Digitale Ausgabe

The unequal distribution of heat over the globe is one of thosephenomena which has been long known as a general fact, butwhich cannot be exactly ascertained, with respect to its particularlaws, until we have more correct data furnished by observationand experiment. To furnish these data is the immediate objectof this paper; they are deduced from a great number of factswhich have not been published; and if they are not sufficient toenable us to form a correct theory, they may, at least, lay a foun-dation for it, and will be useful in pointing out to travellers thoseobjects to which they ought especially to direct their attention. The distribution of vegetables and of organized beings in generaldepends upon the circumstances that are connected with latitude,longitude, and elevation; and of these one of the most importantis atmospherical temperature. The means which the authorenjoyed of making observations, during his residence in SouthAmerica, have enabled him to establish some very valuable data,which could not have been obtained in any other situation, moreespecially those which require to be made at great heights above

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* Abridged from the third volume of the Memoirs of the Society of Arcueil.|178| the level of the ocean. The highest point in Europe where anyobservations have been made, is the Hospice de St. Gothard, atabout 6,400 feet above the sea; but in South America the townof Quito is about 9,000 feet, Huancavelica about 11,670 feet, andthe mine of Santa Barbara as much as 14,400 feet above the sea,or more than double that of St. Gothard. In order to comparethe results which were obtained in the equinoxial regions withthe mean heat of temperate climates, it was necessary to findout different situations, at intervals of 10° of latitude, but ondifferent meridians, the mean temperature of which had beenaccurately ascertained. These will form so many fixed points,through which the isothermal lines, or the lines of equal temper-ature, may pass. In collecting facts for ascertaining thesestations, comparatively few of the numerous thermometricalobservations that have been published could be employed. Manyof the observations contradict each other; in many cases we donot know under what circumstances they were made; and we arefrequently obliged to reject such as, in other respects, appearcorrect, because we are not acquainted with the absolute heightof the place at which they were made. This is remarkably thecase with almost the whole of Asia; and it is not a little singularthat, while there are more than 500 stations in the equinoxialdistrict of America, many of them mere villages, or even hamlets,the altitude of which has been exactly determined, we are igno-rant of the height of Bagdat, Aleppo, Ispahan, Delhi, and manyother large and ancient cities in the Old World. In comparingthe temperatures of different places, it is, however, quite neces-sary either that they should be upon the same level, or that aproper allowance should be made for any difference which theremay be in this respect. In the old continent the only good observations which can beemployed to form our calculations are limited by the parallelsof 30° and 70° of latitude, and by the meridians of 30° east and20° west longitude; the extreme points of which are, the islandof Madeira, Cairo, and Cape North; it comprises about \( \frac{1}{7} \) thecircumference of the globe from east to west. There are manycircumstances connected with Europe, partly depending uponits natural form and situation, and partly upon the state of itscivilization, which have given a peculiar character to its climate,different from that of other regions in the same latitude. But asthis has been the abode of men of science, they have consideredthe laws which regulate the temperature of that part of theworld as what are applicable to all the others. In this, however,they have fallen into some considerable errors, the causes andthe amount of which we must endeavour to discover and appre-ciate. It is not with the temperature of the atmosphere, andwith the magnetism of the globe, as with those phenomena which are determined by a single cause, and may be consideredas distinct from all disturbing causes. From their nature, they |179| both depend upon many local circumstances, such as the con-stitution of the soil, and the disposition of the radiating surfaceof the globe; and it frequently requires much judgment anddiscrimination to decide what circumstances are to be taken intoaccount, and what are not connected with the inquiry. Theobject is to ascertain the quantity of heat which every part ofthe globe receives annually, and which is of actual use to agri-culture and the well-being of the inhabitants; not what dependssolely upon the action of the sun, its height above the horizon, orthe extent of its semi-diurnal arcs. The temperature of a climatedepends both upon the action of the sun, and of various extrinsiccauses; among these may be enumerated the mixture of thetemperatures of different latitudes, produced by winds, the vicinityof the sea, the nature of the soil, the presence and peculiar formof mountains, and the existence of large tracts of snow or massesof ice. In distinguishing between the solar and the real climate, wemust remember that the local causes which modify the sun’saction are themselves only secondary causes, effects which themotion of this luminary produces in the atmosphere. Many ofthe local or disturbing causes are necessarily connected with thenature of heat, and are felt over every part of the globe. Theocean tends to equalize the temperature of all the differentregions by the mobility which necessarily belongs to it, and thecurrents of warm air which always flow from the equator to thepoles, tend to diminish the rigour of the countries of the north.In estimating the action of the sun alone on the earth, we musthave recourse to theory: this will not express the actual heightof the thermometer in different situations, but it will show therelations between the mean temperature of different regions.By comparing the results of the calculation, not to the meandeduced from observations made in different longitudes, but tothe mean temperature of a single point taken at the surface ofthe earth, we may proceed in our examination of what dependsupon the sun, and upon all the other influences, solar or notsolar, local, or such as extend to considerable distances. In thisway we shall be able to form an interesting comparison betweentheory and experience. For the first philosophical ideas upon the subject of solar heat,we are indebted to Halley. Marian afterwards extended ourknowledge of solar action; but he fell into some considerableerrors, which were rectified by Lambert, who instituted someimportant calculations, which, however, do not always accordwith actual experience, and which, indeed, depend almostentirely upon mathematical principles. After him, the subjectwas taken up by Mayer and by Kirwan; and they proceededmore upon observation, at least upon the method of endeavour-ing to approximate to a true system by collecting observations,and employing them to correct the theory. In speaking of the |180|authors who have added to our knowledge on the temperatureof the different parts of the earth, we must not omit to mentionCotte, who has collected a great number of documents; butthey are not reduced into any kind of method, and are not all ofequal authority. These considerations lead us to the conclusion that, in inves-tigating the distribution of temperature, it is important to distin-guish between the results which are deduced from observation,and those which are derived from theory. We must collect allthe authentic facts that can be obtained; and, after arrangingthem into regular order, we must submit them to what may betermed empirical laws. After having correctly ascertained themean temperature of certain places, we may trace on the globe isothermal lines, which thus exhibit to the eye the relation ofthese places to each other. In determining the mean temperatureof a particular spot, the old plan was to take the maximum andminimum temperature of the year, and to consider the middlenumber between them as the mean temperature; but this planis obviously incorrect. De la Hire seems to have been the firstwho attempted to pursue a different method, and one founded onmore just principles: observing the uniformity of the tempera-ture of the vaults that are attached to the observatory at Paris,he proposed as a general fact, that the temperature of vaults wasthe mean temperature of the climate.* The other method, thatof the maxima and minima, continued, however, to be generallyadopted; and, by multiplying the number of the observations, itwas rendered more correct, but still liable to inaccuracy. Someof the latest observers have noted the thermometer threetimes each day, and then taken the mean of these as denotingthe mean temperature of the day; others have adopted theplan of observing the thermometer at two periods in the day,which are considered as indicating the maximum and minimum—sun-rise, and two hours after noon; while others, again, havesatisfied themselves with observing the temperature at oneperiod only, which has been found, by previous experience, todenote the mean temperature. By comparing a great number of observations made between46° and 48° N. latitude, we find that at the hour of sun-set thetemperature is very nearly the mean of that at sun-rise and twohours after noon. When, besides noting the maximum andminimum, we take a middle observation, we shall fall into anerror, if we simply divide the sum of the observations by three,without attending to the duration of the particular temperatures,and the place which the middle observation occupies betweenthe extreme terms of the series. The middle observation shouldbe at least four or five hours from either of the others; but, uponthe whole, the two observations of the extreme temperatures

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* Mem. Acad. Sciences, 1719, p. 4.|181| will give us more correct results. Some very valuable observa-tions have been made by noticing the thermometer from hour tohour, at different seasons of the year, and in different latitudes,until we are able to fix upon a number which may indicate themean of the day. Serene and calm weather has been chosen onthese occasions, and the thermometer has been carefully exa-mined in this way, both in the observatory at Paris, and underthe equator. These observations have tended to confirm theopinion that has been mentioned above, that the temperature ofthe earth corresponds with the mean temperature of the atmo-sphere, the disturbing causes nearly counteracting each other.In expressing the results of the observations on mean tempera-tures that have been made in various situations, it is convenientnot to employ the numbers that are derived from any parti-cular scale, but to consider the equator as the standard to whichall the rest are to be referred, and to denote them all by numberswhich have an arithmetical relation to it. Having now ascertained the method of taking mean tempera-tures, and of reducing them to a general expression, we mayproceed to examine the form of some of the isothermal lines. Ithas been long known that the temperatures are not the same inthe same parallels, especially those in Europe and in America;but, from the facts that will be stated, we shall find that thisdifference is not so great as has been imagined. By construct-ing a table, in which we compare the mean temperature andthe latitude of different places in the continents of Europe andAmerica, we learn the amount of this difference, and we deducefrom this the number of degrees of latitude which we must gonorthward in Europe in order to arrive at the same annual mean.From this train of observations, we find that the isothermal line,or band, which is considered as 32°,* passes between Ulea, inLapland, latitude 66° 68′, and Table Bay, in Labrador, latitude54°. The isothermal line, or band, of 41°, passes near Stockholm,latitude 60°, and St. George’s Bay, in Newfoundland, latitude48°. The isothermal line, or band, of 50°, passes through Bel-gium, latitude 51°, and near Boston, latitude 42° 30′. Theisothermal line, or band, of 59°, passes between Rome and Flo-rence, latitude 43°, and near Raleigh, in South Carolina, latitude36°. The direction of these lines of equal temperature gives thefollowing differences between the west of Europe and the east ofAmerica:

Latitude.	Mean of West of Europe.	Mean of East of America.	Differences.
30° ..........	70·1° ..........	66·8° ..........	3·3
40 ..........	63·1 ..........	54·5 ..........	8·6
50 ..........	50·8 ..........	37·9 ..........	12·9
60 ..........	40·0 ..........	24·0 ..........	16·0

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* The thermometrical numbers are all reduced from the centigrade scale to thatof Fahrenheit. In the original, the numbers on the centigrade scale are, 0°, 5°,10°, 15°, respectively.|182| In advancing from the equator towards the north pole, themean temperatures become less than that of the equator in thefollowing proportion:

Lat.	Temp.	Temp.
From 0°—20°	in the old contin. 35·6°	in the new 35·6°
20 —30	............... 39·2	........ 42·8
30 —40	............... 39·2	........ 44·6
40 —50	............... 44·6	........ 48·2
50 —60	............... 41·8	....... 45·1
0 —60	............... 72·2	........ 88·0

Having traced the isothermal belts from Europe to the pro-vinces of the New World, the next object will be to observe themin North America itself. There are two chains of mountains inthis continent—the Alleghanys, and the Rocky Mountains; thefirst running N.E. and S.W., the latter N.W. and S.E., makingnearly equal angles with the meridian, and enclosing the vastplains of Louisiana, Tennesee, and the state of Ohio. This coun-try possesses a milder climate than the parallel latitudes in theAtlantic States, the winters being less severe, and the summersless hot; so that the isothermal lines remain parallel, or nearlyparallel, to the equator, from the coast of the Atlantic to the eastof the Mississipi, and the Misoury. Beyond the Rocky Mountains the climate is still milder; in New California, and along thenorthern parts of the western side of the continent, the tempera-ture appears to be very nearly the same with what it is in similarlatitudes on the western side of Europe. The isothermal lineswill, therefore, be bent upwards in this part. When we pass from the west of Europe eastward, the iso-thermal lines are again curved downwards; but the few accurateobservations which we possess render it very difficult to fix theexact line; of the general fact, however, there is no doubt. Wehave hitherto found that, towards the north, the isothermal linesare neither parallel to the equator nor parallel to each other; andas the curve is the greatest in Asia and in America between 80°west and 100° east longitude, it might be supposed that thetorrid zone of this part commences to the south of the tropic ofCancer, or that its heat is less intense. This, however, doesnot appear to be the case; as we approach to the line, belowthe parallel of 30°, the isothermal lines gradually become parallelto themselves and to the equator. For some time the old conti-nent was thought to be warmer between the tropics than thenew; but more correct observations have shown that this is notthe case. The mean temperature of the equator may be fixed at81·2.° The distribution of the temperature through the different partsof the year differs in the same isothermal line; this is the casewith respect both to the old and new continents; in the former |183| a few months are warmer than in the latter; as, for example, theheats in Madras are greater than those in Cumana. In the tem-perate zone it has been long known that the cold of the winteraugments in a more rapid progression than the heat of thesummer decreases; it is also known that the climate of islands,and the sea-coast, is milder than the interior of continents; it is,therefore, an important object to compare the mean temperaturesof the three winter and the three summer months, at differentlatitudes, and to observe how the curves of the isothermal linesmodify these relations. By comparing together a tract on thewest with one on the east side of the Atlantic, extending acrossthe different isothermal lines, we find that the difference betweenthe two seasons increases more in the transatlantic than in thecisatlantic district. But in both the districts the division ofthe temperature between the winter and summer months is such,that upon the line of 32° the difference is nearly double what itis upon the line of 68°. In tracing the same isothermal line from west to east, in orderto observe the difference between the winters and the summers,we find that the difference is less near the convex summits of thelines than near the concave summits. The same causes whichtend to raise up the lines towards the pole also tend to equalizethe seasons. Europe may be regarded altogether as the westernpart of a great continent, and subject to all those influenceswhich make the western sides of all continents warmer than theeastern. The same difference that we observe in the two sidesof the Atlantic exists on the two sides of the Pacific; in thenorth of China the extremes of the seasons are much more feltthan in the same latitudes in New California, and at the mouth ofthe Columbia. On the eastern side of North America we havethe same extremes as in China; New York has the summer ofRome and the winter of Copenhagen; Quebec has the summerof Paris and the winter of Petersburgh. And, in the same wayin Pekin, which has the mean temperature of Britain, the heatsof summer are greater than those at Cairo, and the cold of winteras severe as that at Upsal. This analogy between the easterncoasts of Asia and of America sufficiently proves that the ine-qualities of the seasons depend upon the prolongation andenlargement of the continents towards the pole, and upon thefrequency of the N. W. winds, and not upon the proximity of anyelevated tracts of country. |184|

TABLE I.

Places.	March.	April.	May.	June.	Differences of temp. ofthe four months.	M. temp.of year.
First Group. Concave summits inAmerica.
Natchez, lat. 31° 28′	58·0°	66·2°	72·6°	79·2°	8·2° 6·4° 6·6°	64·8°
Williamsburg 37 18	46·4	61·2	66·6	77·8	14·8 5·4 11·2	58·1
Cincinnati ... 39 0	43·7	57·4	61·2	70·8	13·7 3·8 9·4	53·8
Philadelphia . 39 56	44·0	53·6	61·8	72·4	9·6 8·2 10·6	53·6
New York ... 40 40	38·6	49·1	65·8	82·2	10·5 16·7 16·4	53·8
Cambridge ... 42 25	34·6	45·5	56·8	70·2	10·9 11·3 13·4	50·4
Quebec ...... 46 47	23·0	39·6	54·6	63·8	16·6 15·0 9·2	41·8
Nain ........ 57 0	6·8	27·5	37·0	43·8	20·7 9·5 6·8	26·4
Second Group. Convex summits in Eu-rope.(A) Climate of the con-tinent.
Rome ....... 41° 53′	50·4	55·4	67·0	72·4	5·0 11·6 5·4	60·4
Milan ....... 45 28	47·8	51·0	65·2	70·6	3·2 14·2 5·2	55·8
Geneva ...... 46 12	39·6	45·6	58·1	62·2	6·0 12·5 4·1	49·2
Buda ........ 47 29	38·3	49·1	64·8	68·4	10·3 15·7 3·6	60·0
Paris ........ 48 50	42·2	48·2	60·0	64·4	6·0 11·8 4·4	60·0
Gottingen .... 51 32	34·2	44·1	57·8	63·2	9·9 13·7 5·4	46·7
Upsal ....... 59 61	29·4	39·8	48·8	58·0	10·4 9·0 9·2	41·9
Petersburgh .. 59 56	27·5	36·9	52·2	59·4	9·4 15·3 7·2	38·8
Umea ....... 63 50	23·0	34·2	43·7	55·0	11·2 9·5 11·3	33·2
Ulea ........ 65 0	14·0	26·0	41·0	55·0	12·0 15·0 14·0	35·0
Enontekies .. 68 30	11·4	26·6	36·5	49·4	15·2 9·9 12·9	27·0
(B) Climate of the coast.
Nantes ...... 47° 13′	50·0	53·6	60·0	65·6	3·6 13·6 5·6	54·6
London ...... 51 30	44·2	49·8	56·4	64·2	5·6 6·6 7·8	51·6
Dublin ...... 53 21	41·9	45·8	51·8	55·6	3·9 6·0 3·8	48·4
Edinburgh ... 57 57	41·4	47·3	50·6	57·2	5·9 3·3 6·6	47·8
Cape North .. 71 0	24·8	30·0	34·0	40·1	5·2 4·0 6·1	32·0
Third Group.Concave summit of Asia.
Pekin ....... 39° 54′	41·4	57·0	70·4	84·2	15·6 23·4 13·8	54·8

TABLE II.

Places.	Cisatlantic band, longitude29° E. 20° W.				Places.	Transatlantic band, longi-tude 67° E. 97° W.
	Lat.	Mean temp. of the				Lat.	Mean temp. of the
		Year.	Win-ter.	Sum-mer.			Year.	Win-ter.	Sum-mer.
(Pondicherry)	11° 35′	85·4°	77·0°	90·8°	Cumana .....	10° 27′	81·6°	81·3°	83·3°
Cairo .......	30 2	72·6	57·6	84·6	Havannah ...	23 10	77·7	80·4	79·9
Funchal .....	32 37	68·4	63·8	72·5	Natchez .....	31 28	64·8	48·6	79·0
Rome .......	41 55	60·1	45·8	75·2	Cincinnati ...	39 6	53·6	32·9	73·0
Bourdeaux ...	44 50	56·5	42·0	70·9	Philadelphia .	39 56	53·1	32·2	73·8
Paris .......	48 50	51·8	38·3	66·2	New York ..	40 40	53·9	30·0	79·0
Copenhagen .	55 41	45·6	31·0	62·6	Cambridge ...	42 25	50·4	34·0	70·4
Stockholm ...	59 20	42·2	26·0	61·8	Quebec ......	46 47	41·6	15·0	68·0
Drontheim ...	63 24	39·7	24·0	61·3	Nain ........	57 10	26·4	– 0·4	48·4
Umea .......	63 50	31·0	13·4	54·4	Fort-Churchill	59 2	25·5	6·8	52·0

|185| The following table shows how the annual heat is dividedbetween the two seasons of winter and summer in all the dif-ferent parts of the temperate zone. The observations are tracedalong the isothermal lines from W. to E., and those are preferredwhich are situated nearest to the most curved parts of the lines;the longitudes are taken from the meridian of Paris:

		Mean temperature of
	Isothermal lines from 32° to 68°.	Winter.	Summ.
* Isothermallines of 68°.	Long. 84° 30′ W.; lat. 29° 30′. (Florida). ........	53·6 ..	80·6
	Long. 19° 19′ W.; lat. 32° 37′ (Madeira)..........	63·6 ..	72·0
	Long. 0° 40′ E.; lat. 36° 48′ (N. of Africa). ......	59·0 ..	80·6
Isoth. line of63·5°.	Long. 92° W; lat. 32° 30′ (Mississipi).............	46·4 ..	77·0
	Long. 11° 51′ E.; lat. 40° 50′ (Italy). ............	50·0 ..	77·0
Isoth. line of59°.	Long. 86° 30′ W.; lat. 35° 30′ (Basin of the Ohio).	39·2 ..	78·4
	Long. 1° 2′ E.; lat. 43° 30′ (South of France). ....	44·6 ..	75·2
Isoth. line of54·5°.	Long. 87° W.; lat. 38° 30′ (Amer. W. of the Alleg-hanys)........................................	34·7 ..	75·2
	Long. 76° 30′ W.; lat. 40° (Amer. E. of the Alleg-hanys)........................................	32·7 ..	77·0
	Long. 3° 52′ W.; lat. 47° 10′ (West of France).....	41·0 ..	68·0
	Long. 7° E.; lat. 45° 30′ (Lombardy). ............	34·7 ..	73·4
	Long. 114° E.; lat. 40° (Eastern Asia)............	26·6 ..	82·4
Isoth. line of50°.	Long. 86° 40′ W.; lat. 41° 20′ (Amer. W. of theAlleghanys)...................................	31·1 ..	71·6
	Long. 73° 30′ W.; lat. 40° (Amer. E. of the Alleg-hanys)........................................	30·2 ..	73·4
	Long. 9° W.; lat. 52° 30′ (Ireland). ..............	39·2 ..	59·8
	Long. 3° W.; lat. 53° 30′ (England)..... ........	37·4 ..	62·6
	Long. 0°; lat. 51° (Belgium). ....................	36·5 ..	61·5
	Long. 16° 40′ E.; lat. 47° 30′ (Hungary)..........	31·1 ..	69·8
	Long. 114° E.; lat. 40° (Eastern Asia)............	23·0 ..	78·8
Isoth. line of45·5°.	Long. 23° 20′ W.; lat. 44° 42′ (Amer. E. of the Alleg-hanys)........................................	23·9 ..	71·6
	Long. 4° 30′ W.; lat. 57° (Scotland)..............	36·0 ..	56·4
	Long. 10° 15′ E.; lat. 55° 40′ (Denmark)..........	31·3 ..	62·6
	Long. 19° E.; lat. 53° 5′ (Poland)................	28·0 ..	66·2
Isoth. line of41°.	Long. 73° 30′ W.; lat. 47° (Canada). ............	14·0 ..	68·0
	Long. 7° E.; lat. 62° 45′ (Western Norway).......	24·8 ..	62·6
	Long. 15° E.; lat. 60° 30′ (Sweden)...............	24·8 ..	60·8
	Long. 22° E.; lat. 60° (Finland).................	23·0 ..	63·5
	Long. 34° E.; lat. 58° 30′ (Centre of Russia)......	13·0 ..	68·0
Isoth. line of36·5°.	Long. 74° W.; lat. 50° (Canada).................	6·8 ..	60·8
	Long. 15° 45′ E.; lat. 62° 30′ (W. coast of gulf ofBothnia).....................................	17·6 ..	57·2
	Long. 20° E.; lat. 62° 50′ (E. coast of ditto)......	16·7 ..	59·0
Isoth. line of32°.	Long. 60° W.; lat. 53° (Labrador). .............	3·2 ..	51·8
	Long. 17° 30′ E.; lat. 65° (Sweden)..............	11·3 ..	53·6
	Long. 23° E.; lat. 71° (Northern part of Norway).	— ..	45·7

We may perceive from this table that the inequality of thewinters on the same isothermal line increases as the annualheat diminishes, from Algiers to Holland, and from Florida toPennsylvania. If, instead of observing the most severe winterwhich is found in every climate, we trace the lines of similarwinter temperatures, which we may style isocheimal lines; these,so far from coinciding with the isothermal lines, oscillate roundthem, and connect situations that are placed upon different

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* These numbers, expressing the isothermal lines on the centigrade scale, are,20°, 17\( \frac{1}{2} \)°, 15°, 12\( \frac{1}{2} \)°, 10°, 7\( \frac{1}{2} \)°, 5°, 2\( \frac{1}{2} \)°, 0°.|186|isothermal lines. For example, in Belgium (geo. lat. 52°, isoth.lat. 51·8°), and even in Scotland (geo. lat. 57°, isoth lat, 45·5°),the winters are more mild than at Milan (geo. lat. 45° 28′, isoth.lat. 57·7°). Ireland presents one of the most remarkable ex-amples of the combination of very mild winters with cold sum-mers; the mean temperature in Hungary for the month ofAugust is 71·6°, while in Dublin it is only 60·8°. These, andmany other instances which might be adduced, prove that theisocheimal lines vary much more from the terrestrial parallels thanthe isothermal lines; in the climates of Europe the latitude oftwo places, which have the same annual temperature, never differsmore than 8° or 9°, while there are places that have the same winter temperature that differ in latitude 18° or 19°. The lines of equal summer heat, the isothermal curves, as wemay style them, follow an exactly contrary direction to the iso-cheimal. We find the same summer heat at Moscow and at themouth of the Loire, although the former is 11° further north than thelatter; a circumstance which is attributed to the radiation of theearth in an extensive continent, without any considerable moun-tains. With respect to the relation which subsists between thetemperature of winter and spring in different climates, it follows,from what has been stated above, that the increase of vernaltemperature is considerable, and likewise much protracted,wherever the distribution of the annual temperature among thedifferent seasons is very unequal, as in the north of Europe, andthe more temperate part of the United States; that the vernalincrease is great, but short, in the more temperate parts ofEurope; that it is small, but protracted, in islands; and that inthe different bands of climate enclosed between the same meri-dians, the vernal increase is smaller, and less protracted, in lowthan in high latitudes. Many very important conclusions arededuced from these facts respecting the effects of differentclimates on the cultivation of various kinds of plants, dependingpartly upon the absolute heat and cold of the summer and winterrespectively, partly upon their relation to each other, and partlyupon the transition from one season to the other. The southern hemisphere differs considerably from thenorthern; it is certainly colder; but the degree of differencebetween them has been very differently rated. The coldness ofthe southern hemisphere has generally been ascribed to the sunbeing a shorter space of time below than above the equator; butit probably depends more upon the greater proportion of ocean,which gives to the southern temperate zone a climate approach-ing to that of a collection of islands; there is, therefore, a lessaccumulation of heat during the summer, and a less radiationfrom the land, in proportion to its less extent; there is, conse-quently, a less current of warm air from the equator towards thesouth pole, which permits the ice to accumulate more round it.Near the equator, and indeed through the whole of the torridzone, the temperature of the two hemispheres appears to be |187|the same; but the difference begins to be felt in the Atlanticabout the 22° of latitude; and there is a considerable differencebetween the mean temperature of Rio Janeiro and Havannah,although they are both equally distant from the equator, theformer being 74·5°, the latter 76·4°. The southern climates gene-rally differ from those of the north in respect to the distributionof the temperature through the different parts of the year. Inthe southern hemisphere, under the isothermal lines of 46° and50°, we find summers which, in our hemisphere, belong to thelines of 35·5° and 41°. We are not accurately acquainted withthe mean temperature of any place above 50° of south latitude;but there is every reason for supposing that it differs considerablyfrom the same degree north. In estimating the temperature of the ocean there are fourcircumstances particularly to be attended to; 1. The temperatureof the water at the surface, corresponding to the different lati-tudes, supposing it to be at rest, without either shallows orcurrents; 2. The decrease of heat in the strata of water whichrest upon each other; 3. The effect of shallows, or banks, uponthe temperature of the surface water; 4. The temperature of thecurrents which mix together the waters of different zones. Thewater of the ocean is said to be the warmest between 5° 45′ N.and 6° 15′ S.; it has been found, by different observers, to befrom 82·5° to 84·5°; the temperature of the ocean in this partis from 4° to 6° higher than the temperature of the air whichreposes upon it. As we advance towards the poles, the influenceof the seasons upon the temperature of the surface of the seabecomes very sensible; but as a great mass of water follows thechanges of the temperature of the air very slowly, the means ofthe months in the ocean and in the air do not correspond. To complete the subject of temperature, we have still to con-sider its variations in the different regions of the atmosphere,and in the interior of the earth; but our remarks have beenalready extended to so great a length, that we shall not, atpresent, enter upon these topics.

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Isothermal Bands, and Distribution of Heat over the Globe. The temperatures are expressed in degrees of Fahrenheit’sthermometer; the longitudes are counted from east to west,from the first meridian of the observatory of Paris. The meantemperature of the seasons have been calculated so that themonths of December, January, and February, form the meantemperature of the winter. The mark * is prefixed to thoseplaces the mean temperatures of which have been determinedwith the most precision, generally by a mean of 8000 observa-tions. The isothermal curves having a concave summit inEurope, and two convex summits in Asia and Eastern America,the climate is denoted to which the individual places belong: |188| |189|

Isothermalbands.	Names of theplaces.	Position in			Meantemp. ofthe year.	Distribution of Heat in the different Seasons.				Maximum and Minimum.
		Latitude.	Longitude.	Height infeet.		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′	63° 40′ W	0	26·8°	– 0·4°	23·7°	48·4°	33·4°	51·8°	– 11·2° 1
	* Enontekies ....	68 30	18 27 E	1356	27·0	0·4	25·0	54·8	27·4	59·6	– 0·6 2
	Hospice de St.Gothard...	46 30	6 3 E	6390	30·4	18·4	26·4	45·0	31·8	46·2	15·0 3
	North Cape ....	71 0	23 30 E	0	32·0	23·8	29·4	43·2	32·2	50·2	22·1 4
	* Ulea ..........	65 3	23 6 E	0	33·0	11·8	27·2	57·8	36·0	61·6	7·7 5
	* Umea..........	63 50	17 56 E	0	33·2	13·0	33·8	54·8	33·4	62·6	11·4 6
	* Petersburg ....	59 56	27 59 E	0	38·8	17·0	38·2	62·0	38·6	65·6	8·6 7
	Drontheim.....	63 24	8 2 E	0	40·0	23·8	35·2	61·4	40·1	65·0	19·8 8
	Moscow. ......	55 45	35 12 E	970	40·2	10·8	44·0	67·1	38·3	70·6	6·0 9
	Abo. ..........	60 27	19 58 E	0	40·4	20·8	38·3	61·8	40·6	—	— 10
Isothermal bands from 41° to 50°.	* Upsal . ........	59 51	15 18 E	0	42·0	25·0	40·0	60·2	42·8	62·4	22·4 11
	* Stockholm .....	59 20	15 43 E	0	42·2	25·6	38·3	61·8	43·2	64·0	22·8 12
	Quebec ........	46 47	73 30 W	0	41·8	14·2	35·9	68·0	46·0	73·4	13·8 13
	Christiana.....	59 55	8 28 E	0	42·8	28·8	40·1	62·6	41·2	66·8	28·8 14
	* Convent ofPeyssenburg	47 47	8 14 E	3066	43·0	28·6	42·0	58·4	43·0	59·4	30·2 15
	* Copenhagen....	55 41	10 15 E	0	45·6	30·8	41·2	62·6	48·4	65·0	27·2 16
	* Kendal ........	54 17	5 6 W	0	46·2	36·8	45·2	56·8	46·2	58·1	34·8 17
	Malouin Is-lands ......	51 25	62 19 W	0	47·0	39·6	46·6	53·0	48·4	55·8	37·4 18
	* Prague ........	50 5	12 4 E	0	49·4	31·4	47·6	68·9	50·2	—	— 19
	Gottingen ......	51 32	7 33 E	456	47·0	30·4	44·2	64·8	48·6	66·4	33·2 20
	* Zurich ........	47 22	6 12 E	1350	47·8	29·6	48·2	64·0	48·8	65·7	26·8 21
	* Edinburgh. ....	55 57	5 30 W	0	47·8	38·6	46·4	58·2	48·4	59·4	38·3 22
	Warsaw. ......	52 14	18 42 E	0	48·6	27·8	47·4	69·0	49·4	70·4	27·2 23
	* Coire .........	46 50	7 10 E	1876	49·0	32·4	55·4	63·4	50·4	64·6	29·6 24
	Dublin ........	53 21	8 39 W	0	49·2	39·2	47·3	59·6	50·0	61·0	35·4 25
	Berne. ........	46 5	5 6 E	1650	49·3	32·0	49·0	66·6	49·8	67·2	30·6 26
	* Geneva ........	46 12	3 48 E	1080	49·3	34·9	47·6	65·0	50·0	66·6	34·2 27
	* Manheim ......	49 29	6 8 E	432	50·2	33·8	49·6	67·1	49·8	68·8	33·4 28
	Vienna ........	48 12	14 2	420	50·6	32·8	51·2	69·2	50·6	70·6	26·6 29
Isothermal band from 50° to 59°.	* Clermont ......	45 46	0 4 5	1260	50·0	34·7	50·6	64·4	51·2	66·2	28·0 30
	* Buda ..........	47 29	16 41	494	51·0	31·0	51·0	63·2	52·4	71·6	27·6 31
	Cambridge(U.S)	42 25	73 23 W	0	50·4	34·0	47·6	64·4	49·8	72·8	29·8 32
	* Paris ..........	48 50	0 0	222	51·0	38·6	49·2	64·6	51·4	65·3	36·0 33
	* London ........	51 30	2 25 W	0	50·4	39·6	48·6	63·2	50·2	64·4	37·8 34
	Dunkirk ......	51 2	0 2 E	0	50·6	38·4	48·6	63·8	50·9	64·8	37·8 35
	Amsterdam ....	52 22	2 30 E	0	51·6	36·8	51·6	65·8	51·6	67·0	35·4 36
	Brussels. ......	50 50	2 2 E	0	51·8	36·6	53·2	66·2	51·0	67·4	35·6 37
	* Franeker ......	52 36	4 2 E	0	51·8	36·6	51·0	67·2	54·4	69·0	32·9 38
	Philadelphia. ..	39 56	77 36 W	0	53·4	32·2	51·4	74·0	56·6	77·0	32·7 39
	New York. ....	40 40	76 18 W	0	53·8	29·8	51·2	79·2	54·6	80·6	25·4 40
	* Cinninnati. ....	39 6	85 0 W	510	53·8	32·9	54·4	72·8	54·4	74·3	30·2 41
	St. Malo. ......	48 39	4 21 W	0	54·4	42·2	52·2	66·0	55·8	67·0	41·8 42
	Nantes ........	47 13	3 52 W	0	55·0	40·4	54·5	68·6	55·6	70·6	38·0 43
	Pekin. ........	39 54	114 7 E	0	55·2	26·8	56·3	82·6	54·2	84·4	39·4 44
	* Milan. ........	45 28	6 51 E	390	55·8	36·4	56·1	73·0	56·8	74·6	36·2 45
	Bourdeaux ....	44 50	2 54 W	0	56·4	42·0	56·8	70·8	56·3	72·8	41·0 46
Isothermalband from 59°to 63°.	Marseilles .....	43 17	3 2 E	0	59·0	45·5	57·6	72·5	60·0	74·6	44·4 47
	Montpelier ....	43 36	1 32 E	0	59·4	44·0	57·0	75·8	61·0	78·2	42·0 48
	* Rome. ........	41 53	10 7 E	0	60·4	45·8	57·8	75·2	62·8	77·0	42·2 49
	Toulon........	43 7	3 30 E	0	62·0	48·4	60·8	74·8	64·4	77·0	46·4 50
	Nangasachi ....	32 45	127 35 E	0	60·8	39·4	57·6	83·0	64·2	86·9	37·4 51
	* Natchez. ......	31 28	93 50 W	180	64·8	48·6	65·4	79·2	65·8	79·7	47·0 52
Isotherm-al bandfrom 68°to 77°.	* Funchal. ......	32 37	19 16 W	0	68·6	64·8	65·8	72·5	72·4	75·6	64·2 53
	Algiers .......	36 48	0 41 E	0	70·0	61·4	65·6	80·2	72·5	82·8	60·0 54
Isotherm-al bandsabove77°.	* Cairo. ........	30 2	28 58 E	0	72·4	58·4	73·6	85·1	70·5	85·8	55·8 55
	* Veracruz......	19 11	98 21 W	0	77·8	72·0	77·9	81·5	78·6	81·5	71·0 56
	* Havannah. ....	23 10	84 33 W	0	78·2	71·2	79·0	83·3	79·0	84·0	70·0 57
	* Cumana. ......	10 27	67 35 W	0	81·8	80·2	83·6	82·0	79·6	84·4	79·2 58

|190| 1 Coast of Labrador. Two years of observations. Floatingice towards the east. A transatlantic climate. Mean tempera-ture of Oct. about 34·6°; Nov. 26·6°. 2 Centre of Lapland. A European climate. Fine vegetation.June, 49·4°; July, 59·6°; Aug. 56°; Sept. 41·8°; Oct. 27.5°;Nov. 12·4°. Inland situation. Specimen of a continentalclimate. 3 Eleven years of observations, calculated afresh in decads byWahlenberg. Thermometer verified by Saussure. Mean tem-perature of seven months of the year below 32°. Winds blowfrom Italy in the winter. Minimum observed in the winter– 0·4°; in Aug. at noon, in the shade, maximum 54·5°; thenights in Aug. frequently from 33·8° to 29·3°; the mean tem-perature of Oct. 29·3° represents that of the whole year; at theCol de Geant, 10,598 feet high, the mean temperature of Julyis 36·5°. We find 32° to be the mean temperature in Europe,in 45° of latitude, at 5,400 feet high; at the parallel of theCanaries, at 12,300 feet; in the Andes, under the Equator, at16,500 feet. 4 Buch, Voy. en Norw. ii. 416. Specimen of the climate ofthe islands and coasts in the north of Europe. April, 30°; May,33·8°; Oct. 32°; Nov. 25·8°. At Alten, lat. 70°; mean temper-ature of July, 63·5°; a continental climate. 5 Finland, eastern coast. May, 40·8°; June, 55°; July, 61·6°;Aug. 56·6°; Sept. 46·6°; Oct. 38·6°; Nov. 24·6°. Julin andBuch. 6 Eastern coast of Western Bothnia. Dr. Nœzen. March,23·2°; April, 34°; Oct. 38·2°; Nov. 24·6°. 7 Euler. Mean temperature of the year, 38·2°. Inochodzow.Act. Petr. xii. 519—533. 8 Two years. Berlin, in the Mem. de l’Acad. de Drontheim,iv. 216. April, 34·4°; May, 50·8°; Oct. 39·2°; Nov. 27·8°.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.Chamounie, lat. 46° 1′; long. 3° 48′ E.; height, 3,168 feet;mean temperature, 39·2°. 10 Twelve years. Kirwan. Cotte, mean of the year, 41·2°;of the summer, 67·4°, too high. West coast of Finland. 11 Observations from 1774 to 1804, made by Mallet, Prosperin,Holmquist, and Schleling, calculated by M. De Buch. Voy. deNorw. ii. 309. It is, perhaps, the place the mean temperatureof which is the best determined. Winters more serene than atStockholm; colder on account of the radiation of the ground andthe air. 12 Thirty-nine years of observations, 15 of which are verygood. Wargentin. Cotte, mean temperature of the year, 44·2°.Five months below 32°, as at Petersburg. |191| 13 Four years. A transatlantic climate. 14 Buch, two years. Mean temperature of the winter scarcely29·5°. West coast. 15 Alps of Bavaria. Six years’ observations, calculated byM. Wahlenberg. Many fruit trees. Convent of Tegernsee, inBavaria, height of 2,292 feet; mean temperature of 1785; 42·2°;Peyssenberg, 41°. 16 Bugge. Three months below 32°. Under the equator,mean temperature of 44·6°, at an elevation of 18,000 feet. 17 Dalton. West of England. Climate of islands; springs47·2°. Keswick, lat. 54° 33′, long. 5° 23′ W.; mean tempera-ture, 48°; springs, 48·6°. 18 Kirwan. Scarcely two years’ observations. Southernlatitude. 19 Strnadt. Fifteen years. Climate of the continent ofEurope. 20 Mayer. 21 Six years’ observations of M. Escher, calculated by Wah-lenberg. The town is situated in a hollow, to which the 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 75·8°. Vegetation continuesfrom March 20 to Oct. 20; mean temperature of these sevenmonths is from 55·8° to 50·9°, according as the years are moreor less fruitful; wheat does not ripen if the mean temperaturedescends to 47·6°. 23 Guittard. Only three years. Mean temperature 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 of theclimate of the islands. Coldest days, 23°; interior of theground, 49·2°. Hamilton. 26 The climate of Berne is a continental climate, in comparisonwith that of Geneva; there is no lake near it. 27 Seven years of observations. Saussure. Mean temperature,50·8°. Voy. § 1418. I find the mean temperature from 1796—1815, 50°. Interior of the earth, 52°. Pictet, BibliothequeBrit. 1817. iv. 109. 28 Six years. 29 Austria. Berlin, lat. 52° 31′; mean temperature, probably46·4° to 47·3°; according to Beguelin, 48·8°; springs, 49·2°.Ratisbon, lat. 49°; height, 1,104 feet; mean temperature, 51·2°.Munich, lat. 48° 8′; height, 1,608 feet; mean temperature,50·8°. 30 Ramond. Seven years of excellent observations. Themean of the months, at noon, well ascertained; winter, 40°; |192|spring, 57°; summer, 70·8°; autumn, 58°. Mem. Inst. 1812.p. 49. Cotte, mean temperature, 51·2°. 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 temperature a little higher. Vaults, 53°. Kirwan findsfor Paris, from seven years of observations of unequal value,51·6°; he fixes upon 52·7°. Cotte, from 29 years of observa-tions (Journ. de Phys. 1782, July), 53·2°. Cotte, for 33 years,(1763—1781, Mem. Instit. iv. 266), 52·4°. The extraordinaryyear of 1816 offers the mean temperature of 48·8°; winter, 37·2°;spring, 49°; summer, 59·6°; autumn, 50°: the preceding year,1815, offers a mean temperature of 50·8°; winter, 37·2°; spring,52·7°; summer, 62·8°; autumn, 50·8°. Arago. Mean temper-ature of Montmorency, for 33 years, 50·8°; height, 498 feet.Cotte. Strasburg, lat. 48° 34′; height, 480 feet; mean tempera-ture, 49·2°. Herrenschneider. 34 Dr. Young. Mean temperature varies from 47·8° to 51·4°,(Lectures, ii. 453). Cavendish (Trans. 1788, p. 61), 48·8°,Roebuck, Hunter, and Kirwan, 51·6°. Horsley, 51·8°. Accord-ing to Kirwan, the four seasons in London are, 39·6°, 50·9°,64·8°, 52°; at Paris, 36·2°, 51°, 66°, 52·6°; from which results,London, 51·2°; Paris, 52·4°. Cotte (Journ. de Phys. xxxix.36) thinks London is 51·2°, and Paris, 52·4°. The differencewhich we observe in cultivated plants depends less upon meantemperature than upon direct light, and the serenity of the atmo-sphere. 35 Seven years. Cotte. Lisle, 48·4°; Rouen, 51·4°; Cam-bray, 52°; Soissons, 53·4°; Rethel, 53·2°; Metz, 53°; Nancy,52°; Etampes, 51°; L’Aigle, 49·8°; Brest, 54·2°; Mayenne,52°. 36 Mohr, and Van Swinden. Five years. 37 Thirteen years. Temperature rather too high? 38 Eleven years. Van Swinden. From 1771—1783. Meantemperature, 51·2°. 39 Concave transatlantic summit. Seven years of observa-tions give 54·8°; for the four seasons, 34°, 52°, 75·2°, 56·2°.Rush, 52·6 (Drake’s View of Cincin. p. 116). Coxe, 54·2°.M. Legaux finds for 17 years, for Springmill on the Schuylkill,lat. 40° 50′; mean temperature, 53·4. Springs, near Philadelphia,54·8°. Warden. 40 Two years only. Retif de la Serve. The thermometersometimes descends to —4° in the parallel of Naples! Springs,54·8°. Ipswich, lat. 42° 38′; mean temperature, 50°. Williams-burg, in Virginia, 58·1°. Cotte and Kirwan. Transatlanticclimates. |193| 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 low as—16·6°, for 39° latitude. Maximum, 89·6° to 107·6° in theshade, without reflection; \( \frac{1}{3} \) of all the winds S.W.; springsnear Cincinnati, 54·4°. Little snow falls; but it is abundantbetween lat. 40° and 42°. 42 Three years only. Bougourd. Dijon, height, 810 feet;lat. 47° 19′; mean temperature, 50·9°. Besançon, height, 804feet; lat. 47° 14′; mean temperature, 51° 2′. 43 Six years. Duplessis, and Boudan. Temperature of thesummer too high? Rochelle, 53°. Poitiers, 52·6°. 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 Astro-nomer Reggio, April, 55·8°; Oct. 58·1°. The two decadswhich approach the nearest to the mean temperature of the year,are, the first of April, 53·4°; and the last of Oct. 54·6°. Themean temperatures for January have varied in the last 10 yearsfrom 25° to 38·4°; those of July, from 71·4° to 78·4°; the meanof the years, from 54·5° to 57·2°. Reggio, taking only 24 maximaand minima in a year for 1763—1798; mean temperature,55·4° (Ephem. Mil. 1779, p. 82). 46 Ten years. Guyot. Lyon, 528 feet, 55·8°. Mafra, nearLisbon, lat. 38° 52′; height, 600 feet; mean temperature, 54·3°,too small. Mem. de Lisbonne, ii. 105—158. 47 Seven years (1777—1782). St. Jaques de Sylvabella. Thethermometer descends sometimes to 23°. Cotte (Traité de Met.ii. 420). 34 years (Raymond in Mem. de la Soc. de Med.1777, p. 86) give 62°. Cotte (Journ. de Phys. xxxix. 21)fixes it at 58·6°. Kirwan, at 61·4°. The observations made atthe Royal Observatory of Marseilles can alone decide. 48 Ten years. Nismes, 60·2°; Perpignan, 59·6; Tarascon,60°; Arles, 59°; Rieux, 57·2°; Montauban, 55·6°; Tonains,54·8°; Dax, 54·2°; Rodez, 57°; Aix, 56·6°. Under the equator,57·8°, at 9,000 feet of elevation. 49 William Humboldt. Calandrelli, 60°. The thermometersometimes descends to 36·5°, and rises to 99·5°. Naples, 67·1°;Toaldo, probably 63·5°; Florence, 61·6°; Tartini, too high;Lucca, 60·4°; Genoa, 60·2°; Bologna, 56·3°; Verona, 55·8°;Venice, 56·5°; Padua, 55·6°. Kirwan regards it as an esta-blished fact, that in Europe, the mean temperature, in latitude40°, is 61·8°; in latitude 50°, 52·6°. 50 Only two years. Barberet, and d’Angos. Sheltered bymountains. Estimate a little too high. 51 Japan. A single year. Voy. de Thunberg, p. 121.Climate of islands. Under the equator, 64·4°, at a height of6,000 feet. |194| 52 West of the Alleghanys, in Louisiana. Four years. Dunbar.Transatlantic climate. 53 Madeira. Heberden. Climate of islands. St. Croix, ofTeneriffe, 71·4°. The remainder of the island of Teneriffe, inthe plains, 61·2°. Buch. 54 Old observations of Tartebout. They appear good. Bag-dat, lat. 33° 19′; according to Beauchamps, 73·8°. The fourseasons, 50·8°, 74·6°, 92·6°, 77°; but there was reflectionfrom a house. The thermometer falls to 29·8°. Under theequator, at 3,000 feet high; mean temperature, 71·2°. 55 The calculations are made from the observations of Nouet(Decade, ii. 213). The following are the mean temperatures ofthe 12 months: 58·1°, 56·2°, 64·6°, 77·9°, 78·4°, 83·6°, 85·1°,85·8°, 79·2°, 72·2°, 63°, 68·6°. (Neibuhr, 72·2.) Temperatureof Joseph’s Well, 72·5°. Catacombs of Thebes, 81·4°. Well ofthe great pyramid surrounded by sand, 88·2°. Jomard. Bas-sora, on the Persian Gulf; mean temperature, 77·9°; winter,64°; summer, 90·8°; July, 93·2°. 56 Orta. Humboldt. Nouv. Esp. iv. 516. Jamaica, coast80·6°. Blagden. 57 Ferrer, 1810—1812. Con. des Tems. 1817, p. 338. Wellsof 10 feet deep; air, 76°; water, 74·4°; in 1812, maximum,Aug. 14, 86°; minimum, Feb. 20, 61·6°. Grottos, 81·5°. Hum-boldt, Observ. Astron. i. 134. 58 Humboldt. Pondicherry, 85·1°; Madras, 80·4°; Manilla,78·2°; Isle de France, coast, 80·4°.