguelystated. This assertion would make us suppose that the isothermallines are parallel in the temperate zone.

		Lat.	MeanTemp.
I. Parallels of Georgia, of the State ofMississippi, of Lower Egypt, andMadeira.	Natchez ..........	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
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

|296|

		Lat.	MeanTemp.
III. Parallels of Pennsylvania, Jersey,Connecticut, Latium, and Romelia.	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	63 1
	Rome ............	41 53	60 4
	Difference ....	6 30	11 0
IV. Parallels of Canada, Nova Scotia,France, and the South of Germany.	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 South ofSweden, 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

This table* indicates the difference of climates, expressed by that ofthe mean temperature, and by the number of degrees in latitudewhich it is necessary to go northward in Europe, in order to find thesame quantity of annual heat as in America. As a place could not befound in the Old World whose mean temperature was 48°, the sameas that of Williamsburg, I have supplied it with an interpolation be-tween the latitudes of two points whose mean temperatures are 56·5and 59·4. By an analogous method, and by employing only goodobservations, I have found that 1. The isothermal line of 32° (0° centig.) passes between Uleo andEnontekies in Lapland, (lat. 66° to 68°; East long. from London19° to 22°,) and Table Bay in Labrador, (lat. 54° 0′; W. 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 Newfound-land, (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.)

---

* See my Prolegomena de Distributione Geographica Plantarum, secundum Cœlitemperiem et altitudinem montium, p. 68.|297| 4. The isothermal line of 59° (15° centig.) passes between Romeand Florence, (lat. 43° 0′, East long. 11° 40′,) and near Raleigh inNorth Carolina, (lat. 36° 0′, and West long. 76° 30′.) The direction of these lines of equal heat gives, for the two systemsof temperature which we know by precise observations,—viz. part ofthe middle and west of Europe, and that of the coast of America, thefollowing 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

If we call the mean equatorial temperature 1, we shall have the halfof this temperature in the Old World at 45°, and in the east of theNew World at 39° of lat. The mean temperatures decrease

	Latitude.				Temp.				Temp.
From	0°—20°		In the OldWorld,		3·6		In the NewWorld,		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

In both continents, the zone in which the mean temperature decreasesmost rapidly is comprehended between the parallels of 40° and 45°.Observation here presents a result entirely conformable to theory, forthe variation of the square of the cosine, which expresses the law ofthe temperature, is a maximum towards 45° of latitude. We have traced the direction of the isothermal lines from Europeto the Atlantic provinces of the New World, We have seen them ap-proach one another from parallelism towards the south, and convergetowards the north, particularly between the thermometric curves of41° and 50°: we shall now endeavour to pursue them to the west.North America presents 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 opposite toEurope and Asia,—viz. the chain of the Alleghanys and the RockyMountains, which divide the waters of the Missouri and the Columbia.Between these chains stretch the vast basin of the Mississippi, theplains of Lousiana and of the Tenesse, and the states of Ohio, thecentre of a new civilization. It is generally believed in America thatthe climate is more mild to the west of the Alleghany mountains, thanunder the same parallels in the Atlantic states. Mr. Jefferson hasestimated the difference at 3° of latitude; and the gleditsia mono-sperma, the catalpa, and the aristolochia sypho, and other vegetableproductions, are found so many degrees farther to the north, in thebasin of the Ohio, than on the coast of the Atlantic.* Mr. Volney has

---

* See my Essai sur la Geographie des Plantes, p. 154.|298| endeavoured to explain these phenomena by the frequency of thesouth-west winds, which drive back the warm air of the Gulf ofMexico towards these regions. A series of good observations, made,for seven years, by Colonel Mansfield at Cincinnati, on the banks ofthe Ohio, and recently published by Mr. Drake, in an excellent trea-tise on American Meteorology,* has removed the doubts which ob-scured this point. The thermometrical means prove that the isothermallines do not rise again in the regions of the west. The quantity ofheat which each point of the globe receives under the same parallels isnearly equal on the east and west of the Alleghany range, the wintersbeing only a little milder to the west, and the summers a little warmer.† The migrations of vegetables towards the north are favoured, in thebasin of the Mississippi, by the form and the direction of the valleywhich opens from the north to the south. In the Atlantic provinces,on the contrary, the valleys are transverse, and oppose great obstaclesto the passage of plants from one valley to another. If the isothermal lines remain parallel, or nearly so, to the equator,from the Atlantic shores of the New World to the east of the Mississippiand the Missouri, it cannot be doubted that they rise again beyondthe Rocky Mountains, on the opposite coast of Asia, between 35° and55° of latitude. Through 122° 40′ of west long. the isothermal lineof 50° Fahr. appears to pass almost as in the Atlantic part of the OldWorld, at 50° of lat. The western coasts of the two worlds resembleone another to a certain point.‡ But these returns of the isothermallines do not extend beyond 60°. The curve of 32° Fahr. is alreadyfound to the south of the Slave Lake, and it comes still farther southin approaching Lakes Superior and Ontario. In advancing from Europe towards the east, the isothermal linesagain descend,§ the number of fixed points being few. We can only

---

* Natural and Statistical View or Picture of Cincinnati and the Miami Country. 1 vol. 8vo. Cincinnati.† 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

|Spaltenumbruch|

Philadelphia. Lat. 39° 56′, West long. 75° 16′.
Winter,	32·2 Fahr.
Spring,	51·4
Summer,	73·9
Autumn,	56·5
Mean,	53·5

I have taken for Philadelphia the means between the observations of Coxe andRush. I have also referred, for correction, to the observations made by Mr.Legaux at Spring-Mill, upon the Schuylkill, to the north of Philadelphia. AsCincinnati is 512 feet above the level of the sea, its mean temp. is 1·4 too low.‡ 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

|Spaltenumbruch|

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

|299|employ those which are made in places whose known elevation allowsus to reduce the mean temperatures to the level of the sea. The fewgood materials which we possess have enabled us to trace the curves of32° and 55·4. We know even the nodes of the latter curve round thewhole globe. It 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 havehere pointed out only the empirical laws, under which are ranged thegeneral phenomena and the variations of the temperature which em-brace at once a vast extent of the globe. There are partial inflexions of the isothermal lines, which form, so to speak, particular systemsmodified by small local causes; such as the strange inflexion of thethermometric curves on the shores of the Mediterranean, betweenMarseilles, Genoa, Lucca, and Rome,* and those which determine thedifference between the climate of the western coast and the interior ofFrance. These last depend much less on the quantity of heat receivedby a part of the globe during the whole year, than upon the unequaldistribution of heat between winter and summer. It will one day beuseful to have, upon particular charts, the partial inflexions of theisothermal lines, which are analogous to the lines of soundings or ofequal declivity. The employment of graphical representations will throwmuch light upon phenomena which are deeply interesting to agricultu-rists. If, in place of geographical charts, we possessed only tablescontaining the co-ordinates of latitude, longitude, and altitude, agreat number of curious facts relative to the configuration and thesuperficial inequalities of continents would have remained for ever un-known. We have already found that, towards the north, the isothermal linesare neither parallel to the equator nor to one another; and it is onaccount of the want of parallelism that we have, in order to simplifysuch complicated phenomena, traced round the whole globe the curvesof equal heat. The position of the line of 32° acts like the magneticequator, whose inflexions in the South Sea modify the inclinations atgreat distances. We may even believe that, in the distribution of cli-mates, the line of 32° determines the position of the curve of greatestheat, which is as it were the isothermal equator; and that, in Americaand Asia, through 78° of west and 102° of east longitude, the torridzone commences more to the south of the tropic of Cancer, or that itthere presents temperatures of less intensity. An attentive examina-tion of the phenomena proves that this is not the case. Whenever weapproach the torrid zone below the parallel of 30°, the isothermallines become more and more parallel to one another and to the earth’s

---

* The elevation of Pekin is inconsiderable; that of Moscow is 984 feet. The ab-solute temperature of Madrid, to the west of Naples, is 59°; but the city iselevated 1978 feet above the level of the sea. |Spaltenumbruch|

	Lat.	MeanTemp.
Bologna,	44·29	56·3
Genoa,	44·25	60·6

|Spaltenumbruch|

	Lat.	MeanTemp.
Marseilles,	43·17	58·8
Rome,	41·53	60·4

|300|equator. The great colds of Canada and Siberia do not extend theiraction to the equatorial plains. If we have long regarded the OldWorld as warmer between the tropics than the New World, it is, 1st,because, till 1760, travellers used thermometers of spirit of wine, co-loured, and affected by light; 2d, because they observed it eitherunder the reflection of a wall or too near the ground, and when theatmosphere was filled with sand; and 3d, because, in place of calcu-lating the true mean, they used only the thermometric maximum andminimum. Good observations give, |Spaltenumbruch|

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

|Spaltenumbruch|

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

The mean temperature of the equator cannot be fixed beyond 81½°.Kirwan values it at 84°; but only two places of the earth wereknown, viz. Chandernagor and Pondicherry, to which old travellersattributed annual temperatures above 81½°. At Chandernagor, inlatitude 21·6, the mean temperature, according to Cotte, is 91·9; butthe Jesuit Boudier marked only the days when the thermometer wasabove 98·6 and below 57·2: and at Pondicherry, in latitude 11·55,the mean temperature, according to Cotte, is 85·3, and according toKirwan, 88°; but M. de Cossigny observed with a spirit-of-winethermometer. The distribution of heat over different parts of the year differs, notonly according to the decrease of the mean annual temperatures, butalso in the same isothermal line. It is this unequal division of the heatwhich characterizes the two systems of climate of Europe and AtlanticAmerica. Under the torrid zone, a small number of months arewarmer in the Old World than in the New. At Madras, for example,according to Dr. Roxburgh, the mean temperature of June is 89·4;at Abusheer, 93·2; but at Cumana I have found it only 84·6. With respect to the temperate zone, it has long been known that,from the parallel of the Canary Isles to the Polar Circle, the severityof the winter augments in a progression much more rapid than thesummers diminish in heat. It is also known that the climate of theislands and the coasts differs from that of the interior of continents,the former being characterized by mild winters and less temperatesummers. But it is the heat of summer particularly which affects theformation of the amylaceous and saccharine matter in fruits, and thechoice of the plants that ought to be cultivated. As the principal ob-ject of this memoir is to fix, after good observations, the numericalrelations between the unequal quantities of heat distributed over theglobe, we shall now compare the mean temperatures of three monthsof winter and summer under different latitudes, and show how the in-flections of the isothermal lines modify these relations. In followingthe curves of equal heat from west to east, from the basin of the Mis-sissippi to the eastern coasts of Asia, through an extent of 4000leagues, we are struck with the great regularity which appears in thevariations of the winter temperature. |301|

AFTER what has already been stated respecting the limits betweenwhich the annual heat divides itself on the same isothermal curve,it will be seen how far we are authorized to say, that the coffee-tree, the olive, and the vine, in order to be productive, require mean tem-peratures of 64·4, 60·8, and 53·6, Fahr. These expressions are trueonly of the same system of climate,—for example, of the part of theOld World which stretches to the west of the meridian of Mont Blanc;because, in a zone of small extent in longitude, while we fix the annualtemperatures, we determine also the nature of the summers and thewinters. It is known, likewise, that the olive, the vine, the varietiesof grain, and the fruit-trees, require entirely different constitutionsof the atmosphere. Among our cultivated plants, some, slightly sen-sible of the rigors of winter, require very warm, but not long, sum-mers; others require summers rather long than warm; while others,again, indifferent to the temperature of summer, cannot resist thegreat colds of winter. Hence it follows, that, in reference to the cul-ture of useful vegetables, we must discuss three things for each cli-mate: the mean temperature of the entire summer,—that of thewarmest month,—and that of the coldest month. I have publishedthe numerical results of this discussion in my Prolegomena de Distri-butione Geographica Plantarum, secundum Cœli Temperiem; and Ishall confine myself at present to the limits of culture of the olive andthe vine. The olive is cultivated in our continent between the paral-lels of 36° and 40°, wherever the annual temperature is from 62·6to 58·1, where the mean temperature of the coldest month is not be-low from 41·0 to 42·8, and that of the whole summer from 71·6 to73·4. In the New World, the division of heat between the seasons issuch, that, on the isothermal line of 58·1, the coldest month is 35·6,and that the thermometer sometimes sinks there even, during severaldays, from 14° to 10·4. The region of potable wines extends, inEurope, between the isothermal lines of 62·6 and 50°, which corre-spond to the latitudes of 36° and 48°. The cultivation of the vineextends, though with less advantage, even to countries whose annualtemperature descends to 48·2 and to 47·48; that of winter to 33·8,and that of summer to 66·2 and 68°. These meteorological condi- |381|tions are fulfilled in Europe as far as the parallel of 50°, and a littlebeyond it. In America, they do not exist farther north than 40°.They have begun, indeed, some years ago, to make a very good redwine to 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 temperature is32°, do not commence till on the isothermal lines of 48·2 and 50°, infrom 51° to 52° of latitude; while, in America, we find them alreadyon the isothermal lines of from 51·8 to 53·6, under from 40° to 41° oflatitude. If, instead of considering the natural inflexions of the isothermallines,—that is to say, those that propagate themselves progressively atgreat intervals of longitude,—we direct our attention to their partialinflexions, or to particular systems of climates occupying a small ex-tent of country, we shall still find the same variations in the divisionof the annual heat between the different seasons. These partial in-flexions are most remarkable: 1st. In the Crimea, where the climate of Odessa is contrasted withthat of the S.W. shores of the Chersonesus, sheltered by mountains,and fit for the cultivation of the olive and the orange-tree. 2dly. Along the Gulf of Genoa, from Toulon and the Hieres Islesto Nice and Bordighera, (Annales du Museum, tom. xi. p. 219,)where the small maritime palm-tree, chamœrops, grows wild, and wherethe date-tree is cultivated on a large scale, not to obtain its fruit, butthe palms or etiolated leaves. 3dly. In England, on the coast of Devonshire, where the port ofSalcombe has, on account of its temperate climate, been called theMontpellier of the North, and where (in South Hams) the myrtle, the camellia Japonica, the fuchsia coccinea, and the buddleia globosa, * pass the winter in the open ground, and without shelter. 4thly. In France, on the western coasts of Normandy and Brittany.In the department of Finisterre, the arbutus, the pomegranate-tree,the yucca gloriosa and aliofolia, the erica Mediterranea, the hortensia, the fuchsia, the dahlia, resist in open ground the inclemency of awinter which lasts scarcely fifteen or twenty days, and which succeedsto a summer by no means warm. During this short winter, the ther-mometer sometimes falls to 17·6. The sap ascends in the trees fromthe month of February; but it often freezes even in the middle ofMay. The lavatera arborea is found wild in the isle of Glenans; andopposite to this island, on the continent, the astragalus bajonensis andthe laurus nobilis. † From observations made in Britanny for twelve years, at St. Malo,at Nantes, and at Brest, the mean temperature of the peninsula appearsto be above 56·3. In the interior of France, where the land is not

---

* 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.† Bonnemaison, Geogr. Botan. du Depart. du Finisterre, (Journal de Botan. tom. iii. p. 118.)|382|much elevated above the sea, we must descend 3° of latitude in orderto find an annual temperature like this. It is known, from the researches of Arthur Young,* that, in spiteof the great rise of the two isothermal lines of 53·6 and 55·4 on thewestern coast of France, the lines of culture (those of the olive, andof the maize and vine,) have a direction† quite opposite, from S.W.to N.E. This phenomenon has been ascribed,‡ with reason, to thelow temperature of the summers along the coast; but no attempt hasbeen made to reduce to numerical expressions the ratios between theseasons in the interior and on the coast. In order to do this, I havechosen eight places, some of which lie under the same geographic pa-rallels, and others in the prolongation of the same isothermal line. Ihave compared the temperatures of winter, of summer, and of thewarmest months; for a summer of uniform heat excites less the forceof vegetation, than a great heat preceded by a cold season. The termsof comparison have been along the Atlantic; the coasts of Brittany,from St. Malo and St. Brieux to Vannes and Nantes; the sands ofOlonne; the Isle of Oleron; the embouchure of the Garonne andDax, in the department of the Landes: and, in the interior, corre-sponding to the same parallel, Chalons sur Marne, Paris, Chartres,Troyes, Poitiers, and Montauban.

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
Poitiera ..................	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 ..................	45·56	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

---

* 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 thedirection of the Great St. Bernard.‡ Decandolle, Flor. Franç. 3d edit. tom. ii. pl. viii. xi. Lequinio, Voy. dansle Jura, tom. ii. p. 84—91.|383| Farther south, from 44½° of lat., the comparisons become incor-rect, because France, locked between the Ocean and the Mediter-ranean, presents, along its last basin, in the fine region of the olives,a system of climate of a particular kind, and very different from thatof the western coast. These results are deduced from 127,000 observations, made withsixteen thermometers, of, no doubt, unequal accuracy. In suppos-ing, on the theory of probabilities, that, in such a number of observa-tions, the errors, in the construction and exposure of the instruments,and in the hours of observation, will in a great measure destroy oneanother, we may determine, by interpolation, either under the sameparallel or upon the same isothermal line, the mean winters and sum-mers of the interior and of the coast of France. This comparisongives—

			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
					Annual Temp.
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

As the isothermal lines rise again towards the western coasts ofFrance,—that is to say, as the mean temperature of the year becomesthere greater than under the same latitude in the interior of the coun-try,—we ought to expect that, in advancing from east to west underthe same parallel, the heat of the summers would not diminish. Butthe rising again of the isothermal lines, and the proximity of the sea,tend equally to increase the mildness of the winters; and each of thesetwo causes acts in an opposite manner upon the summers. If the di-vision of the heat between these seasons was equal in Brittany and inOrleannois, in the climate of the coast and the continental climates,we ought to find the winters and summers warmer in the same latitudealong the coast. In following the same isothermal lines, we readilyobserve, in the preceding table, that the winters are colder in the in-terior of the country, and the summers more temperate upon thecoasts. These observations confirm, in general, the popular opinionrespecting the climate of coasts; but, in recollecting the cultivationand the development of vegetation on the coasts and in the interior ofFrance, we should expect differences of temperature still more consi-derable. It is surprising that these differences between the winter andthe summer should not exceed 1·8, or nearly a quarter of the differ-ence between the mean temperature of the winters or the summers ofMontpellier and Paris. In speaking of the limits of the cultivation ofplants upon mountains, I shall explain the true cause of this apparentcontradiction. In the mean time it may be sufficient to remark, thatour meteorological instruments do not indicate the quantity of heat |384|which, in a clear and dry state of the air, the direct light produces inthe more or less coloured parenchyma of the leaves and fruits. In thesame mean temperature of the atmosphere, the development of vegeta-tion is retarded or accelerated according as the sky is foggy or serene,and according as the surface of the earth receives only a diffuse lightduring entire weeks, or is struck by the direct rays of the sun. Onthe state of the atmosphere, and the degree of the extinction of light,depend, in a great measure, those phenomena of vegetable life, thecontrasts of which surprise us in islands, in the interior of continents,in plains, and on the summit of mountains. If we neglect these pho-tometrical considerations, and do not appreciate the production ofheat in the interior of bodies, and the effect of nocturnal radiation ina clear or a cloudy sky, we shall have some difficulty in discovering,from the numerical ratios of the observed summer and winter tem-peratures of Paris and London, the causes of the striking differencewhich appears in France and England in the culture of the vine, thepeach, and other fruit-trees.* When we study the organic life of plants and animals, we must ex-amine all the stimuli or external agents which modify their vitalactions. The ratios of the mean temperatures of the months are notsufficient to characterize the climate. Its influence combines the si-multaneous action of all physical causes; and it depends on heat,humidity, light, the electrical tension of vapours, and the variablepressure of the atmosphere. It is the last cause which, on the tops ofmountains, modifies the perspiration of plants, and even increases theexhaling organs. In making known the empirical laws of the distri-bution of heat over the globe, as deducible from the thermometricalvariations of the air, we are far from considering these laws as theonly ones necessary to resolve all the problems of climate. Most ofthe phenomena of nature present two distinct parts,—one which maybe subjected to exact calculation, and another which cannot be reachedbut through the medium of induction and analogy.

---

* Young’s Travels in France, vol. ii. p. 195.|468| Continuation of our Abstract of Baron Humboldt’s Dissertation onIsothermal Lines, and the Distribution of Heat over the Globe. 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 and winter,and between that of the whole year and the warmest month. Fromthe parallel of Rome to that of Stockholm, and consequently betweenthe isothermal lines of 60·8° and 41°, the difference of the months ofApril and May is every where 10·8 or 12·6, and all the successivemonths are those which present the most rapid increase of tempera-ture. But, as in northern countries, (in Sweden, for example,) themonth of April is only 37·4, the 10·8 or 12·6 which the month of |469|May adds,* necessarily produces there a much greater effect on thedevelopment of vegetation than in the south of Europe, where themean temperature of April is from 53·6 to 55·4. It is from an ana-logous cause that, in passing from the shade to the sum, either in ourclimates in winter, or between the tropics on the back of the Cordil-leras, we are more affected by the difference of temperature than insummer and in the plains; though in both cases the thermometricaldifference is the same,—for example, from 5·4 to 7·2. Near thepolar circle, the increase of the vernal heat is not only more sensible,but it extends equally to the month of June. At Drontheim, thetemperatures of April and May, like those of May and June, differ not10·8 or 12·6, but 14·4 or 16·2. In distinguishing upon the same isothermal line the places whichapproach its concave or convex summits, in the same system of climatesin the northern and southern regions, we shall find,— 1st. That the increase of the vernal temperature is great, (from14·4 or 16·2, in the space of a month,) and equally prolonged, where-ever the division of the annual heat between the seasons is very un-equal, as in the north of Europe, and in the temperate part of theUnited States. 2dly. That the vernal increase is great, (at least above 9° or 10·8,)but little prolonged, in the temperate part of Europe. 3dly. That the increase of the vernal temperature is small, (scarcely7·2,) and equally prolonged, wherever there is an insular climate. 4thly. That in every system of climates, in the zones contained be-tween the same meridians, the vernal increase is smaller, and lessequally prolonged, in low than in high latitudes. The isothermal zone from 53·6 to 55·4 may serve as an example forconfirming these different modifications of spring. In Eastern Asia,near the concave summit, the differences of temperature between thefour months of March, April, May, and June, are very great, andvery equal, (15·7, 13·3, and 13·9.) In advancing westward towardsEurope, the isothermal line rises again; and, in the interior of thecountry, near the convex summit, the increase is still greater, but littleprolonged: that is to say, that; of the four months which succeed oneanother, there are only two whose difference rises to 13°; they are9·4, 13·3, 4·1. Farther west, on the coasts, the differences becomesmall and equal,—viz. 3·6, 6·5, 5·6. In crossing the Atlantic, weapproach the western concave summit of the isothermal line of 53·6.The increase of vernal temperature shows itself anew, and almost asgreat and as much prolonged, as near the Arctic concave summit.The differences of the four months are 10·4, 13·9, and 10·8. In thecurve of annual temperature, the spring and autumn mark the transi-tions from the minimum and the maximum. The increments are na-turally slower near the summits than in the intermediate part of thecurve. Here they are greater, and of longer continuance, in propor-

---

* 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 an-other differ near the summits of the annual curve only 1·41, while the differencesrise in antumn from 3·6 to 5·4, and in spring from 5·4 to 7·2.|470|tion to the difference of the extreme ordinates. The autumnal decreaseof temperature is less rapid than the vernal increase, because the sur-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 heat whichit has acquired. The following Table will show how uniform thelaws are which I have just established:

Names of Places.	Lat.	March.	April.	May.	June.	Differences ofTemperature of theFour Months.	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 ..................	59·54	41·4	57·0	70·3	84·2	15·7 13·3 13·9	54·9

|471| In all places whose mean temperature is below 62·6, the revival ofnature takes place in spring, in that month whose mean temperaturereaches 42·8 or 46·4. When a month rises to,

• 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.

At Rome, it is the month of March, at Paris the beginning of May,and at Upsal the beginning of June, that reaches the mean tempera-ture of 51·8. Near the hospice of St. Gothard, the birch cannotvegetate, as the warmest month of the year there scarcely reaches46·5. Barley, in order to be cultivated advantageously, requires,† during ninety days, a mean temperature of from 47·3 to 48·2. Byadding the mean temperatures of the months above 51·8,—that is, thetemperatures of those in which trees vegetate that lose their foliage,—we shall have a sufficiently exact mean of the strength and continuanceof vegetation. As we advance towards the north, vegetable life isconfined to a shorter interval. In the south of France there are 270days of the year in which the mean temperature exceeds 51·8; that isto say, the temperature which the birch requires to put forth its firstleaves. At St. Petersburg, the number of these days is only 120.These two cycles of vegetation, so unequal, have a mean temperaturewhich does not differ more than 5·4; and even this want of heat iscompensated by the effects of the direct light, which acts on the pa-renchyma of plants in proportion to the length of the days. If wecompare, in the following Table, Eastern Asia, Europe, and America,we shall discover, by the increase of heat during the cycle of vegeta-tion, the points where the isothermal lines have their concave summits.The exact knowledge of these cycles will throw more light on theproblem of agricultural geography, than the examination of the singletemperatures of summer. In the system of European climates, from Rome to Upsal, betweenthe isothermal lines of 59° and 41°, the warmest month adds from16·2 to 18° to the mean temperature of the year. Farther north, andalso in Eastern Asia and in America, where the isothermal lines bendtowards the equator, the increments are still more considerable.

---

* Cotte, Meteorologie, p. 448.—Wahlenberg, Flor. Lap. pl. 51.† Playfair, Edin. Trans. vol. v. p. 202.—Wahlenberg in Gilbert’s An-nalen, tom. xli. p. 282.|472|

Lines of Equal Heat.	Names ofPlaces.	Latitude.	MeanTemp.of theYear.	Sum of theMean Temp.of theMonths thatreach 51·8.	Numberof theseMonths.	MeanTemp. ofthe Dayswhichreach 51·8.	MeanTemp. oftheWarmestMonths.	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,	Petersburg,	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.

|473| As two hours of the day indicate the temperature of the whole day,there must also be two days of the year, or two decades, whose meantemperature is equal to that of the whole year. From the mean often observations, this temperature of the year is found at Buda inHungary, from the 15th to the 20th of April, and from the 18th tothe 23d of October. The ordinates of the other decades may be re-garded as functions of the mean ordinates. In considering the tem-peratures of entire months, we find that, to the isothermal line of35.6, the temperature of the month of October coincides (generallywithin a degree,) with that of the year. The following Table provesthat it is not the month of April, as Kirwan affirms, (Estimate, &c.p. 166,) that approaches nearest to the annual temperature. |Spaltenumbruch|

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
Clincinnati ....	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

|Spaltenumbruch|

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
Petersburg ....	38.8	39.0	37.0
Abo ..........	41.4	42.0	40.8
Drontheim ....	39.9	39.2	34.3
Uelo ..........	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

As travellers are seldom able to make observations for giving imme-diately the temperature of the whole year, it is useful to know theconstant ratios which exist in each system of climates, between thevernal and autumnal temperatures, and the annual temperature. The quantity of heat which any point of the globe receives, is muchmore equal during a long series of years than we would be led to be-lieve from the testimony of our sensations, and the variable product ofour harvests. In a given place, the number of days, during which theN.E. or S.W. winds blow, preserve a very constant ratio, because thedirection and the force of these winds, which bring warmer or colderair, depend upon general causes, —on the declination of the sun,—onthe configuration of the coast,—and on the lie of the neighbouringcontinent. It is less frequently a diminution in the mean temperaturethan an extraordinary change in the division of the heat between thedifferent months, which occasions bad harvests. By examining, be-tween the parallels of 47° and 49°, a series of good meteorological ob-servations, made during ten or twelve years, it appears that the annualtemperatures vary only from 1.8 to 2.7: those of winter, from 3.6 to5.4; those of the months of winter, from 9°. to 10.8. At Geneva, themean temperatures of twenty years were as follow:— |474| |Spaltenumbruch| |Spaltenumbruch|

Years.	Mean Temp.
1796,	49.3°
1797,	50.5
1798,	50.0
1799,	48·7
1800,	50.5
1801,	51.1
1802,	50.9
1803,	50.4
1804,	51.1
1805,	47.8
Years.	Mean Temp.
1806,	51.4°
1807,	49.3
1808,	46·9
1809,	48·9
1810,	51·1
1811,	51·6
1812,	47.8
1813,	48.6
1814,	48.2
1815,	50.0
Mean of twenty years,....	49.67°

If, in our climates, the thermometrical oscillations are a sixth partof the annual temperature, they do not amount to one twenty-fifthpart under the tropics. I have computed the thermometrical varia-tions, during eleven years, at Paris, for the whole year, the winter,the summer, the coldest month, the warmest month, and the monthwhich represents most accurately the annual mean temperature; andthe following are the results which I obtained:

Observations ofM. Bouvard.	Mean Temperature
	of theYear.	ofWinter.	ofSummer.	ofJanuary.	ofAugust.	ofOctober.
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	63.1	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

At Geneva, the mean temperatures of the summers were, from 1803to 1809,—

Years.	Mean Temp. of. 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

M. Arago has found that, in the two years 1815 and 1816, the lastof which was so destructive to the crops in a great part of France, thedifference of the mean annual temperature was only 2°, and that ofthe summer 3.2°. The summer of 1816, at Paris, was 59.9°,—4.7°below the mean of the former. From 1803 to 1813, the oscillationsround the mean did not go beyond —2.9°, and +3.4°. In comparing places which belong to the same system of climates, |475|though more than eighty leagues distant, the variations seem to bevery uniform, both in the annual temperature and that of the seasons,although the thermometrical quantities are not the same.

Years.	Paris.		Geneva.		Paris.		Geneva.		Paris.		Geneva.
	MeanAnnualTempe-rature.	Differencebetweenmean Ann.Temp. andthat for 12 years, 51.1.	MeanAnnualTempe-rature.	Differencebetweenmean Ann.Temp. andthat for 12 years, 49.6.	MeanTempe-rature ofWinter.	Differencewith themean WinterTemp. of 12 years, 38.7.	MeanTempe-rature ofWinter.	Differencewith themean WinterTemp. of 12 years, 34.9.	MeanTempe-rature ofSummer.	Differencewith themean Tem-perature ofSummer for 12 years, 64.6.	MeanTempe-rature ofSummer.	Differencewith theMean Tem-perature ofSummer for 12 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	65.5	— 1.4
1809	50.9	— 0.2	48.7	— 0.9	40.5	+ 1.8	35.1	+ 0.2	62.4	— 2.2	65.1	— 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

|554| Continuation of our Abstract of Baron Humboldt’s Dissertation onIsothermal Lines, and the Distribution of Heat over the Globe. ALL the ratios of temperature which we have hitherto fixed belongto that part of the lower strata of the atmosphere which restson the solid surface of the globe in the northern hemisphere. It nowremains for us to discuss the temperature of the southern hemisphere. The southern hemisphere receives the same quantity of light; but theaccumulation of heat in it is less, on account of the emission of theradiant heat which takes place during a long winter. This hemispherebeing also in a great measure covered with water, the pyramidal ex-tremities of the continents have there an irregular climate. Summersof a very low temperature are succeeded, as far as 50° of south lati-tude, by winters far from rigorous. The small quantity of land in thesouthern hemispheres,* contributes not only to equalize the seasons,but also to diminish absolutely the annual temperature of that part ofthe globe. There is reason to believe that this want of dry land wouldproduce an effect still more sensible, if the division of the continentswas as unequal in the equinoctial as in the temperate zones.† Theory and experience prove that the difference of temperaturebetween the two hemispheres cannot be great near the limit whichseparates them. The differences of the two hemispheres becomemore sensible in the warmest months.

Rio Janeiro.	Mean Temp.	Havannah.	Mean Temp.
June ..........	68.6°	December ......	71.8°
July ..........	70.2	January ........	70.2
January ......	79.2	July ............	83.3
February ......	80.6	August .........	83.8

---

* 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, andwithout the tropics as 13 to 1.|555| The division of the heat between the different parts of the yeargives a particular character to southern climates. In the southernhemisphere, on the isothermal lines of 46.4 and 50.0, we find summerswhich in our hemisphere belong only to the isothermal lines of 35.6and 40°. The mean temperature is not precisely known beyond 51°of S. latitude. Navigators do not frequent those regions when thesun is in the northern signs, and it would be wrong to judge of therigour of winter from the low temperature of the summer. The inequal temperature of the two hemispheres, which is less theeffect of the eccentricity of the earth’s orbit than of the unequal divi-sion of the continents, determines the limit between the N.E. andand S.E. trade-winds. But, as this limit is much more to the north ofthe equator in the Atlantic Ocean than in the South Sea, we mayconclude that, in a region between 130° and 150° of W. longitude,the difference of temperature between the two hemispheres is lessgreat than farther to the east in 20° or 50° of longitude. The low strata of the atmosphere which rest upon the aqueous sur-face of the globe, receive the influence of the temperature of thewaters. The sea radiates less absolute heat than continents; it coolsthe air upon the sea, by the effect of evaporation; it sends the parti-cles of water cooled and heavier towards the bottom; and it is heatedagain, or cooled, by the currents directed from the equator to thepoles, or by the mixture of the superior and inferior strata on thesides of banks. With respect to the temperature of the ocean, we must distinguishbetween four very different phenomena. 1st. The temperature of thewater at the surface corresponding to different latitudes, the ocean be-ing considered at rest, and destitute of shallows and currents. 2d.The decrease of heat in the superimposed strata of water. 3d. Theeffect of billows on the temperature of the surface water. 4th. Thetemperature of currents, which impel, with an acquired velocity, thewaters of our zone across the immoveable waters of another zone. Hitherto we have attended to the distribution of heat on the surfaceof the globe at the level of the sea. It only remains for us to considerthe variations of temperature in the higher regions of the atmosphere,and in the interior of the earth. The decrease of heat in the atmosphere depends on several causes,the principal of which, according to Laplace and Leslie,† is the pro-perty of the air to increase its capacity for heat by its rarefaction. Ifthe globe was not surrounded by a mixture of elastic and aëriformfluids, it would not be sensibly colder at the height of 8747 yards thanat the level of the sea. As each part of the globe radiates in every di-rection, the interior of a spherical envelope, which would rest on thetop of the highest mountains, would receive the same quantity of ra-diant heat as the lower strata of the atmosphere. The heat, it is true,will be spread over a surface a little greater; but the difference of tem-perature will be insensible, since the radius of the spherical envelopewill be to that of the earth as 1.001 to 1. Considering the earth as surrounded with an atmospherical fluid, itis obvious that the air heated at its surface will ascend, dilate itself,

---

† Essay on Heat and Moisture, p. 11.; and Geometry, p. 495.|556|and be cooled, either by dilatation or by a more free radiation acrossthe other strata that are equally rarefied. These are the ascendingand descending currents, which keep up the decreasing temperature ofthe atmosphere. In comparing towns situated on elevated plains with those which areplaced on the declivity of mountains, I have found for the first anaugmentation of temperature, which, on account of the nocturnal ra-diation, does not exceed from 2.7 to 4.14. The following are the results which I have obtained from exact datain the temperate zone, from the plains to 1000 metres of elevation.Every hundred metres of perpendicular height diminishes the meantemperature of the year, by the same quantity that a change of onedegree of latitude does in advancing towards the pole. If we compareonly the mean temperature of summer, the first 1000 metres are equiva-lent to 0.81 Fahr. From 40° to 50° of latitude, the mean heat of theplains of Europe decreases in Europe 12.6 of Fahr.; and this samedecrease of temperature takes place on the declivity of the Swiss Alpsfrom 0 to 1000 metres of elevation.

Differences of Latitude, Compared with Differences of Elevation.	MeanHeatof 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 latitude ....	53.60	68.00	51.80
b. At an elevation of 1000 metres ..	41.00	58.46	42.80

I shall now conclude this memoir by the enumeration of the mostimportant results which have been obtained by Baron Von Buch, M.Wahlenberg, and myself, on the distribution of heat in the interior ofthe earth, from the equator to 70° of N. latitude, and from the plainsto 3600 metres (11,808 feet) of elevation. The interior temperature of the earth is measured either by thetemperature of subterraneous excavations, or by that of springs.This kind of observation is very liable to error, if the traveller doesnot pay the most minute attention to local circumstances which arecapable of altering the results. The air, when cooled, accumulatesin caverns, which communicate with the atmosphere by perpendicularopenings. The humidity of rocks depresses the temperature by theeffect of evaporation. Caverns that have little depth are more or lesswarmed according to the colour, the density, and the moisture, of thestrata of stone in which nature has hollowed them. Springs indicatetoo low a temperature, if they descend rapidly from a considerableheight upon inclined strata. There are some under the torrid zoneand in our climate which do not vary in their temperature throughoutthe whole year more than half a degree, and there are others whichshow the mean temperature of the earth only by observing them every |557|month, and taking the mean of all the observations. From the polarcircle to the equator, and from the tops of mountains towards theplains, the progressive increase of the temperature of springs dimi-nishes with the mean temperature of the ambient air. The tempera-ture of the interior of the earth is, at |Spaltenumbruch|

Lat.	Temp.Fahr.
Vadso ....70°0′	35°96′
Berlin ..52 31	49 28

|Spaltenumbruch|

Lat.	Temp.Fahr.
Paris ....48°50′	53°6′
Cairo ....30 2	72 5

In equinoctial America, I have found it in the plains from 77° to78.8°. The following are examples of the decrease of temperature from theplains to the tops of mountains.

Zone of 30°—55°.	Lat.	Mean Temp.of Air,Fahr.	Temp. of theInterior ofthe Earth.
Cairo ............	30°02′	72.68°	72.50°
Natchez ........	31 28	64.76	64.94
Charlestown ....	33 00	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°.
Calscrona ......	56 06	46.04	47.30
Upsal ..........	59 51	41.90	43.70
Umeo ..........	63 50	33.26	37.22
Vadso ..........	70 00	29.66	35.96

When we consider what a large portion of the globe is covered withthe sea, and examine the temperature of the deepest waters, we areconstrained to admit that, in islands, along coasts, and perhaps evenin continents of small extent, the interior heat of the earth is modifiedby the proximity of the strata of rocks on which the waters of theocean rest. I have considered successively, in this memoir, the distribution ofheat,—1, at the surface of the globe; 2, on the declivity of moun-tains; 3, in the ocean; 4, in the interior of the earth. In explainingthe theory of isothermal lines and their inflexions, which determine thedifferent systems of climates, I have endeavoured to reduce the pheno-mena of temperature to empirical laws. These laws will appear muchmore simple when we shall have multiplied and rectified by degrees thenumerical elements which are the results of observation. In the following general Table of the distribution of heat, the tem-peratures are expressed in degrees of Fahrenheit; the longitudes arereckoned from east to west of the meridian of the observatory ofGreenwich. The mean temperatures of the seasons have been calcu-lated, so that those of the months of December, January, andFebruary, form the mean temperature of winter. An asterisk (*) isprefixed to those places whose mean temperatures have been most ac-curately determined, and in general by means of 8000 observations.The isothermal lines have a convex summit in Europe, and two concavesummits in Asia and Eastern America. |558| |559|

Isother-malBands.	Names of Places.	Position.			MeanTemp.of the 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. ofWarm. Month.	Mean Temp. ofColdest Month.
Isothermal Bands from32° to 41°.	Nain ................	57°08′	61°20′ W	0	26.42°	— 0.60°	23.90°	48.38°	33.44°	51.80°	—11.20°
	* Enontekies ..........	68 30	20 47 E	1356	26.96	+ 0.68	24.98	54.86	27.32	59.54	— 0.58
	Hospice de St. Gothard	46 30	8 23 E	6390	30.38	18.32	26.42	44.96	31.82	46.22	15.08
	North Cape ..........	71 00	25 50 E	0	32.00	23.72	29.66	43.34	32.08	46.58	22.10
	* Uleo ................	65 03	25 26 E	0	35.08	11.84	27.14	57.74	35.96	61.52	7.70
	* Umeo ................	63 50	20 16 E	0	33.26	12.92	38.80	54.86	33.44	62.60	11.48
	* St. Petersburg ........	59 56	30 19 E	0	38.84	17.06	38.12	62.06	38.66	65.66	8.60
	Drontheim ..........	63 24	10 22 E	0	39.92	23.72	35.24	61.24	40.10	64.94	19.58
	Moscow ............	55 45	37 32 E	970	40.10	10.78	44.06	67.10	38.30	70.52	6.08
	Abo ................	60 27	22 18 E	0	40.28	20.84	38.30	61.88	40.64	—	—
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
	* Stockholm ..........	59 20	18 03 E	0	42.26	23.52	38.30	61.88	43.16	64.04	22.82
	Quebec ..............	46 47	71 10 W	0	41.74	14.18	38.84	68.00	46.04	73.40	13.81
	Christiania ..........	59 55	10 48 E	0	42.08	28.78	39.02	62.60	41.18	66.74	28.41
	* Convent of Peyssenburg	47 47	10 34 E	3066	42.98	28·58	42.08	58.46	42.98	59.36	30.20
	* Copenhagen ..........	55 41	12 35 E	0	45.68	30.74	41.18	62.69	48.38	65.66	27.14
	* Kendal ..............	54 17	2 46 W	0	46.22	30.86	45.14	56.84	46.22	58.10	34.88
	Malonin Islands ......	51 25	59 59 W	0	46.94	39.56	46.58	53.06	48.46	55.76	37.40
	* Prague ..............	50 05	14 24 E	0	49.46	81.46	47.66	68.90	50.18	—	—
	Gottingen ............	51 32	9 53 E	456	46.94	30.38	44.24	64.76	48.74	66.38	29.66
	* Zurich ..............	47 22	8 32 E	1350	47.84	29.66	48.20	64.04	48.92	65.66	26.78
	* Edinburgh ..........	55 57	3 10 W	0	47.84	38.66	46.40	58.28	48.56	59.36	38.30
	Warsaw ............	52 14	21 02 E	0	48.56	28.76	47.48	69.08	49.46	70.34	27.14
	Coire ................	46 50	9 30 E	1876	48.92	32.36	50.00	63.32	50.36	64.58	29.48
	Dublin ..............	53 21	6 19 W	0*	49.10	39.20	47.30	59.54	50.00	61.16	35.42
	Berne ..............	46 05	7 26 E	1650	49.28	32.00	48.92	66.56	49.82	67.28	30.56
	* Geneva ..............	46 12	6 08 E	1080	49.28	34.70	47.66	64.94	50.00	66.56	34.16
	* Manheim ............	49 29	8 28 E	432	50.18	38.80	49.64	67.10	49.82	68.72	33.44
	Vienna ..............	48 12	16 22 E	420	50.54	32.72	51.26	69.26	50.54	70.52	26.60
Isothermal Bands from 50° to 59°.	* Clermont ............	45°46′	3°05′ E	1260	50.00	34.52	50.54	64.40	51.26	66.20	28.04
	* Buda ................	47 29	19 01 E	494	51.08	33.98	51.08	70.62	52.34	71.60	27.78
	Cambridge (U. S.) ....	42 25	71 03 W	0	50.36	33.98	47.66	70.70	49.82	72.86	29.64
	* Paris ................	48 50	2 20 E	222	51.08	38.66	49.28	64.58	51.44	65.30	36.14
	* London ..............	51 30	0 05 W	0	50.36	39.56	48.56	63.14	50.18	64.40	37.76
	Dunkirk ............	51 02	2 22 E	0	50.54	38.48	48.56	64.04	50.90	64.76	37.75
	Amsterdam ..........	52 22	4 50 E	0	51.62	36.86	51.62	65.84	51.62	66.92	35.42
	Brussels ............	50 50	4 22 E	0	51.80	36.68	53.24	66.20	51.08	67.28	35.60
	* Franeker ............	52 36	6 22 E	0	51.80	36.68	51.08	67.28	54.32	69.08	32.90
	Philadelphia ..........	39 56	75 16 W	0	53.42	32.18	51.44	73.94	56.48	77.00	32.72
	New York ..........	40 40	73 58 W	0	53.78	29.84	51.26	79.16	54.50	80.78	25.34
	* Cincinnati ............	39 06	82 40 W	510	53.78	32.90	54.14	72.86	54.86	74.30	30.20
	St. Malo ............	48 39	2 01 W	0	54.14	42.26	52.16	66.02	55.76	66.92	41.74
	Nantes ..............	47 13	1 32 W	0	54.68	40.46	54.50	68.54	55.58	70.52	39.02
	Pekin ..............	39 54	116 27 E	0	54.86	26.42	56.30	82.58	54.32	84.38	24.62
	* Milan ..............	45 28	9 11 E	390	55.76	36.32	56.12	73.04	56.84	74.66	36.14
	Bourdeaux ..........	45 50	0 34 W	0	56.48	42.08	56.48	70.88	56.30	73.04	41.00
IsothermalBands from59° to 63°.	Marseilles ............	43 17	5 22 E	0	59.00	45.50	57.56	72.50	60.08	74.66	44.42
	Montpellier ..........	43 36	3 52 E	0	59 36	44.06	56.66	75.74	60.98	78.08	42.08
	* Rome ..............	41 53	12 27 E	0	60.44	45.86	57.74	75.20	62.78	77.00	42.26
	Toulon .............	43 07	5 50 E	0	62.06	48.38	60.80	75.02	64.40	77.00	46.40
	Nangasacki ..........	32 45	129 55 E	0	60.80	39.38	57.56	82.94	64.22	86.90	37.40
	Natchez ............	31 28	90 30 W	180	64.76	48.56	65.48	79.16	66.02	79.70	46.94
Isother.Bandsfrom 68°to 77°.	* Funchal ..............	32 37	16 56 W	0	6°.54	61.40	65.84	72.50	72.32	75.56	64.04
	Algiers ..............	36 48	3 01 E	0	69.98	61.52	65.66	80.24	72.50	82.76	60.08
Isother.Bandsabove77°.	* Cairo ................	30 02	31 18 E	0	72.32	58.46	73.58	85.10	71.42	85.82	56.12
	* Vera Cruz ............	19 11	96 01 W	0	77.72	71.96	77.90	81.50	78.62	81.86	71.06
	* Havannah ............	23 10	82 13 W	0	78.08	71.24	78.98	83.30	78.98	83.84	69.98
	* Cumana ............	10 27	65 15 W	0	81.86	80.24	83.66	82.04	80.24	84.38	79.16