On Isothermal Lines, and the Distribution of Heat over the Globe.

By Baron Alexander de Humboldt .

As this interesting and valuable Memoir, the original of which was published in the Memoires D’Arcueil, tom. iii. p. 462, has never appeared in our language, and as it must be constantly referred to in all subsequent speculations on Meteorology, and should be familiar to every person who pursues this important study, we have resolved to present a translation of it to our readers.

A small part of the memoir appeared in an English journal; but almost all the reductions from the Centigrade to Fahrenheit’s scale were so erroneous, that the numbers cannot be trusted.

We have added various notes, which will be distinguished from those of the Author by affixing Ed. to the former, and H to the latter.—Ed.

The distribution of heat over the Globe belongs to that kind of phenomena, of which the general circumstances have been long known, but which were incapable of being rigorously determined or submitted to exact calculation, till experience and observation furnished data from which the theory might obtain the corrections and the different elements which it requires.

The object of this memoir is to facilitate the collection of these data, to present results drawn from a great number of unpublished observations, and to group them according to a method which has not yet been tried, though its utility has been recognised for more than a century in the exposition of the phenomena of the variation and dip of the magnetic needle.

As the discussion of individual observations will be published in a separate work, I shall at present limit myself to a simple sketch of the distribution of heat over the globe, according to the most recent and accurate data.

Although we may not be able to refer the complex phenomena to a general theory, it will be of considerable importance to fix the numerical relation by which a great number of scattered observations are connected, and to reduce to empirical laws the effects of local and disturbing causes.

The study of these laws will point out to travellers the problems to which they should direct their principal attention, and we may entertain the hope, that the theory of the distribution of heat will gain in extent and precision, in proportion as observations shall be more multiplied, and directed to those points which it is of most importance to illustrate.

As the phenomena of geography and of vegetables, and in general the distribution of organised beings, depend on the knowledge of the three co-ordinates of Latitude, Longitude, and Altitude, I have been occupied for many years in the exact valuation of atmospherical temperatures; but I could not reduce my own observations without a constant reference to the works of Cotte and Kirwan, the only ones which contain a great mass of meteorological observations obtained by instruments and methods of very unequal precision.

Having inhabited for a long time the most elevated plains of the New Continent, I availed myself of the advantages which they present for examining the temperature of the superincumbent strata of air, not from insulated data, the results of a few excursions to the crater of a volcano, but from the collection of a great number of observations made day after day and month after month in inhabited districts.

In Europe, and in all the Old World, the highest points of which the mean temperatures have been determined, are the Convent of Peissenberg in Bavaria, and the Hospice of St Gothard . The first of these is placed at 3264, and the second at 6808 feet above the level of the sea.

In America a great number of good observations have been made at Santa Fe de Bogota and at Quito, at altitudes of 8,727 and 9,544 feet.

The town of Huancavelica, containing 10,000 inhabitants, and possessing all the resources of modern civilisation, is situated in the Cordilleras of the southern hemisphere at 12,310 feet of absolute elevation; and the mine of Santa Barbara, encircled with fine edifices, and placed a league to the south of Huancavelica, is a place fit for making regular observations, at the height of 14,509 feet, which is double that of the Hospice of St Gothard.

The mean temperature of the air at the Convent of the Great St Bernard, the height of which is 7,960 feet, is not determined.

There are several villages in Europe placed at more than 5000 feet of altitude; for example, St Jacques de Ayas at 5,479, and Trinita Nuova, near Grasfoncy, at 5,315 feet.—H.

These examples are sufficient to prove how much our knowledge of the higher regions of the atmosphere, and of the physical condition of the world in general, will increase, when the cultivation of the sciences, so long confined to the temperate zone, shall extend beyond the tropics into those vast regions, where the Spanish Americans have already devoted themselves with such zeal to the study of physics and astronomy.

In order to compare with the mean heat of temperate climates, the results which M.

Bonpland and I obtained in the equinoctial regions from the plains to the height of 19,292 feet, it was necessary to collect a great number of good observations made beyond the parallels of 30° and 35°. I soon perceived how vague such a comparison was, if I selected places under the meridian of the Cordilleras, or with a more eastern longitude, and I therefore undertook to examine the results contained in the most recent works.

I endeavoured to find, at every 10° of latitude, but under different meridians, a small number of places whose mean temperature had been precisely ascertained, and through these, as so many fixed points, passed my isothermal lines or lines of equal heat.

I had recourse, in so far as the materials have been made public, to those observations the results of which have been published, and I found, in the course of this easy, but long and monotonous labour, that there are many mean temperatures pointed out in meteorological tables, which, like astronomical positions, have been adopted without examination.

Sometimes the results were in direct contradiction to the most recent observations, and sometimes it was impossible to discover from whence they were taken.

Many good observations were rejected, solely because the absolute height of the place where they were made was unknown.

This is the case with Asia Minor, Armenia and Persia, and of almost all Asia; and while the equinoctial part alone of the New World presents already more than 500 points, the greater number of which are simple villages and hamlets, determined by barometrical levelling, we are 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 stood with Persia and Candahar, this branch of knowledge has not made any progress in the last fifty years.

We are not authorised, however, on account of the decrease of temperature in the upper regions of the atmosphere, to confound the mean temperatures of places which are not placed on the same level.

In the Old World, good observations, which can alone be used for establishing empirical laws, are confined to an extent between the parallels of 30 and 70 degrees of latitude, and the meridians of 30° east longitude, and 20° of west longitude.

The extreme points of this region are the island of Madeira, Cairo, and the North Cape. It is a zone which is only a thousand nautical leagues, (1|7th of the circumference of the globe,) from east to west, and which, containing the Basin of the Mediterranean, is the centre of the primitive civilisation of Europe.

The extraordinary shape of this part of the world, the interior seas and other circumstances, so necessary for developing the germ of cultivation among nations, have given to Europe a particular climate, very different from that of other regions placed under the same latitude. But as the physical sciences almost always bear the impress of the places where they began to be cultivated, we are accustomed to consider the distribution of heat observed in such a region, as the type of the laws which govern the whole globe.

It is thus that, in geology, we have for a long time attempted to refer all volcanic phenomena to those of the volcanoes in Italy.

In place of estimating methodically the distribution of heat, such as it exists on the surface of continents and seas, it has been usual to consider as real exceptions every thing which differs from the adopted type, or, by pursuing a method still more dangerous in investigating the laws of nature, to take the mean temperatures for every five degrees of latitude, confounding together places under different meridians.

As this last method appears to exclude the influence of extraneous causes, I shall first discuss it briefly before I proceed to point out the method, essentially different, which I have followed in my researches.

The temperature of the atmosphere, and the magnetism of the globe, cannot, like those phenomena which depend on one cause, or on a single centre of action, be disengaged from the influence of disturbing circumstances, by taking the averages of many observations in which these extraneous effects are mutually destroyed.

The distribution of heat, as well as the dip and variation of the needle, and the intensity of the terrestrial magnetism, depend, by their nature, on local causes, on the constitution of the soil, and on the particular disposition of the radiating surface of the globe.

We must, however, guard against confounding under the name of extraneous and disturbing causes, those on which the most important phenomena, such as the distribution and the more or less rapid developement of organic life, essentially depend.

Of what use would it be to have a table of magnetic dips, which, in place of being measured in parallels to the magnetic equator, should be the mean of observations made on the same degrees of terrestrial latitude, but under different meridians?

Our object is to ascertain the quantity of heat which every point of the globe annually receives, and, what is of most importance to agriculture, and the good of its inhabitants, the distribution of this quantity of heat over the different parts of the year, and not that which is due to the solar action alone, to its altitude above the horizon, or to the duration of its influence, as measured by the semidiurnal arcs.

Moreover, we shall prove, that the method of means is unfit for ascertaining what belongs exclusively to the sun, (inasmuch as its rays illuminate only one point of the globe,) and what is due both to the sun and to the influence of foreign causes.

Among these causes may be enumerated the mixture of the temperatures of different latitudes produced by winds;—the vicinity of seas, which are immense reservoirs of an almost invariable temperature;—the shape, the chemical nature, the colour, the radiating power and evaporation of the soil;—the direction of the chains of mountains, which act either in favouring the play of descending currents, or in affording shelter against particular winds;—the form of lands, their mass and their prolongation towards the poles;—the quantity of snow which covers them in winter, their temperature and their reflection in summer;— and, finally, the fields of ice, which form, as it were, circumpolar continents, variable in their extent, and whose detached parts dragged away by currents modify in a sensible manner the climate of the temperate zone.

In distinguishing, as has long been done, between the solar and the real climate, we must not forget, that the local and multiplied causes which modify the action of the sun upon a single point of the globe, are themselves but secondary causes, the effects of the motion which the sun produces in the atmosphere, and which are propagated to great distances.

If we consider separately (and it will be useful to do this in a discussion purely theoretical) the heat produced by the sun, the earth being supposed at rest and without an atmosphere, and the heat due to other causes regarded as disturbing ones, we shall find that this latter part of the total effect is not entirely foreign to the sun.

The influence of small causes will scarcely disappear by taking the mean result of a great number of observations; for this influence is not limited to a single region.

By the mobility of the aerial ocean, it is propagated from one continent to another.

Every where in the regions near the polar circles, the rigours of the winters are diminished by the admixture of the columns of warm air, which, rising above the torrid zone, are carried towards the poles: Every where in the temperate zone, the frequent west winds modify the climate, by transporting the temperature of one latitude to another . When we reflect, besides, 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 meridians of Canton and of California, we shall perceive, that even if the number of observations on the mean temperature were infinite, the compensation would not take place.

Raymond, Memoire sur la Formule Baromet. p. 108 and 113.

It is, then, from the theory alone that we must expect to determine the distribution of heat over the globe, in so far as it depends on the immediate and instantaneous action of the sun.

It does not indicate the degrees of temperature expressed by the dilatation of the mercury in a thermometer, but the ratios between the mean annual heat at the equator, at the parallel of 45°, and under the polar circle; and it determines the ratios between the solstitial and equinoctial heats in different zones. By comparing the results of calculation, not with the mean temperature drawn from observations made under different longitudes, but with that of a single point of the earth’s surface, we shall set out with that which is due to the immediate action of the sun, and to the whole of the other influences, whether they are solar or local, or propagated to great distances.

This comparison of theory with experience 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, Halley laid the first foundations of a theory of the heating action of the sun under different latitudes .

He proved that these actions might compensate for the effect of the obliquity of the rays.

The ratios which he points out, do not express the mean heat of the seasons, but the heat of a summer day at the equator and under the polar circle, which he finds to be as 1.834 to 2.310 . According to Geminus , Polybius among the Greeks had perceived the cause why there should be less heat at the equator than under the tropic.

The idea also of a temperate zone, habitable and highly elevated in the midst of the torrid zone, was admitted by Eratosthenes , Polybius, and Strabo.

Phil. Trans. 1693, p. 878.

This should be 2.339.—Ed.

Isag. in Aratum, cap. 13.; Strabo, Geogr. lib. ii. p. 97.

In two memoirs , published at long intervals in 1719 and 1765, Mairan attempted to solve the problems of the solar action, by treating them in a much more extended and general manner.

He compared, for the first time, the results of theory with those of observation; and as he found the difference between the heat of summer and winter much less than it ought to be by calculation, he recognised the permanent heat of the globe and the effects of radiation.

Mem. de l’Acad. 1719, p. 133; and 1765, p. 145. and 210.

Without mistrusting the observations he employed, he conceived the strange theory of central emanations which increase the heat of the atmosphere from the equator to the pole.

He supposes that these emanations decrease to the parallel of 74°, where the solar summers attain their maximum, and that they then increase from 74° to the pole.

Lambert , with that sagacity which distinguishes all his mathematical researches, has pointed out in his Pyrometrie the error of Mairan’s theory.

He might have added, that this geometer confounds a quantity of heat which a point of the globe receives under the latitude of 60° during the three months of summer, with the maximum to which the inhabitants of these northern regions see their thermometers rising in a clear day.

The mean temperatures of the summers, far from decreasing from the pole to the tropics, are under the equator, under the parallel of 45°, and under that of Stockholm, Upsal, or St Petersburg, in the ratio of 81°.86; 69°.8; 61°.16 of Fahrenheit’s scale.

Reaumur had sent his new thermometers to the torrid zone, to Syria, and to the north.

As it was then reckoned sufficient to mark the warmest days, an idea was formed of an universal summer, which is the same in all parts of the globe.

It had been remarked, and with reason, that the extreme heats are more frequent, and even more powerful, in the temperate zone in high latitudes, than under the torrid zone.

Without attending to the mean temperature of months, it was vaguely supposed, that in these northern regions the summers followed the ratio of the thermometrical extremes.

This prejudice is still propagated in our own day, though it is well established, that in spite of the length of the days in the north, the mean temperatures of the warmest months at Petersburg, Paris, and the Equator, are 65°.66; 69°.44, and 82°.

4. At Cairo, according to the observations of Nouet, the three months of summer are 84°.74, and consequently 19° warmer than at St Petersburg, and 15° warmer than at Paris.

The summer heats of Cairo, are almost equal to those I have experienced at Cumana and La Guayra between the tropics.

Pyrometrie oder Vom Maase des Feuers, 1779, p. 342.

With regard to the central emanation of the system of Mairan, or to the quantity of heat which the earth gives to the ambient air, it is easy to conceive that it cannot act in all seasons.

The temperature of the globe at the depths to which we can reach, in general differs little from the mean annual temperature of the atmosphere.

Its action is of great importance for the preservation of vegetables; but it does not become sensible in the air, unless where the surface of the globe is not entirely covered with snow, and during those months, whose mean temperature is below that of the whole year.

In the south of France, for example, the radiation of the earth may act upon the atmosphere in the five months which precede the month of April.

We speak here of the proper heat of the globe, of that which is invariable at great depths, and not of the radiation of the surface of the globe, which takes place even at the summer solstice, and the nocturnal effects of which have furnished M. Prevost with an approximate measure of the direct action of the sun .

Du Calorique rayonnant, p. 271. 277. 292.

Mairan had found, that in the temperate zone the heat of the solar summer is to that of the solar winter as 16 to 1. M. Prevost admits for Geneva 7 to 1. Good observations have given me for the mean temperature of the summers and the winters at Geneva 34°.7; 64°.94; and at St Petersburg 46°.94 and 62°.06.

These numbers neither express ratios nor absolute quantities, but thermometrical differences considered as the total effect of the calorific influences; the ratios furnished by theory separate the solar heat from every other indirect effect.

Euler was not more successful than Mairan in his theoretical essays on the solar heat.

He supposes that the negative sines of the sun’s altitude during the night give the measure of the nocturnal cooling, and he obtains the extraordinary result , that under the equator the cold at midnight ought to be more rigorous than during winter, under the poles.

Fortunately, this great geometer attached but little importance to this result, and to the theory from which it is deduced.

The second memoir of Mairan, without adding to the problems which had been attempted since the time of Halley, has at least the advantage of containing some general views on the real distribution of heat in different continents.

It is true, that the extreme temperatures are there constantly confounded with the mean temperatures; but previous to the works of Cotte and Kirwan, it was the first attempt to group the facts, and to compare the most distant climates.

Comment. Petrop. tom. ii. p. 98.

Dissatisfied with the route followed by his predecessors, Lambert, in his Treatise on Pyrometry, directed his attention to two very different objects.

He investigated analytical expressions for the curves, which express the variation of temperature in a place where it had been observed, and he resumed in its greatest generality the theorem of solar action.

He gives formulæ, from which we may find the heat of any day at all latitudes; but being perplexed with the determination of the nocturnal dispersion of the acquired heat, or the subtangents of the nocturnal cooling , he gives tables of the distribution of heat under different parallels, and in different seasons , which deviate so much from observation, that it would be very difficult to ascribe these deviations to the heat radiating from the globe, and to disturbing causes.

We are struck with the slight difference which the theory indicates between the mean annual temperatures of places situated under the equator and the polar circle, and between the summers of the torrid zone and those of the temperate zone. It cannot be expected, indeed, that analysis is capable of determining the distribution of heat such as it exists on the surface of the globe.

Without employing empirical laws, and deducing the data from actual observation, the theory can subject to calculation only a part of the total effect, or that which belongs to the immediate action of the solar rays; but after the recent successful applications of analysis to the phenomena of the radiation of surfaces, the transmission of heat through solid bodies, and the cooling of these bodies in media of variable density, we may still expect to be able to perfect the theory of solar action, and to compute the distribution of the heat received into the exterior crust of our planet.

Pyrometrie, p. 141, 179.

Id. 318, 339.

In discussing what may be expected from the purely theoretical labours of Geometers, I have not spoken of a celebrated, but very concise Memoir of Mayer, the reformer of the Lunar Tables.

This work, written in 1755, was published twenty years afterwards, in his Opera Inedita .

It is a method, and not a theory:

It is an essay essentially different from those we have quoted, and, as its learned author calls it, a determination of the mean heat found empirically by the application of coefficients furnished by observation.

The method of Mayer is analogous to that which Astronomers pursue with so much success, when they correct by small steps the mean place of a planet, by means of the inequalities of its motion:

It does not present the result of the solar action disengaged from the influence of foreign circumstances; but, on the contrary, it estimates the temperatures such as they are distributed over the globe, whatever be the cause of that distribution.

The mean heat of two places situated under different latitudes being given, we find by a simple equation the temperature of every other parallel . The calculations of Mayer, according to which the temperatures decrease from the equator to the poles, as the squares of the sines of the latitudes, give results sufficiently precise, when the place does not differ much in longitude from that of the regions where the empirical co-efficients have been obtained.

But, even in the northern hemisphere, when we apply the formula to places situated 70° or 80° to the east or west of the meridian of Paris, the calculated results no longer agree with observation.

The curve which passes through those points whose temperature is 32°, does not coincide with any terrestrial parallel.

If, in the Scandinavian Peninsula, we meet with this curve under the 65th or 68th degree of latitude, it descends, on the contrary, in North America, and Eastern Asia, to the parallel of from 53° to 58°.

But the direction and the inflexions of this curve of 32° of temperature influences the neighbouring isothermal lines in the same manner as the inflexions of the magnetic equator modify the lines of inclination.

To demand what is the mean temperature, or what is the magnetic inclination under a particular degree of latitude, is to propose problems equally indeterminate.

Though, even in high latitudes the magnetic and the isothermal lines are not rigorously parallel to the magnetic equator, and to the curve of 32° of temperature; yet it is the distance of any place from this curve which determines the mean temperature, as the inclination of the needle depends on the magnetic latitude.

De Variationibus Thermometri accuratius definiendis, (Opera inedita, vol. i. p. 3—10.) M. Daubuisson, in a note inserted in the Journal de Physique, tom. lxii. p. 449. has given a formula which accords better with observation than that of Mayer.

He admits that the temperature increases from the pole to the equator, as the cosine of the latitude raised to the power of 2 [Formel] °; but he judiciously adds, that this formula is applicable only to a zone of the Old World, near the Northern Atlantic Ocean—H.

The formula given by Mayer was T = 24 cos 2 Lat.; or T = 12 + 12 cos 2 Lat. for Reaumur’s scale; and T = 84—52 sin 2 Lat., or T = 58 + 26 cos 2 Lat. for Fahrenheit’s scale.

Since the publication of Humboldt’s memoir, M. Daubuisson has resumed the subject of the earth’s temperature in his Traité de Geognosie, tom. i. p. 424. Paris, 1819.

He gives the following formula, which is almost the same as that of Mayer, for finding the mean temperature, according to the Centigrade scale, viz.

T = 27° cos 2 Latitude.

This formula, which is superior in accuracy to Mayer’s, gives all the temperatures in defect for latitudes below 42°, and in excess for all the higher latitudes, as appears from Daubuisson’s table.

It is therefore obviously defective. M.

Daubuisson, however, considers it as applicable principally between the parallels of 30° and 60° of N. lat.

It ought to be remarked, that in the above formula, 27° has been assumed as the mean temperature of the equator, in order to make the results agree with observations made in the temperate regions, whereas the mean temperature of the equator, as ascertained by Humboldt, is 27°.5; and if this were used in Daubuisson’s formula, it would make the differences still more in excess.— Ed.

These considerations are sufficient to prove, that the empirical formulæ of Mayer require the introduction of a co-efficient, which depends upon the longitude, and consequently on the direction of the isothermal lines and their nodes with the terrestrial parallels.

Mayer had no intention of disengaging the results which he obtained from the influence of all disturbing causes:

He limited himself to the determination of the effects of altitude above the level of the sea, and those of the seasons, and the length of the day.

He wished to point out the way which philosophers ought to pursue in imitating the method of astronomers.

His Memoir was written at a time when we did not know the mean temperature of three points on the globe; and the corrections which I propose after tracing the isothermal lines, so far from being incompatible with the method of Mayer, are, on the contrary, among the number of those which this geometer seems to have indistinctly foreseen.

Kirwan, in his work on Climates, and in a learned Meteorological Memoir, inserted in the eighth volume of the Memoirs of the Irish Academy, attempted at first to pursue the method proposed by Mayer, but, richer in observations than his predecessors, he soon perceived, that after long calculations, the results agreed ill with observation . In order to try a new method, he selected, in the vast extent of sea, those places whose temperature suffered no change but from permanent causes.

These were in the part of the great ocean commonly called the Pacific Ocean, from 40° of South to 45° of North latitude, and in the part of the Atlantic Ocean, between the parallels of 45° and 80°, from the coasts of England to the Gulf Stream, the high temperature of which was first determined by Sir Charles Blagden.

Kirwan tried to determine for every month the mean temperature of these seas at different degrees of latitude; and these results afforded him terms of comparison with the mean temperatures observed on the solid part of the terrestrial globe.

It is easy to conceive, that this method has no other object, but to distinguish in climates that is in the total effect of calorific influences, that which is due to the immediate action of the sun on a single point of the globe.

Kirwan first considers the earth as uniformly covered with a thick stratum of water, and he then compares the temperatures of this water at different latitudes, with observations, at the surface of continents indented with mountains, and unequally prolonged towards the poles.

Kirwan’s Estimate of the Temperature of the Globe, chap. iii.

This interesting investigation may enable us to appreciate the influence of local causes, and the effect which arises from the position of seas, on account of the unequal capacity of water and earth for absorbing heat.

It is even better fitted for this object than the Method of Means deduced from a great number of observations made under different meridians; but in the actual state of our physical knowledge, the method proposed by Kirwan cannot be followed.

A small number of observations made far from the coasts, in the course of a month, fixes, without doubt, the mean annual temperature of the sea at its surface, and, on account of the slowness with which a great mass of water follows the changes of the temperature of the surrounding air, the extent of variations in the course of a month is smaller in the ocean than in the atmosphere:

But it is still greatly to be desired , that we should be able to indicate by direct experience, for every parallel, and for every month, the mean temperature of the ocean under the temperate zone.

The scheme which Kirwan has formed for the extent of the seas, that ought to form the term of comparison, is founded only in a small degree upon the observations of navigators, and to a great degree on the theory of Mayer.

He has also confounded experiments made on the superficial temperature of the ocean with the results of meteorological journals, or the indications of the temperature of the air which rests upon the sea:

He has obviously reasoned in a circle, when he modified, either by theoretical suppositions or by observations made on the air upon the coasts of continents, the table of the temperature of the ocean, in order to compare afterwards with these same results, partly hypothetical, those which observation alone furnished in the interior of the earth.

After the works of Kirwan, we must notice those of Cotte, which are merely laborious, though useful, compilations, which, however, ought not to be used without much circumspection.

A critical spirit has rarely presided over the reduction of the observations, and they are not arranged so as to lead to general results.

See my Relation Historique, tom. i.

In detailing the actual state of our knowledge on the distribution of heat, I have shewn how dangerous it is to confound the results of observation with theoretical deductions.

The heat of any point of the globe depends on the obliquity of the sun’s rays, and the continuance of their action, on the height of the place, on the internal heat and radiation of the earth in the middle of a medium of variable temperature; and, in short, upon all those causes which are themselves the effects of the rotation of the earth, and the inequal arrangement of continents and seas.

Before laying the foundation of a system, we must group the facts, fix the numerical ratios, and, as I have already pointed out, submit the phenomena of heat, as Halley did those of terrestrial magnetism, to empirical laws.

In following this method, I have first considered whether the method employed by meteorologists for deducing the mean temperature of the year, the month and the day, is subject to sensible errors.

Assured of the accuracy of the numerical averages, I have traced upon a map the isothermal lines, analogous to the magnetic lines of dip and variation.

I have considered them at the surface of the earth in a horizontal plane, and on the declivity of mountains in a vertical plane.

I have examined the increase of temperature from the pole to the equator, which is inequal under different meridians; the distribution of the same quantity of heat over the different seasons, in the same isothermal parallel, and under different latitudes; the curve of perpetual snows, which is not a line of equal heat; the temperature of the interior of the earth, which is a little greater towards the north, and in high mountains, than the mean temperature of the atmosphere under the same parallel; and, lastly, the distribution of heat in the ocean, and the position of those bands, which may be called Bands of the warmest waters.

As the limits of this extract will not permit me to enter, in a detailed manner, upon these different discussions, I shall confine myself solely to the principal results.

It was formerly the custom to take the maximum and minimum of temperature observed in the course of a year, and to consider half the sum as the mean temperature of the whole year.

This was done by Maraldi, De la Hire, Muschenbröek, Celsius, and even Mairan, when they wished to compare the very warm year of 1718 with the excessively cold years of 1709 and 1740.

De la Hire was struck with the identity between the uniform temperature of the caves of the Observatory of Paris, and the mean of the observed annual extremes.

He appears to have been the first who had an idea of the mean quantity of heat which a point of the globe receives; and he adds, “We may regard the air of the caves as the mean state of the climate .” Reaumur followed also the method of a maximum, though he confessed that it was incorrect .

He noticed the hours at which it was necessary to make observations; and after 1735, he published in the Memoirs of the Academy the extremes of daily temperature: he even compared the produce of two harvests with the sum of the degrees of heat to which during two consecutive years the crops had been exposed.

When he treated, however, of the mean temperature of the month, he contented himself, as Duhamel did thirty years afterwards, with recording three or four thermometrical extremes.

In order to have some idea of the errors of this imperfect method, I may state, that even in 1777, the mean temperature of Toulon was estimated by Cotte at 78°.08, though he afterwards found, by employing the whole mass of observations, that it was not more than 60°.26.

Mem. de l’Acad. 1719, p. 4.

Id. 1735, p. 559.

Mem. de la Soc. Royale de Med. 1777, p. 104.

In order to diminish the errors of the method of annual extremes, it was perceived, though very late, that it was necessary to subdivide the curve which expresses the variation of temperature.

Twenty-four extremes divided among twelve months of the year, give an annual mean more exact than the two extremes of all the observations.

The ordinates do not increase uniformly and uninterruptedly up to the maximum of the year, and there are partial inflexions sufficiently regular.

The more we subdivide, and the more we know the terms in the series, the more will these terms approximate, and the less error will there be in the supposition of an arithmetical progression, and in that of the equidistance of the different maxima and minima of temperature.

These considerations enable us to appreciate the three methods according to which observations are at present made.

1. Observations are made three times a-day, at sunrise and sunset, and at two o’clock in the afternoon.

This was done at Geneva during the three years 1796, 1797 and 1798.

In the observations, the hour of mid-day was preferred to that of sunset.

2. Observations are made twice every day, at the two periods which are supposed to give the maximum and the minimum, namely, at sunrise, and at two o’clock in the afternoon.

3. Observations are made once a-day, at an hour which, in different seasons, has been found to represent the mean temperature of the day.

It is thus that M. Raymond, by a judicious induction, has proved, that the height of the barometer, at mid-day, gives, in our climates, the mean atmospherical pressure, corrected for the diurnal variation.

In calculating a great number of observations made between the parallels of 46° and 48°, I have found, that a single observation at sunset, gives a mean temperature which differs only some tenths of a degree from that which is deduced from observations made at sunrise and at two o’clock.

The deviations of different months, do not exceed 1°.8, and they are very regularly positive or negative, according to the order of the seasons. M.

Arago has examined for seven years the observations of noon.

They give for Paris 5°.4 more than the mean temperature of the whole year.

Upon high mountains in the temperate zone, the difference is scarcely 1°8 .

By the application of coefficients, variable according to the latitude and the elevation, we may deduce the true mean temperatures from observations made at any particular period of the day, nearly in the same manner as we can ascertain the latitude of a place from altitudes of the sun, taken out of the meridian.

De la Formule Barom. p. 213.

The mean of the observations at noon at Paris was 56°.84; at Clermont in Auvergne (elevation 1348 feet), 56°,30; at Strasburg (elevation 453 feet), 55°.22.

Bulletin de la Soc. Philom.

1814, Oct. p. 95.—H.

At the Hospice of St Gothard.

Ephem. Soc. Pal. 1785, p. 47.

If we do not stop at two observations of the maximum and minimum, but add a third observation, we commit an error more or less serious, if we divide simply by three the sum of the observations, without attending to the duration of the partial temperatures, and to the place which the third observation occupies between the last terms of the series . Experience proves, that the mean temperatures of the year, obtained by two or three observations, do not differ sensibly, if the 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 intermediate temperatures, we should prefer the two observations of the extreme temperature, which is the method most generally adopted.

We shall content ourselves with pointing out the errors to which it is liable.

In our 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 ought to take into account the duration of the partial temperature, in order to find the quantity of heat divided between the night and the day, we must couple the maximum of one day with the minimum of the day following, and not be content with taking half the sum of all the maxima and minima of a month.

In the ordinary method, we determine only the mean temperature of the part of the day comprehended between the rising of the sun and two o’clock in the afternoon; and we take it for granted that the mean temperature is the same from two o’clock to sunrise next day.

This double error, of want of equi-distance and of the coupling of observations, does not in general produce errors of more than some tenths of degrees, sometimes in excess, and sometimes in defect, since the warm and cold days are mixed .

Example.—On the 13th June, at 4h in the morning, 46°.4; at 2h in the afternoon, 55°.4; and at 11h in the evening, 50°, (erroneously 46°.4, or 8° Centig. in the original).

In calculating by the duration, we have The true mean of which is 51°.

0. The mean of the three observations, as commonly taken, is 50°.6.

If we stop at the two extreme temperatures, we shall have for their half sum 50°.45.—H.

50°.9 the mean for 10h of interval, = 509°.0 52.7 9 = 474.3 48.2 5 = 241.0

Example.—At sunrise at 6h, 50°; at 2 o’clock in the afternoon, 62°.

6. At sunset, 51°.8; at 2h, 66°.2; at sunrise, 50°.

The true means will be for the first 24 hours 56°.9, and for the second 59°.0, for we shall have The method commonly employed gives [Formel] (50° + 62°.6) = 56°.3, and [Formel] (66°.2 + 51°8) = 58°.

1. The errors being — 0°.6 and + 0,9, sometimes positive and sometimes negative.—H.

For 8h, [Formel] (50°.0 + 66°.2) × 8 = 450°.4 for 8h = 472°.0

16 [Formel] (51°.8 + 62°.6) × 16 = 915°.2 for 16h = 929°.6

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.—H.

All the calculated results will err in defect, if the 365 ordinates, through which the curve of the year passes, do not express an arithmetical progression, and if the partial irregularities do not sensibly compensate one another.

It is only on this supposition that we can judge by the extreme terms of the series, of the sum of the terms, that is, of the partial temperatures.

It is very obvious, that near the maximum, the increase ought to be more slow than in other points of the curve, and that this increase in the temperature of the air ought to depend on the sine of the sun’s altitude, and on the emission of the radiant heat of the globe.

It appeared to me very important to establish, by observations made at every hour, at different periods of the year, and under different latitudes, the degree of confidence that can be placed in those results which are called Mean Temperatures. I have selected from the registers of the Royal Observatory at Paris clear and calm days, which offered at least ten or twelve observations.

Under the equator, I have spent whole days in determining the horary increments and decrements of temperature, in marking the thermometer both in the shade and in the sun, and also the progress of evaporation and humidity; and in order to avoid calculation, I measured with a quadrant the altitude of the sun at each observation.

I chose days and nights completely calm, and when the heavens were entirely free from clouds, because the mass of vesicular vapours interrupts the radiation from the earth.

The result of these experiments has been very satisfactory, and proves, what had already been deduced from the coincidence between the temperature of the earth and the mean of daily observations, and from the regular progress of the mean temperatures of months in different years, that the effects of small disturbing causes may be compensated by a great number of observations . I have obtained analogous results by taking, for several months, the mean of 9 o’clock in the morning, of sunrise and midnight.

I have computed the temperatures by the distance of the maximum expressed in time, and on the supposition of an arithmetical progression.

I have found that, under the Torrid Zone, the morning curve from sunrise to the maximum, differs very regularly from the evening curve.

In the morning the true mean temperature, such as we find by taking the duration into account, is a little greater than half the sum of the extremes . In the evening the error is in a contrary direction, and the series of temperatures approaches more to a progression by quotients.

The differences do not in general exceed half a degree, and calculation proves that the compensation is regular.

It would be curious to examine the effect which the radiation of the earth has on these horary effects, as the changes of temperature at the surface do not follow the geometrical progression, in so far as they take place in a medium of uniform temperature.

On the 3d and 4th September 1811, lat. 48°.50′.

The three last days shew an equality of temperature, which is very surprising, and which does not appear but in the true means.—H.

Sum of the temperatures during 24 hours.

True mean temperature, taking into account the duration.

Half sum of the two extreme temperatures.

625°.71 Fahr.

57°.92 Fahr.

58°.28 Fahr. 672.49 59.90 61.88 834.67 66.74 65.12 834.67 66.74 68.00 835.37 66.74 63.50 ——— ——— 63.61 Mean. 63.35 Mean.

Example.—Latitude 10°.25′. H.

Calculation of a true mean by the duration.

Supposition of an arithmetical progression.

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

In order to avoid the use of an arbitrary measure, astronomers express 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 the equatorial heat, but by the arithmetical ratios which subsist between this heat and that of the other parallels.

This method frees us from the want of uniformity, which arises from the use of different thermometers.

Instead of saying that in Europe, under the parallel of 45°, the mean temperature is 13°.4 Centigrade, or 56°.12 of Fahrenheit, we say that it is = 1.0°,487, and in lat. 55° = 1.0°,29.

These arithmetical ratios inform us of what is most interesting in the theory of the distribution of heat, that in thermometers whose zero is the point of melting ice, the mean temperatures under the latitude of 45° and 55° are, in our regions, the half and the third nearly of the equatorial temperature, which I suppose to be 81°.5.

(To be continued.)

— On Isothermal Lines, and the Distribution of Heat over the Globe.

By Baron Alexander de Humboldt.

(Continued from Vol. III. p. 20.)

Having discussed the method of taking averages, and of reducing temperatures to general expressions, we shall now proceed to trace the course of the Isothermal Lines on the surface of the Globe, and at the level of the sea.

From a slight attention to the difference of climates, it has been remarked, more than a century ago, that the temperatures are not the same under the same parallels; and that in advancing 70° to the east or the west, the heat of the atmosphere suffers a sensible diminution.

In pursuance of our method, we shall reduce these phenomena to numerical results, and shew that places situated under the same latitudes do not differ, in America and Europe, by the same number of degrees of temperature, as has been vaguely stated.

This assertion would make us suppose that the isothermal lines are parallel in the temperate zone.

Lat. Mean Temp. I. Parallels of Georgia, of the State of Mississippi, of Lower Egypt, and Madeira.

Natches, ‒ 31°28′ 64° 8′ Funchal, ‒ 32 37 68 7 Orotava, ‒ 28 25 69 8 Rome, ‒ 41 53 60 4 Algiers, ‒ 36 48 70 0 ——— ——— Difference, 7 0 4 1 Lat. Mean Temp. II.

Parallels of Virginia, Kentucky, Spain, and the South of Greece.

Williamsburg, 38° 8′ 58° 0′ Bourdeaux, 44 50 56 5 Montpellier, 43 36 59 4 Rome, ‒ 41 53 60 4 Algiers, ‒ 36 48 70 0 ——— ——— Difference, 7 0 7 7 III.

Parallels of Pennsylvania, Jersey, Connecticut, Latium, and 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 62 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 of Sweden, and Courland.

Nains, ‒ 57 0 26 4 Okak, ‒ 57 20 29 8 Umea, ‒ 63 50 33 3 Enontekies, 68 30 27 0 Edinburgh, 55 58 47 8 Stockholm, 59 20 42 3 ——— ——— Difference, 11 0 17 1

The differences under the column of latitudes, is the difference of the latitude of a place in Europe and a place in America, which have the same mean temperature; and the differences under the column of mean temperatures, is the difference of the mean temperatures of a place in Europe and a place in America, which have the same latitude.—Ed.

This table indicates the difference of climates, expressed by that of the mean temperature, and by the number of degrees in latitude which it is necessary to go northward in Europe, in order to find the same quantity of annual heat as in America .

As a place could not be found in the Old World, whose mean temperature was 48° the same as that of Williamsburg, I have supplied it with an interpolation between the latitudes of two points whose mean temperatures are 56°.5 and 59°.

4. By an analogous method, and by employing only good observations, I have found that

See my Prolegomena de distributione geographica plantarum, secundum cœli temperiem et altitudinem montium. p. 68.—H.

1. The isothermal line of 32° (0° centig.) passes between Uleo and Enontekies in Lapland (lat. 66° to 68°; East long. from London 19° to 22°), and Table Bay in Labrador (lat. 54° 0′, west long. 58°.)

2. The isothermal line of 41° (5° centig.) passes by near Stockholm (lat. 60° east long. 18°) and the Bay of St George in Newfoundland (lat. 48°, and long. 59°.)

3. The isothermal line of 50° (10° centig.) passes by Belgium (lat. 51°, east long. 2°) and near Boston (lat. 42° 30′, west long. 70° 59.)

4. The isothermal line of 59° (15° centig.) passes between Rome and Florence (lat. 43° 0′, east long. 11° 40′) and near Raleigh in North Carolina (lat. 36° 0′, and west long. 76° 30′.)

The direction of these lines of equal heat, gives for the two systems of temperature, which we know by precise observations, viz. part of the middle and west of Europe, and that of the coast of America, the following differences:

Latitude.

Mean Temp.

of the west of the Old World.

Mean Temp.

of the east of 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 half of this temperature in the Old World at 45°, and in the east of the New World, at 39° of lat .

This observation relates to the Centigrade scale.

If we count the temperatures from 32°, it applies also to Fahrenheit’s scale.—Ed.

The mean temperatures decrease

Latitude. Temp. Temp. From 0°—20° In the Old World, 3°.6 In the New World, 3°.6 20 — 30 7.2 10.8 30 — 40 7.2 12.6 40 — 50 12.6 16.2 50 — 60 9.9 13.3 0 — 60 40.5 56.5

In both continents, the zone in which the mean temperature decreases most rapidly is comprehended between the parallels of 40° and 45°.

Observation here presents a result entirely conformable to theory, for the variation of the square of the cosine, which expresses the law of the temperature, is a maximum towards 45° of latitude.

This circumstance ought to have a favourable influence on the civilization and industry of the people who inhabit the regions under this mean parallel.

It is the point where the regions of the vines touch those of the olives and the citrons.

On no other part of the globe, in advancing from north to south, do we observe the temperatures increase more sensibly, and no where else do vegetable productions, and the various objects of agriculture, succeed one another with more rapidity.

But a great difference in the productions of contiguous countries, gives activity to commerce, and augments the industry of the cultivators of the soil.

We have traced the direction of the isothermal lines from Europe to the Atlantic Provinces of the New World.

We have seen them approach one another from parallelism towards the south, and converge towards the north, particularly between the thermometric curves of 41° 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 the meridian, and nearly parallel to the coasts which are opposite to Europe and Asia, viz. the chain of the Alleghanys and the Rocky Mountains, which divide the waters of the Missouri and the Columbia.

Between these chains stretch the vast basin of the Mississippi, the plains of Lousiana, and of the Tenessee, and the states of Ohio, the centre of a new civilization.

It is generally believed in America that the climate is more mild to the west of the Alleghany Mountains, than under the same parallels in the Atlantic States .

Mr Jefferson, has estimated the difference at 3° of latitude; and the Gleditsia monosperma, the Catalpa, and the Aristolochia Sypho, and other vegetable productions, are found so many degrees farther to the north, in the basin of the Ohio, than on the coast of the Atlantic . M. Volney has endevoured to explain these phenomena by the frequency of the south-west winds, which drive back the warm air of the Gulf of Mexico towards these regions.

A series of good observations, made for seven years by Colonel Mansfield at Cincinnati, on the banks of the Ohio, and recently published by Mr Drake, in an excellent treatise on American meteorology , has removed the doubts which obscured this point.

The thermometrical means prove that the isothermal lines do not rise again in the regions of the west.

The quantity of heat which each point of the globe receives under the same parallels, is nearly equal on the east and the west of the Alleghany range, the winters being only a little milder to the west, and the summers a little warmer . The migrations of vegetables towards the north are favoured in the basin of the Mississippi, by the form and the direction of the valley which opens from the north to the south.

In the Atlantic Provinces, on the contrary, the valleys are transverse, and oppose great obstacles to the passage of plants from one valley to another.

This is true also of the Columbian Valley.

See Warden’s Account of the United States, vol. iii. p. 169.—Ed.

See my Essai sur la Geographie des Plantes, p. 154.

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

Cincinnati.—H. See Warden’s Account of the United States, vol. ii. 236 for an abstract of Mr Drake’s results.—Ed.

The following comparison of the mean temperatures has been deduced with great care.

I have taken for Philadelphia the means between the observations of Coxe and Rush. I have also referred for correction to the observations made by M. Legaux at Spring-Mill upon the Schuylkill, to the north of Philadelphia.

As Cincinnati is 512 feet above the level of the sea, its mean temperature is 1°.4 too low.– H.

Cincinnati. Lat. 36° 6′, west long. 84° 24′.

Winter, 32°.9 Fahr.

Spring, 54.1 Summer, 72.9 Autumn, 54.9 —— Mean, 53.7

Philadelphia. Lat. 39° 56′, west long. 75° 16′.

Winter, 32°.2 Fahr.

Spring, 51.4 Summer, 73.9 Autumn, 56.5 —— Mean, 53.5

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 Mississippi and the Missouri, it cannot be doubted that they rise again beyond the Rocky Mountains, on the opposite coast of Asia, between 35° and 55° of latitude.

To the considerations which I pointed out in my work on Mexico , are to be added the observations of Captain Lewis, and some other Anglo-American travellers, who have passed the winter on the banks of the Columbia.

In New California, they cultivate with success the olive, along the canal of Santa Barbara, and the vine from Monterey to the north of the parallel of 37°, which is that of Chesapeake Bay. At Nootka, in the Island of Quadra and Vancouver, and almost in the latitude of Labrador, the smallest rivers do not freeze before the month of January.

Captain Lewis saw the first frosts near the embouchure of the Colombia, only on the 7th of January, and the rest of the winter was rainy.

Through 122° 40′ of west long. the isothermal line of 50° Fahr. appears to pass almost as in the Atlantic part of the Old World, at 50° of lat.

The western coasts of the two worlds resemble one another to a certain point . But these returns of the isothermal lines do not extend beyond 60°.

The curve of 32° Fahr. is already found to the south of the Slave Lake, and it comes still farther south in approaching Lakes Superior and Ontario.

Essai Politique sur la Nouvelle Espagne, tom. ii. p. 440, 478, 509.

On account of the influence of west and south-west winds.

See Dalton’s Meteor. Observ. p. 125.

In advancing from Europe towards the east, the isothermal lines again descend , the number of fixed points being few.

We can only employ those which are made in places whose known elevation allows us to reduce the mean temperatures to the level of the sea.

The few good materials which we possess, have enabled us to trace the curves of 32° and 55°.

4. We know even the nodes of the latter curve round the whole 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 Foulweather to the S. of the embouchure of the Colombia, (lat. 44° 40′, W. long. 104°.)

Its nodes are distant at least 162° of longitude.

We have here pointed out only the empirical laws, under which are ranged the general phenomena, and the variations of the temperature which embrace at once a vast extent of the globe.

There are partial inflexions of the isothermal lines, which form, so to speak, particular systems modified by small local causes; such as the strange inflexion of the thermometric curves on the shores of the Mediterranean, between Marseilles, Genoa, Lucca and Rome , and those which determine the difference between the climate of the western coast and the interior of France.

These last depend much less on the quantity of heat received by a part of the globe during the whole year, than upon the unequal distribution of heat between winter and summer.

It will one day be useful to have upon particular charts the partial inflections of the isothermal lines, which are analogous to the lines of soundings or of equal declivity.

The employment of graphical representations will throw much light upon phenomena, which are deeply interesting to agriculturists.

If, in place of geographical charts, we possessed only tables containing the co-ordinates of latitude, longitude, and altitude, a great number of curious facts relative to the configuration and the superficial inequalities of continents would have remained forever unknown.

In comparing places from the west to the east, and nearly under the same parallel, we find, The elevation of Pekin is inconsiderable.

That of Moscow is 984 feet.

The absolute temperature of Madrid, to the west of Naples, is 59°; but the city is elevated 1978 feet above the level of the sea.—H.

West. Lat. Mean Temp. St Malo, 48° 39′ 54°.5 Amsterdam, 52 21 53.4 Naples, 40 50 63.3 Copenhagen, 55 41 45.7 Upsal, 59 52 41.9

East. Lat. Mean Temp. 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

Lat. Mean Temp. Bologna, 44° 29′ 56°.3 Genoa, 44 25 60.6

Lat. Mean Temp. Marseilles, 43° 17′ 58°.8 Rome, 41 53 60.4

H.

We have already found, that towards the north, the isothermal lines are neither parallel to the equator nor to one another; and it is on account of the want of parallelism, that we have, in order to simplify such complicated phenomena, traced round the whole globe the curves of equal heat.

The position of the line of 32° acts like the magnetic equator, whose inflexions in the South Sea modify the inclinations at great distances.

We may even believe that, in the distribution of climates, the line of 32° determines the position of the curve of greatest heat, which is as it were the isothermal equator, and that in America and Asia through 78° of west, and 102° of east longitude, the torrid zone commences more to the south of the tropic of Cancer, or that it there presents temperatures of less intensity.

An attentive examination of the phenomena proves that this is not the case.

Whenever we approach the torrid zone below the parallel of 30°, the isothermal lines become more and more parallel to one another, and to the earth’s equator.

The great colds of Canada and Siberia do not extend their action to the equatorial plains.

If we have long regarded the Old World as warmer between the tropics than the new world, it is, first, Because till 1760, travellers used thermometers of spirit of wine, coloured, and affected by light; 2d, Because they observed it either under the reflection of a wall, or too near the ground, and when the atmosphere was filled with sand; and, 3d, Because in place of calculating the true mean, they used only the thermometric maximum and minimum.

Good observations give,

Old World. Lat. Mean Temp. Senegambia, 15° 0 79°.07 Madras, 13 5 80 .42 Batavia, 6 12 80 .42 Manilla, 14 36 78 .08

New World. Lat. Mean Temp. Cumana, 10° 27′ 81°.86 Antilles, 17 0 81.05 Vera Cruz, 19 11 78.08 Havannah, 23 10 78.08

The mean temperature of the equator cannot be fixed beyond 81 [Formel] °.

Kirwan values it at 84°, but only two places of the earth were known, viz.

Chandernagor and Pondicherry, to which old travellers attributed annual temperatures above 81° [Formel] .

At Chandernagor, in latitude 21°.6, the mean temperature, according to Cotte, is 91°.9, but the Jesuite Boudier marked only the days when the thermometer was above 98°.6, and below 57°.2.

And at Pondicherry, in latitude 11° 55′, the mean temperature, according to Cotte, is 85°.3, and according to Kirwan, 88°; but M. de Cossigny observed with a spirit-of-wine thermometer.

The distribution of heat over different parts of the year differs, not only according to the decrease of the mean annual temperatures, but also in the same isothermal line.

It is this unequal division of the heat which characterises the two systems of climate of Europe and Atlantic America.

Under the torrid zone, a small number of months are warmer 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 been long known, that from the parallel of the Canary Isles to the Polar Circle, the severity of the winter augments in a progression much more rapid than the summers diminish in heat.

It is also known, that the climate of the islands and the coasts differs from that of the interior of continents, the former being characterised by mild winters and less temperate summers.

But it is the heat of summer particularly which affects the formation of the amylaceous and saccharine matter in fruits, and the choice of the plants that ought to be cultivated.

As the principal object of this memoir is to fix, after good observations, the numerical relations between the unequal quantities of heat distributed over the globe, we shall now compare the mean temperatures of three months of winter and summer under different latitudes, and shew how the inflections of the isothermal lines modify these relations.

In following the curves of equal heat from west to cast, from the Basin of the Mississippi to the eastern coasts of Asia, through an extent of 4000 leagues, we are struck with the great regularity which appears in the variations of the winter temperature.

I. Differences of the Seasons from the Equator to the Polar Circle.

Cisatlantic Region.

Long. 1° W. and 17° E. Transatlantic Region.

Long. 58°—72° W. Isothermal Lines of Mean Temperature.

Mean Temperature.

Winter.

Summer. Diff. Winter. Summer.

Diff. 68° 59°.0 80°.6 21°.6 53°.6 80°.6 27°.0 59 44.6 73.4 28.8 39.2 78.8 39.6 50 35.6 68.0 32.4 30.2 71.6 41.4 41 24.8 60.8 36.0 14.0 66.2 52.2 32 14.0 53.6 39.6 1.4 55.4 54.0

This table shews the increase of the difference between the winters and summers from 28° and 30° to the parallels of 55° and 65°.

The increase is more rapid in the Transatlantic Zone, where the isothermal lines of 32° and 50° approach one another very much; but it is remarkable, that in the two zones which form the two systems of different climates, the division of the annual temperature between winter and summer is made in such a manner, that, upon the isothermal line of 32°, the difference of the two seasons is almost double of that which is observed on the isothermal line of 68°.

Cisatlantic Region.

Long. 31° E. and 22° W. Places.

Latitude.

Mean Temperature.

Whole Year.

Winter.

Summer.

(Pondicherry)

11°.55 85°.3 77°.0 90°.5 Cairo, 30 02 72.7 57.7 84.7 Funchal, 32 37 68.7 63.9 72.5 Rome. 41 53 60.4 45.9 55.2 Bourdeaux, 44 50 56.5 42.1 70.7 Paris, 48 50 51.4 38.3 66.2 Copenhagen, 55 41 45.7 30.7 64.6 Stockholm, 59 20 42.3 25.5 61.9 Drontheim, 63 24 39.9 24.7 61.3 Umeo, 63 50 33.3 12.9 54.9

Transatlantic Region.

Long. 69° E. and 99° W Places.

Latitude.

Mean Temperature.

Whole Year.

Winter.

Summer.

Cumana, 10°.27 81°.9 81°.7 83°.7 Havannah, 23.10 78.1 71.2 83.3 Natchez, 31.28 64.8 48.6 79.2 Cincinnati, 39.06 53.6 32.9 72.9 Philadelphia, 39 56 54.9 32.2 73.9 New York, 40.40 53.8 29.8 79.2 Cambridge, 42.25 50.4 34.0 70.5 Quebec, 46.47 41.9 14.2 68.0 Nain, 57.10 26.4 0.6 48.4 Fort Churchhill, 59.02 25.3 6.8 52.2

If, instead of the mean temperatures of the seasons, we consider, I do not say the days of the maxima and minima of the year, which are the ordinates of the concave and convex summits of the entire curve, but the mean temperatures of the warmest and the coldest month, the increase of the differences becomes still more perceptible.

We request the reader to compare in the following Table only the places which belong to regions bounded by the same meridians, and consequently to the same system of climate; as for example, to the region of Eastern America to that of Western Europe, and that of Eastern Asia.

We must also attend to the changes of temperature produced by the monsoons in a part of the equinoctial regions, and distinguish under the temperate zone between the climate of the interior, or the continental climate, and that of islands and coasts.

Places. Lat. Mean Temperature.

Difference.

Observations.

Coldest Month.

Warmest Month.

Cumana, 10° 27 80°.1 84°.4 4°.3 Uninterrupted trade winds.

Pondicherry, 11 55 76.1 91.4 15.3 Monsoons.

Radiation of the sands.

Manilla, 14 36 68.0 86.9 18.9 Monsoons.

Vera Cruz, 19 11 70.0 81.7 11.7 North winds in winter.

Cape Français, 19 46 77.0 86.0 9.0 Uninterrupted trade winds.

Havannah, 23 10 70.0 83.8 13.8 North winds in winter.

Funchal, 32 37 64.0 75.6 11.6 Insular climate.

Natchez, 31 28 46.9 78.8 31.9 Transatlantic region.

Interior.

Cincinnati, 39 6 29.6 74.4 44.8 Same system of climate.

Pekin, 39 54 24.8 84.2 59.4 Region of eastern Asia.

Philadelphia, 39 56 29.8 77.0 47.2 Transatlant. region.

Eastern coasts New York, 40 40 25.3 80.8 55.5 Idem.

Rome, 41 53 42.1 77.0 34.9 Cisatlantic region.

Milan, 45 28 33.8 55.2 21.4 Interior land.

Buda, 47 29 27.7 71.6 43.9 Idem.

Paris, 48 50 35.1 69.8 34.7 Nearer the western coast.

Quebec, 46 47 14.0 73.4 59.4 Transatlant. region.

Eastern coasts . Dublin, 53 21 37.6 60.3 22.7 Region of the west of Europe.

Insular climate.

Edinburgh, 55 58 38.3 59.4 21.1 Idem.

Warsaw, 52 14 27.1 70.3 43.2 Interior land.

Petersburg, 5956 8.6 65.7 57.1 East of Europe.

North Cape, 71 0 22.1 46.6 24.5 Climate of coasts and islands.

We may conclude in general, that for any given place in the curves which express the annual temperatures, the ordinates of the concave and convex summits differ the more from one another, as the temperatures diminish.

In the New World, under 40° of latitude, we find a greater difference between the warmest and coldest months of the year than in the Old World, at Copenhagen and Stockholm under 56°—59° of latitude.

At Philadelphia the thermometer descends to 50° or 59° below the freezing point, while under the same parallel in Europe it descends scarcely 30°.6 below it.

I have endeavoured to shew, in another work, how this circumstance which characterises the regions which Buffon indicates by the name of Excessive Climates, influences the physical constitution of the inhabitants.

In the United States, the Europeans, and indeed all the natives, are, with great difficulty, inured to the climate.

After winters that have been very rigorous, not from the general temperature, but from an extreme depression of the thermometer, the irritability of the nervous system is prodigiously increased by the excessive heat of summer; and it is undoubtedly to this cause that we must, in a great measure, ascribe the difference in the propagation of the yellow fever, and the different forms of the marsh fever, under the equator, and in the temperate zone of the New World .

On high mountains in islands of little extent, and along the shores, the lines of annual temperature take nearly the same form as in warm climates, having only a less degree of curvature.

The difference between the seasons, too, becomes smaller.

At the North Cape, in 71° of latitude, and in the isothermal line of 32°, it is almost 11° greater than at Paris, in 49° of latitude, and in the isothermal line of 50°.

The sea-breezes and the fogs which render the winters so temperate, diminish at the same time the heats of summer . The characteristic of any climate is not the difference between the winters, expressed in degrees of the thermometer;—it is this difference, compared with the absolute quantities indicated by the mean temperature of the seasons.

Political Essay on the Kingdom of New Spain, tom. iv. p. 528.

Leopold von Buch’s Travels in Lapland, tom. ii.

II. Difference between the Winters and Summers, in following the same Isothermal Line from West to East.

The differences between the seasons of the year are less great near the convex summits of the isothermal curves, where these curves rise again towards the North Pole, than near the concave summits.

The same causes, which affect the inflexion or the greatest curvature of the isothermal lines, tend also to equalise the temperatures of the seasons.

The whole of Europe, compared with the eastern parts of America and Asia, has an insular climate, and, upon the same isothermal line, the summers become warmer, and the winters colder, in proportion as we advance from the meridian of Mont Blanc towards the east or the west.

Europe may be considered as the western prolongation of the old continent; and the western parts of all continents are not only warmer at equal latitudes than the eastern parts, but even in the zones of equal annual temperature, the winters are more rigorous, and the summers hotter on the eastern coasts than upon the western coasts of the two continents.

The northern part of China, like the Atlantic region of the United States, exhibits excessive climates, and seasons strongly contrasted, while the coasts of New California, and the embouchure of the Colombia, have winters and summers almost equally temperate.

The meteorological constitution of these countries in the N. W. resembles that of Europe as far as 50° or 52° of latitude; and without wishing to ascribe the great revolutions of our species solely to the influence of climate, we may affirm that the difference between the eastern and western shores of continents, has favoured the ancient civilisation of the Americans of the west,—facilitated their migrations towards the south, and multiplied those relations with eastern Asia, which appear in their monuments, their religion, traditions, and the division of the year.

In comparing the two systems of climates, the concave and convex summits of the same isothermal lines, we find at New York the summer of Rome and the winter of Copenhagen;—at Quebec the summer of Paris and the winter of Petersburg.

In China, at Pekin for example, where the mean temperature of the year is that of the coasts of Britanny, the scorching heats of summer are greater than at Cairo, and the winters as rigorous as at Upsal.

The mean temperature of the year being equal to the fourth part of the winter, spring, summer and autumnal temperatures, we shall have upon the same isothermal line of 53°6′ (12° cent.)

At the concave summit in America, 74° 40′ west long.

[Formel]

At the convex summit in Europe, 2° 20′ west long.

[Formel]

At the concave summit in Asia, 116° 20′ east long.

[Formel]

This analogy between the eastern coasts of Asia and America, sufficiently proves that the inequalities of the seasons, of which we have endeavoured to fix the numerical relations, depend on the prolongation and enlargement of continents towards the pole; of the size of seas in relation to their coasts, and on the frequency of the N. W. winds, which are the Vents de Remous of the temperate zone, and not on the proximity of some plateau or elevation of the adjacent lands.

The great plateaus of Asia do not stretch beyond 52° of latitude; and in the interior of the New Continent, all the immense basin bounded by the Alleghany Range, and the rocky mountains, and covered with secondary formations, is not more than from 656 to 920 feet above the level of the ocean, according to the levels taken in Kentucky, on the banks of the Monongahela, at Lake Erie .

Drake’s Nat. and Statist.

View of Cincinnati, p. 63.

The following table indicates for all the habitable temperate zone the division of the same quantity of annual heat between the two seasons of winter and summer.

The numbers which it contains, are either the result of direct observations, or of interpolations between a great number of observations made in neighbouring places, and situated under the same meridian.

We have followed each isothermal curve from west to east, giving the preference to places situated near the summits of the curve, as presenting at the same time the greatest differences in the distribution of the annual heat.

The longitudes are reckoned from the Observatory of Greenwich.

Isothermal Lines from 32° to 68°.

Long. Lat. Mean Temperature.

Winter.

Summer.

Isoth.

Line of 68°. 82° 10′ W. 29° 30 Florida, 53°.6 80°.6 1656 W. 3237 Madeira, 63.5 72.0 3 0 E. 3648 North Africa, 59.0 80.6 Isoth.

Line of 63°.5 8940 W. 3230 Mississippi, 46.4 77.0 1411 E. 4050 Italy, 50.0 77.0 Isoth.

Line of 59°.

8410 W. 3530 Basin of the Ohio, 39.2 77.9 3°—4° E. 4330 Middle of France, 44.6 75.2 Isoth.

Line of 54°.5 8440 W. 3830 America, W. of Allegh.

34.7 75.2 7410 W. 40 0 America, E. of ditto.

32.5 77.0 1 32 W. 4710 West of France, 39.0 68.0 9 20 E. 4530 Lombardy, 34.7 73.4 11620 E. 40 0 East of Asia, 26.6 82.4 Isoth.

Line of 50°.

8420 W. 4120 America , W. of Allegh.

31.1 71.6 7110 W. 4230 America , E. of ditto.

30.2 73.4 6 40 W. 5230 Ireland, 39.2 59.5 0 40 W. 5330 England, 37.4 62.6 2 20 E. 51 0 Belgium, 36.5 63.5 19 0 E. 4730 Hungary, 31.1 69.8 11620 E. 40 0 Eastern Asia, 23.0 78.8 Isoth.

Line of 45°.

5. 71 0 W. 4442 America , E. of Allegh.

23.9 71.6 2 10 W. 57 0 Scotland, 36.1 56.5 1235 E. 5540 Denmark, 30.3 62.6 2120 E. 53 5 Poland, 28.0 66.2 Isoth.

Line 41°.

7110 W. 47 0 Canada, 14.0 68.0 9 20 E. 6245 West of Norway, 24.8 62.6 1720 E. 6030 Sweden, 24.8 60.8 2420 E. 60 0 Finland, 23.0 63 5 36 20 E. 5830 Central Russia, 22.1 68.0 Isoth.

Line of 36°.

5. 71 40 W. 50 0 Canada, 6.8 60.8 18 5 E. 62 30 West coast of Gulf of Bothnia, 17.6 57.2 2220 E. 62 50 East coast of ditto.

16.5 59.0 Isoth.

Line of 32°.

5740 E. 53 0 Labrador, 3.2 51.8 1950 E. 65 0 Sweden, 11.3 53.6 2520 E. 71 0 North Extremity of Norway, 23.9 43.7

When we consider that the annual temperature of a place is nothing more than the numerical expression of the mean of the ordinates, we may imagine an infinity of entirely dissimilar curves, in which the twelve ordinates of the months have exactly the same mean.

This consideration should not lead us to believe, that a place which has the winter of the south of France, that is, where the mean temperature of winter is 44°.6, may, by the compensation of a summer and an autumn, much less warm, have the mean temperature of Paris.

It is true, that the constant ratio which is observed in the same parallel, between the solstitial heights of the sun and the semidiurnal arcs, is differently modified by the position of a place in the centre of a continent or upon the coast, by the frequency of certain winds, and by the constitution of an atmosphere more or less favourable to the transmission of light, and of the radiating caloric of the earth.

But these variations, which travellers have often exaggerated, have a maximum which nature never oversteps.

It is impossible to examine the preceding table without observing, that the division of the annual heat between summer and winter, follows on each isothermal line a determinate type; that the deviations of that type are contained between certain limits, and that they obey the same law in the zones which pass by the concave or convex summits of the isothermal lines, for example, by 58°—68° of West Long., and by 5°—7°, and 116° of East Longitude.

The following table shews the oscillations, or the maxima and minima, observed in the division of the heat between the seasons.

I have added the means of the winters and summers found at different degrees of longitude, and under the same isothermal line.

Isoth.

Lines.

Degrees of Long. examined.

Oscillations observed in the Means.

Means calculated.

Winters.

Summers.

Winters.

Summers.

32° 83 3°.2 to 24°.8 51°.8 to 53°.6 14°.0 52°.7 41 107 14.0 24.8 62.6 68.0 19.4 65.3 50 200 23.0 37.4 62.6 78.8 30.2 70.7 59 87 39.0 44.6 75.2 77.0 41.9 75.2 68 84 53.6 59.0 71.6 80.6 56.3 77.9

The deviations round the mean, that is, the inequality of the winters on the same isothermal line, increase in proportion as the annual heat diminishes, from Algiers to Holland, and from Florida to Pennsylvania.

The winters of the curve of 68° are not found upon that of 51°, and the winters of 51° are not met with on the curve of 42°.

In considering separately what may be called the same system of climate, for example, the European Region, the Transatlantic Region, or that of Eastern Asia, the limits of the variations become still more narrow.

Wherever in Europe, in 40° of longitude the mean temperature rises

To 59°.0 The winters are from 44°.6 to 46°.4 and the summers from 73°.0 to 75°.2 54.5 36.5 41.0 68.0 73.0 50.0 31.1 37.4 62.6 69.8 45.5 28.4 36.1 57.2 68.0 41.0 20.3 26.8 55 4 66.2

In tracing five isothermal lines between the parallels of Rome and Petersburg, the coldest winter presented by one of these lines is not found again on the preceding line.

In this part of the globe, those places whose annual temperature is 54° 5, have not a winter below 32°, which is already felt upon the isothermal line of 50°.

If, in place of stopping at the most rigorous winter which each curve presents, we trace the lines of equal winter temperature, (or the Isocheimal lines,) these lines, instead of coinciding with the lines of equal annual heat, oscillate round them.

As the Isocheimal lines unite points placed on different isothermal lines, we may examine to what distance their summits extend.

In considering always the same system of climates, for example, the European region, we shall find that the lines of equal winter cut isothermal lines, which are 9° distant.

In Belgium (in latitude 52°, and in isothermal latitude 51°8,) and even in Scotland, (in latitude 57°, and isothermal latitude 45° 5,) the winters are more mild than at Milan, (in latitude 45° 28′, and isothermal latitude 55° 8′,) and in a great part of Lombardy.

Farther to the north, in the Scandinavian Peninsula, we meet with three very different systems of climate, viz. 1. The region of the west coasts of Norway to the west of the mountains.

2. The region of the eastern coasts of Sweden, to the east of the mountains.

And, 3. The region of the west coasts of Finland, along the Gulf of Bothnia.

Baron Von Buch has made us acquainted with the atmospherical constitution of these three different regions, in which the slowest increase of the winter cold is felt from Drontheim to the North Cape, on the west and north-west coasts.

At the Isle of Mageroe, (in north lat. 82°,) at the northern extremity of Europe, under the parallel of 71°, the winters are still 7°.2 milder than at St Petersburg, (in north lat. 38°.8,) but the mean heat of the summers never reaches that of the winters of Montpellier, (in north lat. 59°.4).

At the Faroe Isles, under 62° of north lat. the lakes are very seldom covered with ice, and to so temperate a winter succeeds a summer, during which snow often falls upon the plains.

Nowhere without the tropics is the division of the annual heat among the seasons more equal.

In the temperate zone, under parallels nearer to our own, Ireland presents an example still more striking of the union of very mild winters, with cold and moist summers.

Notwithstanding a difference of 4° of latitude, the winters there are as mild as in Britain, while the mean temperature of the summers is three degrees less.

This is the true maritime climate.

The month of August, which on the same isothermal line, in the east of Europe , (in (Hungary) has the temperature of 71°.6, reaches only 60°.8 at Dublin.

The month of January, whose mean temperature at Milan, and in a great part of Lombardy, is only 35°.6, rises in Ireland to 5°.4, and 7°.2.

On the coasts of Glenarm, also (in north lat. 54° 56′,) under the parallel of Konigsberg, the myrtle vegetates with the same strength as in Portugal .

It scarcely freezes there in winter, but the heat of summer is not capable of ripening the vine.

Throughout all Holland, 90 days of winter have a mean temperature of from 36°.7 to 38°.

7. At Milan, at Padua, and at Verona, the same season is only from 34°.7 to 36°.

7. The observations made in Belgium and Holland, offer also a very remarkable example of an equal quantity of heat distributed in the space of a year over a vast extent of territory.

The mean temperatures scarcely vary from Paris to Franecker, over 3 [Formel] degrees of latitude, which, in the interior of a continent, should produce a difference of 3 [Formel] degrees of annual temperature.

The canal of the Channel opens towards the north.

The west winds blow, therefore, over a great part of the ocean, and during a long rainy winter, with the sky almost always clouded, the surface of the earth is less cooled by radiation than farther to the east, in the interior of the country, where the atmosphere is pure and dry.

The mean duration of the observations at each place is from eight to nine years, and 52,000 partial observations have been employed to obtain nine mean temperatures.

A similar harmony in the results is also found in Lombardy.

H.

Lat. Mean Temperature.

Year.

Winter.

Summer Franecker, 52° 36′ 51°.8 36°.7 67°.3 Amsterdam, 52 22 53.4 36.9 65.8 Hague, 52 3 51.8 38.3 65.5 Rotterdam, 51 54 51.1 36.9 64.9 Middelburg, 51 30 49.6 36.1 64.0 Dunkirk, 51 2 50.5 38.5 64.0 Brussels, 50 50 52.0 36.7 66.2 Arras, 50 17 49.4 35.8 63.3 Cambray, 50 10 52.0 39.0 66.6

Mean Temp.

Milan, 55°.8 Padua, 56.3 Verona, 55.8

Mean Temp.

Bologna, 56°.3 Venice, 56.5

Wahlenberg , Flora Carpath. p. 90.

Irish Transactions, tom. viii. p. 116, 203, 269.

These examples are sufficient to prove, that the isocheimal lines deviate much more than the isothermal lines from the terrestrial parallels.

In the system of European climates, the latitudes of two places that have the same annual temperature cannot differ more than from 4° to 5°, while two places whose mean winter temperature is the same, may differ more than 9° or 10 in latitude.

The farther we advance to the east, the more rapidly do these differences increase.

The lines of equal summer, or isotheral curves, follow a direction exactly contrary to the isocheimal lines.

We find the same summer temperature at Moscow, in the centre of Russia, and towards the mouth of the Loire, notwithstanding a difference of 11° of latitude.

Such is the effect of the radiation of the earth on a vast continent deprived of mountains.

It is sufficiently remarkable, that the inflexions of the isothermal lines, and the division of lands and seas are such upon the globe, that every where in North America, in Europe, and in Eastern Asia, the mean temperature of the summers does not denote more than 36° in the parallels of from 45° to 47°.

The same causes which in Canada, and in the north of China, sink the curves of equal annual heat, where the isothermal lines (those of 51°.8, and 53°.6,) corresponding to the parallels of 45° and 47°, tend to raise the lines of equal summer or the isotheral curves.

However great be the influence of the unequal division of the heat between the seasons, on the physical condition of nations, on the developement of agricultural industry, and the selection of plants for culture, I would not recommend the tracing upon the same chart the isothermal lines, and the winter and summer curves.

This combination would not be more fortunate than the lines of declination, inclination, and equal intensity of the magnetic forces, which, however, all depend upon one another.

Instead of multiplying the intersection of the curves, it will be sufficient to add to the isothermal lines, near their summits, the indication of the mean temperatures of summer and winter.

In this way, by following the line of 50°, we shall find marked in America, to the west of Boston, [Formel] , in England [Formel] , in Hungary [Formel] , and in China [Formel] .

(To be continued.)

On Isothermal Lines, and the Distribution of Heat Over the Globe.

By Baron Alexander de Humboldt.

(Continued from Vol. III. p. 274.)

After what has already been stated respecting the limits between which the annual heat divides itself on the same isothermal curve, it will be seen how far we are authorised to say, that the Coffee-tree, the Olive, and the Vine, in order to be productive, require mean temperatures of 64°.4; 60°.8, and 53°.6 Fahr.

These expressions are true only of the same system of climate, for example, of the part of the Old 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 annual temperatures, we determine also the nature of the summers and the winters.

It is known likewise, that the olive, the vine, the varieties of grain, and the fruittrees, require entirely different constitutions of the atmosphere.

Among our cultivated plants, some, slightly sensible of the rigours of winter, require very warm but not long summers; others require summers rather long than warm; while others, again, indifferent to the temperature of summer, cannot resist the great colds of winter.

Hence, it follows, that, in reference to the culture of useful vegetables, we must discuss three things for each climate,—the mean temperature of the entire summer,—that of the warmest month,—and that of the coldest month.

I have published the numerical results of this discussion in my Prolegomena de Distributione Geographica Plantarum, secundum Cœli Temperiem; and I shall confine myself at present to the limits of culture of the olive and the vine.

The olive is cultivated in our continent between the parallels of 36° and 44°, wherever the annual temperature is from 62°.6 to 58°.1, where the mean temperature of the coldest month is not below from 41°.0 to 42°.8, and that of the whole summer from 71°.6 to 73°.4 . In the New World, the division of heat between the seasons is such, that on the isothermal line of 58°.1, the coldest month is 35°.6, and that the thermometer sometimes sinks there even during several days from 14° to 10°.

4. The region of potable wines extends in Europe between the isothermal lines of 62°.6 and 50°, which correspond to the latitudes of 36° and 48°.

The cultivation of the vine extends, though with less advantage, even to countries whose annual temperature 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 conditions are fulfilled in Europe as far as the parallel of 50°, and a little beyond it.

In America, they do not exist farther north than 40°.

They have begun, indeed, some years ago to make a very good red wine to the west of Washington, beyond the first chain of mountains, in the valleys which do not extend beyond 38° 54′ of Lat.

On the Continent of Western Europe, the winters, whose mean temperature is 32°, do not commence till on the isothermal lines of 48°.2 and 50°, in from 51° to 52° of latitude; while in America, we find them already on the isothermal lines of from 51°.8 to 53°.6, under from 40° to 41° of latitude.

In cases like the present, we have not used the round numbers of Fahrenheit, as is done in the original with the Centigrade scale, but have given the real value of the degrees used by the author, that his exact numbers may always be ascertained.—Ed.

If, instead of considering the natural inflexions of the isothermal lines, that is to say, those that propagate themselves progressively at great intervals of longitude, we direct our attention to their partial inflexions, or to particular systems of climates occupying a small extent of country, we shall still find the same variations in the division of the annual heat between the different seasons.

These partial inflexions are most remarkable,

1st, In the Crimea, where the climate of Odessa is contrasted with that 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 Isles to Nice and Bordighera, (Annales du Museum, tom. xi. p. 219.), where the small maritime palm-tree, Chamærops, grows wild, and where the date-tree is cultivated on a large scale, not to obtain its fruit, but the palms or etiolated leaves.

3dly, In England, on the coast of Devonshire, where the port of Salcombe has, on account of its temperate climate, been called the Montpellier 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.

Knight, Trans. Hort. Soc. vol. i. p. 32.

In 1774, an Agave flowered at Salcombe, 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 on espaliers, which are sheltered, as at Rome, only by means of a matting.—H.

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 aloifolia, the Erica Mediterranea, the Hortensia, the Fuchsia, the Dahlia, resist in open ground the inclemency of a winter which lasts scarcely fifteen or twenty days, and which succeeds to a summer by no means warm.

During this short winter, the thermometer sometimes falls to 17°.

6. The sap ascends in the trees from the month of February; but it often freezes even in the middle of May.

The Lavatera arborea is found wild in the isle of Glenans, and opposite to this island, on the continent, the Astragalus Bajonensis, and the Laurus nobilis .

Bonnemaison, Geogr.

Botan. du Depart. du Finisterre, (Journal de Botan. tom. iii. p. 118.)

From observations made in Brittany for twelve years, at St Malo, at Nantes, and at Brest, the mean temperature of the peninsula appears to be above 56°.3.

In the interior of France, where the land is not much elevated above the sea, we must descend 3° of latitude in order to find an annual temperature like this.

It is known from the researches of Arthur Young , that in spite of the great rise of the two isothermal lines of 53°.6 and 55°.4 on the western coast of France, the lines of culture (those of the olive, and of the maize and vine,) have a direction quite opposite, from S.W. to N.E. This phenomenon has been ascribed , with reason, to the low temperature of the summers along the coast; but no attempt has been made to reduce to numerical expressions the ratios between the seasons in the interior and on the coast.

In order to do this, I have chosen eight places, some of which lie under the same geographic parallels, and others in the prolongation of the same isothermal line.

I have compared the temperatures of winter, of summer, and of the warmest months; for a summer of uniform heat excites less the force of vegetation, than a great heat, preceded by a cold season.

The terms of comparison have been along the Atlantic; the coasts of Brittany, (from St Malo and St Brieux to Vannes and Nantes); the sands of Olonne; the Isle of Oleron; the embouchure of the Garonne and Dax, in the department of the Landes; and in the interior, corresponding to the same parallel, Chalons sur Marne, Paris, Chartres, Troyes, Poitiers, and Montauban.

Farther south, from 44 [Formel] ° of Lat. the comparisons become incorrect, because France, locked between the Ocean and the Mediterranean, presents, along this last basin, in the fine region of the olives, a system of climate of a particular kind, and very different from that of the western coast.

Travels in France, vol. ii. p. 91.

The line which limits the cultivation of the vine, extends from the embouchure of the Loire and of the Vilaine, by Pontoise, to the confluence of the Rhine and the Moselle.

The line of the olive trees commences to the west of Narbonne, passes between Orange and Montelimart, and carries itself to the N.E. in the direction of the Great St Bernard.—H.

Decandolle, Flor. Franç.

3d edit. tom. ii. pl. viii.

xi. Lequinio, Voy. dans. le Jura, tom. ii. p. 84.—91.

Places in the Interior.

Latitude.

Mean Temperature Of the Year.

Of Winter.

Of Summer.

Of the Warmest Month.

Fahr.

Fahr.

Fahr.

Fahr.

Chalons sur Marne, ‒ 48°.57 50°.5 36°.1 66°.6 67°.5 Paris, ‒ ‒ ‒ 48.50 51.1 38.7 65.3 67.5 Chartres, ‒ ‒ 48.26 50.7 37.0 64.6 65.7 Troyes, ‒ ‒ 48.18 52.2 38.3 67.3 68.4 Chinon, ‒ ‒ 47.26 53.4 38.7 69.1 70.2 Poitiers, ‒ ‒ 46.39 54.3 39.7 67.1 69.3 Vienne, ‒ ‒ 45.31 55.0 38.7 71.6 73.4 Montauban, ‒ 44.01 55.6 42.6 69.3 71.4 Places on the Coast.

St Malo, ‒ ‒ 48°.39′ 55°.5 42°.4 66°.9 67°.5 St Brieux, ‒ ‒ 48.31 52.3 41.7 64.4 67.1 Vannes, ‒ ‒ 47.39 51.8 39.7 64.4 65.8 Nantes, ‒ ‒ 47.13 54.7 40.5 68.5 70.5 La Rochelle, ‒ ‒ 46.14 53.1 40.3 66.6 67.1 Oleron, ‒ ‒ 45.55 58.1 44.6 68.5 72.1 Bourdeaux, ‒ ‒ 44.50 56.5 42.1 70.9 71.4 Dax, ‒ ‒ ‒ 43.52 54.1 44.4 67.3 68.9

These results are deduced from 127,000 observations, made with sixteen thermometers, of, no doubt, unequal accuracy.

In supposing, on the theory of probabilities, that in such a number of observations, the errors, in the construction and exposure of the instruments, and in the hours of observation, will, in a great measure, destroy one another, we may determine, by interpolation, either under the same parallel, or upon the same isothermal line, the mean winters and summers of the interior and of the coast of France.

This comparison gives,—

Mean Winter.

Mean Summer. I. Isothermal Lines 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 of France; that is to say, as the mean temperature of the year becomes there greater than under the same latitude in the interior of the country, we ought to expect, that in advancing from east to west under the same parallel, the heat of the summers would not diminish.

But the rising, again, of the isothermal lines, and the proximity of the sea, tend equally to increase the mildness of the winters; and each of these two causes acts in an opposite manner upon the summers.

If the division of the heat between these seasons was equal in Brittany and in Orleannois, in the climate of the coast, and the continental climates, we ought to find the winters and summers warmer in the same latitude along the coast.

In following the same isothermal lines, we readily observe, in the preceding table, that the winters are colder in the interior of the country, and the summers more temperate upon the coasts.

These observations confirm in general the popular opinion respecting the climate of coasts; but in recollecting the cultivation and the developement of vegetation on the coasts and in the interior of France, we should expect differences of temperature still more considerable.

It is surprising that these differences between the winter and the summer should not exceed 1°.8, or nearly a quarter of the difference between the mean temperature of the winters or the summers of Montpellier and Paris.

In speaking of the limits of the cultivation of plants upon mountains, I shall explain the true cause of this apparent contradiction.

In the mean time, it may be sufficient to remark, that our meteorological instruments do not indicate the quantity of heat, which, in a clear and dry state of the air, the direct light produces in the more or less coloured parenchyma of the leaves and fruits.

In the same mean temperature of the atmosphere, the developement of vegetation is retarded or accelerated, according as the sky is foggy or serene, and according as the surface of the earth receives only a diffuse light, during entire weeks, or is struck by the direct rays of the sun.

On the state of the atmosphere, and the degree of the extinction of light, depend, in a great measure, those phenomena of vegetable life, the contrasts of which surprise us in islands, in the interior of continents, in plains, and on the summit of mountains.

If we neglect these photometrical considerations, and do not appreciate the production of heat in the interior of bodies, and the effect of nocturnal radiation in a clear or a cloudy sky, we shall have some difficulty in discovering, from the numerical ratios of the observed summer and winter temperatures of Paris and London, the causes of the striking difference which appears in France and England in the culture of the vine, the peach, and other fruit-trees .

Young’s Travels in France, vol. ii. p. 195.

When we study the organic life of plants and animals, we must examine all the stimuli or external agents which modify their vital actions.

The ratios of the mean temperatures of the months are not sufficient to characterise the climate.

Its influence combines the simultaneous action of all physical causes; and it depends on heat, humidity, light, the electrical tension of vapours, and the variable pressure of the atmosphere.

It is the last cause which, on the tops of mountains, modifies the perspiration of plants, and even increases the exhaling organs.

In making known the empirical laws of the distribution of heat over the globe, as deducible from the thermometrical variations of the air, we are far from considering these laws as the only ones necessary to resolve all the problems of climate.

Most of the phenomena of nature present two distinct parts, one which may be subjected to exact calculation, and another which cannot be reached but through the medium of induction and analogy.

Having considered the division of heat between winter and summer on the same isothermal line, we shall now point out the numerical ratios between the mean temperature of spring and winter, and between that of the whole year and the warmest month.

From the parallel of Rome to that of Stockholm, and consequently between the isothermal lines of 60°.8 and 41°, the difference of the months of April and May is everywhere 10°.8 or 12°.6, and all the successive months are those which present the most rapid increase of temperature.

But, as in northern countries, in Sweden, for example, the month of April is only 37°.4, the 10°.8 or 12°.6 which the month of May adds , necessarily produces there a much greater effect on the developement of vegetation than in the south of Europe, where the mean temperature of April is from 53°.6 to 55°.

4. It is from an analogous cause, that in passing from the shade to the sun, either in our climates in winter, or between the tropics on the back of the Cordilleras, we are more affected by the difference of temperature than in summer and in the plains, though in both cases the thermometrical difference is the same, for example from 5°.4 to 7°.2.

Near the polar circle, the increase of the vernal heat is not only more sensible, but it extends equally to the month of June.

At Drontheim, the temperatures of April and May, like those of May and June, differ not 10°.8 or 12°.6, but 14°.4 or 16°.2.

In calculating for Europe, from 46° to 48° of Lat. for ten years the mean temperatures of every ten days, we find, that the decades which succeed one another, differ near the summits of the annual curve only 1°.44, while the differences rise in autumn from 3°.6 to 5°.4, and in spring from 5°.4 to 7°.

2.—H.

In distinguishing upon the same isothermal line the places which approach its concave or convex summits, in the same system of climates in the northern and southern regions, we shall find,

1st, That the increase of the vernal temperature is great, (from 14°.4 or 16°.2, in the space of a month), and equally prolonged, wherever the division of the annual heat between the seasons is very unequal, as in the north of Europe, and in the temperate part of the United 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, (scarcely 7°.2), and equally prolonged, wherever there is an insular climate.

4thly, That in every system of climates, in the zones contained between the same meridians, the vernal increase is smaller, and less equally prolonged, in low than in high latitudes.

The isothermal zone from 53°.6 to 55°.4, may serve as an example for confirming these different modifications of spring.

In Eastern Asia, near the concave summit, the differences of temperature between the four months of March, April, May and June, are very great, and very equal, (15°.7, 13°.3, and 13°.9).

In advancing westward towards Europe, the isothermal line rises again, and in the interior of the country, near the convex summit, the increase is still greater, but little prolonged; that is to say, that of the four months which succeed one another, there are only two whose difference rises to 13°: they are 9°.4; 13°.3; 4°.1.

Farther west, on the coasts, the differences become small and equal, viz.

3°.6; 6°.5; 5°.6.

In crossing the Atlantic, we approach the western concave summit of the isothermal line of 53°.

6. The increase of vernal temperature shews itself anew, and almost as great, 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 the curve of annual temperature, the spring and autumn mark the transitions from the minimum and the maximum.

The increments are naturally slower near the summits than in the intermediate part of the curve.

Here they are greater, and of longer continuance, in proportion to the difference of the extreme ordinates.

The autumnal decrease of temperature is less rapid than the vernal increase, because the surface of the earth acquires the maximum of heat slower than the atmosphere, and because, in spite of the serenity of the air which prevails in autumn, the earth loses slowly, by radiation, the heat which it has acquired.

The following Table will shew how uniform the laws are which I have just established.

Names of Places.

Latitude.

March. April. May. June.

Differences of Temperature of the Four Months.

Mean Temp.

of the Year. I. Group,—Concave Summits in America.

Natchez, ‒ ‒ ‒ 31° 28′ 57°.9 66°.2 72°.7 79°.5 8°.3 6°.1 7°.2 64°.8 Williamsburg, ‒ ‒ 37 18 46.4 61.2 66.6 77.7 14.8 5.4 11.2 58.1 Cincinnati, ‒ ‒ 39 0 43.7 57.4 61.2 70.9 13.7 3.6 9.7 53.8 Philadelphia, ‒ ‒ 39 56 44.1 53.6 62.1 72.3 9.5 8.5 10.3 53.6 New York, ‒ ‒ 40 40 38.7 49.1 65.8 80.2 10.4 16.7 14.4 53.8 Cambridge, ‒ ‒ 42 25 34.5 45.5 56.8 70.2 11.0 11.3 13.3 50.4 Quebec, ‒ ‒ ‒ 46 47 23.0 39.6 54.7 63.9 16.6 15.1 41.2 41.7 Nain, ‒ ‒ ‒ 57 0 6.8 27.5 37.0 43.3 20.7 9.5 8.1 26.4 II. Group,—Convex Summits in Europe.

1. Continental Climate: Rome, ‒ ‒ ‒ 41 53 50.4 55.4 66.9 72.3 5.0 11.5 5.4 60.4 Milan, ‒ ‒ ‒ 45 28 47.8 51.1 65.1 70.5 7.7 9.5 5.4 55.8 Geneva, ‒ ‒ ‒ 46 12 39.6 45.5 58.1 62.2 6.1 12.4 4.1 49.3 Buda, ‒ ‒ ‒ 47 29 38.3 49.1 64.8 68.4 10.8 15.7 3.6 51.1 Paris, ‒ ‒ ‒ 48 50 42.3 48.2 60.1 64.4 8.5 11.9 4.3 51.1 Gottingen, ‒ ‒ 51 32 34.2 44.2 57.7 62.2 10.1 13.5 4.5 46.9 Upsal, ‒ ‒ ‒ 59 51 29.5 39.7 48.7 57.9 10.3 9.0 9.2 41.9 Petersburg, ‒ ‒ 59 56 27.5 37.0 50.2 59.4 9.5 13.1 9.2 38.8 Umeo, ‒ ‒ ‒ 63 50 23.0 34.2 43.7 55.0 11.2 9.5 11.3 33.3 Uleo, ‒ ‒ ‒ 65 0 14.0 26.2 41.0 55.0 12.2 14.8 14.0 33.1 Enontekies, ‒ ‒ 68 30 11.5 26.6 36.5 49.5 15.1 9.9 13.0 27.0 2. Climate of the Coast: Nantes, ‒ ‒ ‒ 47 13 50.0 53.6 60.1 65.7 3.6 6.5 5.6 54.7 London, ‒ ‒ ‒ 51 30 44.2 49.8 56.5 63.1 5.6 6.7 6.7 51.6 Dublin, ‒ ‒ ‒ 53 21 41.9 45.3 51.8 55.6 3.4 6.5 4.0 48.4 Edinburgh, ‒ ‒ 55 57 41.4 47.3 50.5 57.2 5.8 3.2 6.7 47.8 North Cape, ‒ ‒ 71 0 25.0 30.0 34.0 40.1 5.2 4.0 6.1 32.0 III. Group,—Concave Summit of Asia.

Pekin, ‒ ‒ ‒ 39 54 41.4 57.0 70.3 84.2 15.7 13.3 13.9 54.9

In all places whose mean temperature is below 62°.6, the revival of nature takes place in spring, in that month whose mean temperature reaches 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.

Cotte, Meteorologie, p. 448.—Wahlenberg, Flor.

Lap.

Pl. 51.

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 temperature of 51°.

8. Near the Hospice of St Gothard, the birch cannot vegetate, as the warmest month of the year there scarcely reaches 46°.

5. Barley, in order to be cultivated advantageously, requires , during ninety days, a mean temperature of from 47°.3 to 48°.

2. By adding the mean temperatures of the months above 51°.8, that is, the temperatures of those in which trees vegetate that lose their foliage, we shall have a sufficiently exact mean of the strength and continuance of vegetation.

As we advance towards the north, vegetable life is confined to a shorter interval.

In the south of France, there are 270 days of the year in which the mean temperature exceeds 51°.8; that is to say, the temperature which the birch requires to put forth its first leaves.

At St Petersburgh, the number of these days is only 120. These two cycles of vegetation, so unequal, have a mean temperature which does not differ more than 5°.4; and even this want of heat is compensated by the effects of the direct light, which acts on the parenchyma of plants in proportion to the length of the days.

If we compare, in the following Table, Eastern Asia, Europe, and America, we shall discover, by the increase of heat during the cycle of vegetation, the points where the isothermal lines have their concave summits.

The exact knowledge of these cycles, will throw more light on the problem of Agricultural Geography, than the examination of the single temperatures of summer.

Playfair, Edin.

Trans, vol. v. p. 202.— Wahlenberg in Gilbert’s Annalen, tom. xli. p. 282.

Lines of Equal Heat.

Names of Places.

Latitude.

Mean Temp.

of the Year.

Sum of the Mean Temp. of the Months that reach 51°.8.

Number of those Months.

Mean Temperat.

of the days which reach 51°.

8. Mean Temperature of the warmest Months.

Observations.

Isothermal Line of 59°.0, Rome, ‒ 41° 53′ 60°.4 585° 9 64°.8 77°.0 Basin of the Mediterranean.

Nismes, 43 50 60.3 593 9 65.8 78.3 Idem.

Isothermal Line of 53°.6, Pekin, ‒ 39 54 54.9 499 7 71.2 84.2 Eastern concave summit.

Poitiers, 46 34 54.3 426 7 60.8 69.3 Convex summit.

Nantes, 47 13 54.7 438 7 62.6 69.8 Idem, coasts.

St Malo, 48 39 53.8 431 7 61.5 68.4 Idem.

Philadelphia, 39 56 53.4 463 7 66.2 77.0 Western concave summit.

Cincinnati, 39 6 53.8 458 7 65.5 74.3 Idem.

Isothermal Line of 50°.0, London, 51 30 51.8 364 6 60.6 66.6 Insular climate.

Paris, ‒ 48 50 51.1 381 6 63.5 69.8 Near the coasts.

Buda, ‒ 47 29 51.1 323 5 64.6 72.0 Interior.

Isothermal Line of 48°.2, Geneva, 46 12 49.3 311 5 62.2 66.6 Interior.

Dublin, 53 21 48.7 282 5 56.5 60.8 Climate of the coasts.

Edinburgh, 55 57 47.8 279 5 55.8 59.4 Idem.

Isothermal Line of 41°.0, Upsal, ‒ 59 51 41.9 229 4 57.2 61.9 Convex summit.

Quebec, 46 47 41.7 318 5 63.7 73.4 Western concave summit.

Isothermal Line of 32°.0, Petersburgh, 59 56 38.8 236 4 59.0 65.7 East of Europe.

Umeo, ‒ 53 50 33.3 118 2 59.0 62.6 E. Coast of Gulf of Bothnia.

North Cape, 71 0 32.0 0 0 0 46.6 Interior climate.

Enontekies, 68 30 27.0 116 2 58.1 59.5 Continental climate.

In the system of European climates, from Rome to Upsal, between the isothermal lines of 59° and 41°, the warmest month adds from 16°.2 to 18° to the mean temperature of the year.

Farther north, and also in eastern Asia, and in America, where the isothermal lines bend towards the equator, the increments are still more considerable.

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 mean temperature is equal to that of the whole year.

From the mean of ten observations, this temperature of the year is found at Buda in Hungary from the 15th to the 20th of April, and from the 18th to the 23d of October.

The ordinates of the other decades may be regarded as functions of the mean ordinates.

In considering the temperatures of entire months, we find, that to the isothermal line of 35°.6, the temperature of the month of October coincides (generally within a degree) with that of the year.

The following Table proves that it is not the month of April, as Kirwan affirms, (Estimate, &c. p. 166.), that approaches nearest to the annual temperature.

Names of Places.

Mean Temperature Of the Year.

Of October.

Of April. Cairo, ‒ 72°.3 72°.3 77°.9 Algiers, ‒ 69.8 72.1 62.6 Natchez, 65.0 68.4 66.4 Rome, ‒ 60.4 62.1 55.4 Milan, 55.8 58.1 55.6 Cincinnati, 53.6 54.9 56.8 Philadelphia, 53.4 54.0 53.6 New York, 53.8 54.5 49.1 Pekin, ‒ 54.7 55.4 57.0 Buda, ‒ 51.1 52.3 49.1 London, ‒ 51.8 52.3 49.8 Paris, ‒ 51.1 51.3 48.2 Geneva, ‒ 49.3 49.3 45.7 Dublin, ‒ 48.6 48.7 45.3 Edinburgh, 47.8 48.2 46.9

Names of Places.

Mean Temperature Of the Year.

Of October.

Of April.

Gottingen, 46°.9 47°.1 44°.4 Franeker, 52.3 54.9 50.0 Copenhagen, 45.7 48.7 41.0 Stockholm, 42.3 42.4 38.5 Christiania, 42.6 39.2 42.6 Upsal, ‒ 41.7 43.3 39.7 Quebec, 41.9 42.8 39.6 Petersburgh, 38.8 39.0 37.0 Abo, ‒ 41.4 4.0 40.8 Drontheim, 39.9 39.2 34.3 Uleo, ‒ 33.1 37.9 34.2 Umeo, ‒ 33.3 37.8 34.0 North Cape, 32.0 32.0 30.2 Enontekies, 27.0 27.5 26.6 Nain, ‒ 26.4 33.1 27.5

As travellers are seldom able to make observations for giving immediately the temperature of the whole year, it is useful to know the constant ratios which exist in each system of climates, between the vernal and autumnal temperatures, and the annual temperature.

The quantity of heat which any point of the globe receives, is much more equal during a long series of years than we would be led to believe from the testimony of our sensations, and the variable product of our harvests.

In a given place, the number of days during which the N.E. or S.W. winds blow, preserve a very constant ratio, because the direction and the force of these winds, which bring warmer or colder air, depend upon general causes,—on the declination of the sun,—on the configuration of the coast,—and on the lie of the neighbouring continent.

It is less frequently a diminution in the mean temperature, than an extraordinary change in the division of the heat between the different months, which occasions bad harvests.

By examining between the parallels of 47° and 49° a series of good meteorological observations, made during ten or twelve years, it appears, that the annual temperatures vary only from 1°.8 to 2°.7; those of winter from 3°.6 to 5°.4; those of the months of winter from 9° to 10°.

8. At Geneva, the mean temperatures of twenty years were as follows:

Mean Mean Years.

Temp. Years. Temp. 1796, 49°.3 1806, 51°.4 1797, 50.5 1807, 49.3 1798, 50.0 1808, 46.9 1799, 48.7 1809, 48.9 1800, 50.5 1810, 51.1 1801, 51.1 1811, 51.6 1802, 50.9 1812, 47.8 1803, 50.4 1813, 48.6 1804, 51.1 1814, 48.2 1805, 47.8 1815, 50.0 Mean of 20 Years, 49°.67

If, in our climates, the thermometrical oscillations are a sixth part of the annual temperature, they do not amount to one twenty-fifth part under the tropics.

I have computed the thermometrical variations, during eleven years, at Paris, for the whole year, the winter, the summer, the coldest month, the warmest month, and the month which represents most accurately the annual mean temperature; and the following are the results which I obtained:

Observations of M. Bouvard.

Mean Temperature Of the Year.

Of Winter.

Of Summer.

Of January.

Of August.

Of October.

Paris, 1803, ‒ 51°.1 36°.7 67°.6 34°.3 67°.6 50°.5 1804, ‒ 52.0 41.0 65.5 43.9 64.6 52.7 1805, ‒ 49.5 36.0 63.1 34.9 64.8 49.3 1806, ‒ 53.4 40.6 65.3 43.0 64.6 51.8 1807, ‒ 51.4 42.3 67.8 36.1 70.5 54.3 1808, ‒ 50.5 36.7 66.2 36.3 66.6 48.2 1809, ‒ 50.9 40.5 62.4 40.8 64.2 49.6 1810, ‒ 50.9 36.5 63.3 30.6 63.7 52.9 1811, ‒ 52.7 39.2 65.1 26.6 63.7 57.6 1812, ‒ 49.8 39.6 63.1 34.7 64.2 51.1 1813, ‒ 49.8 36.1 61.7 32.5 62.6 53.1 Mean of these 11 years, 51°.1 38°.7 64°.0 36°.6 65°.1 51°.9

At Geneva, the mean temperatures of the summers were, from 1803 to 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 last of which was so destructive to the crops in a great part of France, the difference of the mean annual temperature was only 2°, and that of the 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 oscillations round the mean did not go beyond — 2°.9, and +3°4.

In comparing places which belong to the same system of climates, though more than eighty leagues distant, the variations seem to be very 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.

Mean Annual Temperature.

Difference between Mean Ann. Temp. and that for 12 years, 51°.1 Mean Annual Temperature.

Difference between Mean An. Temp. and that of 12 years, 49°.

6. Mean Temperature of Winter.

Difference with the mean Winter Temperature of 12 years, 38°.

7. Mean Temperature of Winter.

Difference with the Mean Winter Temperature of 12 years, 34°.

9. Mean Temperature of Summer.

Difference with the Mean Temrature of Summer for 12 years, 64°.

6. Mean Temperature of Summer.

Difference with the Mean Temperature of Summer 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 63.5 — 1.4 1809, 50.9 — 0.2 48.7 — 0.9 40.5 + 1.8 35.1 + 0.2 62.4 — 2.2 63.1 — 1.8 1810, 50.9 — 0.2 51.1 + 1.5 36.5 — 2.2 63.3 — 1.3 1811, 52.7 + 1.6 51.8 + 2.2 39.2 + 0.5 65.1 + 0.5 1812, 49.8 — 1.3 47.8 — 1.8 39.6 + 0.9 63.1 — 1.5 1813, 49.8 — 1.3 48.6 + 1.0 36.1 — 2.6 61.7 — 2.9

(To be continued in next Number.)

On Isothermal Lines, and the Distribution of Heat over the Globe.

By Baron Alexander de Humboldt.

(Continued from Vol. IV. p. 37.)

All the ratios of temperature which we have hitherto fixed, belong to that part of the lower strata of the atmosphere which rests on the solid surface of the globe in the northern hemisphere.

It now remains for us to discuss the temperature of the southern hemisphere.

In few parts of natural philosophy, have naturalists differed so widely in opinion.

From the beginning of the 16th century, and the first navigations round Cape Horn, an idea prevailed in Europe, that the southern was considerably colder than the northern hemisphere.

Mairan and Buffon combated this opinion by inaccurate reasonings of a theoretical nature.

Æpinus established it anew.

The discoveries of Cook made known the vast extent of ice round the South Pole; but the inequality in the temperature of the two hemispheres was then exaggerated.

Le Gentil, and particularly Kirwan , had the merit of having first demonstrated, that the influence of the circumpolar ice extended much less into the temperate zone than was generally admitted.

The less distance of the sun from the winter solstice, and his long continuance in the northern signs, act in an opposite manner on the heat in the two hemispheres; and as (after the theorem of Lambert) the quantity of light which a planet receives from the sun, increases in proportion to the true anomaly, the inequality in the temperature of the two hemispheres is not the effect of unequal radiation.

The southern hemisphere receives the same quantity of light; but the accumulation of heat in it is less §, on account of the emission of the radiant heat which takes place during a long winter.

This hemisphere being also in a great measure covered with water, the pyramidal extremities of the continents have there an irregular climate.

Summers of a very low temperature are succeeded, as far as 50° of south latitude, by winters far from rigorous.

The vegetable forms also of the torrid zone, the arborescent ferns, and the orchideous parasites, advance towards 38° and 42° of S. Latitude.

The small quantity of land in the southern hemispheres, contributes not only to equalise the seasons, but also to diminish absolutely the annual temperature of that part of the globe.

This cause is, I think, much more active than that of the small eccentricity of the earth’s orbit.

The continents during summer radiate more heat than the seas, and the ascending current which carries the air of the equinoctial and temperate zones towards the circumpolar regions, acts less in the southern than in the northern hemisphere.

That cap of ice which surrounds the pole to the 71st and 68th degree of south latitude, advances more towards the equator, whenever it meets a free sea; that is, wherever the pyramidal extremities of the great continents are not opposite to it.

There is reason to believe, that this want of dry land would produce an effect still more sensible, if the division of the continents was as unequal in the equinoctial as in the temperate zones .

Theorie de la Terre, tom. i. p. 312.—Mémoires de l’Acad. 1765, p. 174.

De Distributione Caloris, 1761.

Estimate, &c. p. 60.—Irish Trans. vol. viii. p. 423.—Le Gentil, Voyage dans l’Inde, vol. i. p. 73.

Mairan, Mem. Acad. 1765, p. 166.—Lambert, Pyrometrie, p. 310. Prevost, De la Chalcur Rayonnante, 1809, p. 329. & 367. § 280,—306.

The dry lands in the two hemispheres are in the ratio of 3 to 1.

The dry lands between the tropics, are in the two hemispheres as 5 to 4, and without the tropies as 13 to 1.

Theory and experience prove, that the difference of temperature between the two hemispheres, cannot be great near the limit which separates them . Le Gentil had already observed, that the climate of Pondicherry is not warmer than that of Madagascar at the Bay of Antongel in 12° of S. Lat. Under the parallels of 20 the Isle of France has the same annual temperature, viz. 80°.1, as Jamaica and St Domingo.

The Indian Sea between the east coasts of Africa, the Isles of Sonde and New Holland, form a kind of gulf which is shut up to the north by Arabia and Hindostan.

The isothermal lines there appear to go back to the South Pole; for farther to the west in the open sea between Africa and the New World, the cold of the southern hemisphere already causes itself to be felt from the 22d degree, on account of its insulated mountains and particular localities.

1 shall not mention the island of St Helena, Lat. 15° 55′ whose mean temperature, according to the observations of M. Beatson, at the sea side, does not exceed 71°6 or 73°4. It is the eastern coast of America, which, in the observations of a Portuguese astronomer, M. Benito Sanchez Dorta , present us with the S. Lat. of 22° 54′, almost at the limit of the equinoctial region with a plan, of which we know the climate by more than 3500 thermometrical and barometrical observations made every year, to ascertain the horary variations in the heat and pressure of the air.

The mean temperature of Rio Janeiro is only 74°.3, whilst, notwithstanding the north winds which bring the cold air of Canada during winter into the Gulf of Mexico, the mean temperatures of Vera Cruz, (Lat. 19° 11′,) and of the Havannah, (Lat. 23° 10′,) are 77°.

9. The differences of the two hemispheres become more sensible in the warmest months.

Prevost, p. 343.

Mem. de l’Acad. de Lisbonne, tome ii. p. 348. 369.

Rio Janeiro.

Havannah.

Mean Temp.

Mean Temp.

June, 68°.0 December, 71°.8 July, 70 2 January, 70 2 January, 79 2 July, 83 3 February, 80 6 August, 83 8

The great equality in the divısion of the annual heat in 34° of N. and S. Lat. is very surprising.

If we attend to the three continents of New Holland, Africa and America, we shall find, that the mean temperature of Port Jackson, (Lat. 33° 51′,) is, after the observations of MM.

Hunter, Peron, and Freycinet, ‒ ‒ ‒ 66°.7

That of the Cape of Good Hope, (Lat. 33° 53′,) 66 9

That of the city of Buenos Ayres, (Lat. 34° 36′,) 67 5

In the northern hemisphere 60°.8 or 69°.8 of annual temperature corresponds to the same latitude in the northern hemisphere, according as we compare the American system of climates or the Mediterranean one;—the concave or the convex parts of the isothermal lines.

At Port Jackson, where the thermometer descends sometimes below the freezing point, the warmest month is 77°.4, and the coldest 56°.

8. We find here the summer of Marseilles and the winter of Cairo .

In Louisiana 2 [Formel] of Lat. nearer the Equator, the warmest month is 79°.7, and the coldest 46°.9.

In Van Diemen’s Land, corresponding nearly in latitude to Rome, the winters are more mild than at Naples; but the coldness of the summers is such, that the mean temperature of the month of February appears to be scarcely 64°.4, or 66°.2, whilst at Paris, under a latitude more distant from the Equator by 7°, the mean temperature of the month of August is also from 64°.4 to 66°.2′, and at Rome above 77°.

Under the parallel of 51° 25′ south, the mean temperature of the Malouine Isles is well ascertained to be 47°.3.

At the same Lat. N. we find the mean temperature in Europe from 50° to 51°.8, and in America scarcely from 35°.6 to 37°.

4. The warmest and the coldest months are at London 66°.2 and 35°.6; at the Malouine Isles 55°.8 and 37°.

4. At Quebec, the mean temperature of the water is 14°; at the Malouine Isles 39°.6, though those isles are 4° of Lat. farther from the Equator than Quebec.

These numerical ratios prove, that, to the parallels of 40° and 50°, the corresponding isothermal lines are almost equally distant from the Pole in the two hemispheres; and that, in considering only the system of transatlantic climates between 70° and 80° of W. Long., the mean temperatures of the year, under the corresponding geographical parallels, are even greater in the southern than in the northern hemisphere.

Latitude.

Mean Temp. † Natchez, 31° 28′, 64°.8 Cincinnati, 3906, 53.8.

Latitude.

Mean Temp.

Cairo, 30° 2′ 72°.3 Funchal, —— 32 37 68 5 Algiers, —— 36 48 70 0

In Van Diemen’s Land the thermometer descends in February, in the morning, to 45°.

5. The mean of mid-day is 60°.

8. At Paris it is in August 73°.4.

In Van Diemen’s Land, in February the mean of the maxima is 78°8.; of the minima 54°.

5. At Rome these means are 86° and 64°.

5.—D’Entrecasteaux, Voyage, tom. i. p. 205. and 542.

The division of the heat between the different parts of the year, gives a particular character to southern climates.

In the southern hemisphere on the isothermal lines of 46°.4 and 50°.0, we find summers which in our hemisphere belong only to the isothermal lines of 35°.6 and 40°.

The mean temperature is not precisely known beyond 51° of S. Lat. Navigators do not frequent those regions when the sun is in the northern signs, and it would be wrong to judge of the rigour of winter, from the low temperature of the summer.

The eternal snows which in 71° of N. Lat. support themselves at the height of 2296 feet above the sea, descend even into the plains, both in South Georgia and in Sandwich Land in 54° and 58° of S. Lat. But these phenomena, however striking they may appear, do not by any means prove that the isothermal line of 32° is 5° nearer the South Pole than the North Pole.

In the system of transatlantic climates, the limit of eternal snow is not at the same altitude as in Europe; and in order to compare the two hemispheres, we must take into account the difference of longitude.

Besides, an equal altitude of the snows, does not by any means indicate an equal mean temperature of the year.

This limit depends parcularly on the coldness of summer, and this again on the quick condensations of the vapour caused by the passage of the floating ice.

Near the poles the foggy state of the air diminishes in summer the effect of the solar irradiation, and in winter that of the radiation of the globe.

At the Straits of Magellan, MM. Churruca and Galeano have seen snow fall in 53° and 54° of S. Lat. in the middle of summer; and though the day was 18 hours long, the thermometer seldom rose above 42°.8 or 44°.6 and never above 51°.8.

It is the more surprising to find in the Island of Georgia snow on the banks of the ocean, because 2° 39′ nearer the Equator at the Malouine Isles, the mean temperature of the summers is 53°.1, or 9° greater than at the point in our hemisphere in 71° of Lat. where the limit of perpetual snow exists at 2296 feet of absolute elevation.

But we must recollect, 1st, That the Malouine Isles are near a continent which is heated in summer; 2d, That Georgia is covered with mountains, and is placed not only in a sea open to the north, but under the influence of the perennial ices of Sandwich Land; and, 3dly, That in Lapland, 20° of Lat. produce in certain local circumstances 10°.8 of difference in the temperatures of the summers.

Baron Von Buch’s Travels in Lapland, vol. ii. p. 393,—420.

The inequal temperature of the two hemispheres, which, as we have now proved, is less the effect of the eccentricity of the earth’s orbit, than of the unequal division of the continents, determines the limit between the N. E. and S. E. Trade Winds.

But as this limit is much more to the north of the Equator in the Atlantic Ocean, than in the South Sea, we may conclude that, in a region between 130° and 150° of W. Long. the difference of temperature between the two hemispheres, is less great than farther to the east in 20° or 50° of longitude.

It is indeed under this region in the Great Ocean, that, as far as the parallel of 60°, the two hemispheres are equally covered with water, and equally destitute of dry land, which, radiating the heat during summer, sends the warm air towards the poles.

The line which limits the N. E. and S. E. Trade Winds, approaches the Equator, whereas the temperature of the hemispheres is different; and if, without diminishing the cold of the southern atmosphere, we could increase the inflexion of the isothermal lines in the system of transatlantic climates, we should meet the S. E. winds in 20° and 50° of W. Long.

to the north, and in 130° and 150° of W. Long.

to the south of the Equator .

Prevost, Journ.

de Phys. tom. xxxviii. p. 369.—Irish Trans. vol. viii, p. 374.

Humboldt’s Relat. Histor. tom. i. p. 225, 237.

The low strata of the atmosphere which rest upon the aqueous surface of the globe, receive the influence of the temperature of the waters.

The sea radiates less absolute heat than continents; it cools the air upon the sea, by the effect of evaporation; it sends the particles of water cooled and heavier towards the bottom; and it is heated again, or cooled, by the currents directed from the Equator to the Poles, or by the mixture of the superior and inferior strata on the sides of banks.

It is from these causes combined, that, between the tropics, and perhaps as far as 30° of Lat., the mean temperatures of the air next the sea, are 3°.6 or 5°.4 lower than that of the continental air.

Under high latitudes, and in climates where the atmosphere is coolest in winter, much below the freezing point, the isothermal lines rise again towards the Poles, or become convex when the continents pass below the seas .

Id. p. 67, 230. 242.

With respect to the temperature of the ocean, we must distinguish between four very different phenomena.

1st, The temperature of the water at the surface corresponding to different latitudes, the ocean being considered at rest, and destitute of shallows and currents.

2d, The decrease of heat in the superimposed strata of water. 3d, The effect of billows on the temperature of the surface water. 4th, The temperature of currents, which impell with an acquired velocity, the waters of our zone across the immoveable waters of another zone.

The region of warmest waters no more coincides with the Equator, than the region in which the waters reach their maximum of saltness.

In passing from one hemisphere to another, we find the warmest waters between 5° 45′ of N. Lat., and 6° 15′ of S. Lat. Perrins found their temperature to be 82°.3; Quevedo 83°.5; Churruca 83°.7, and Rodman 83°.

8. I have found them in the South Sea to the east of the Galapagos Isles 84°.

7. The variations and the mean result do not extend beyond 1°.

3. It is very remarkable that in the parallel of warmest waters, the temperature of the surface of the sea is from 3°.6 to 5°.4 higher than that of the superincumbent air.

Does this difference arise from the motion of the cooled particles towards the bottom, or the absorption of light, which is not sufficiently compensated by the free emission of the radiant coloric.

As we advance from the Equator to the Torrid Zone, the influence of the seasons on the temperature of the surface of the sea becomes very sensible; but as a great mass of water follows very slowly the changes in the temperature of the air, the means of the months do not correspond at the same epochs in the ocean and in the air.

Besides, the extent of the variations is less in the water than in the atmosphere, because the increase or decrease in the heat of the sea takes place in a medium of variable temperature, so that the minimum and the maximum of the heat which the water reaches, are modified by the atmospherical temperature of the months which follow the coldest of the warmest months of the year.

It is from an analogous cause, that in springs which have a variable temperature, for example, near Upsal , the extent of the variations of temperature is only 19°.8, while the same extent in the air from the month of January to August, is 39°.6.

In the parallel of the Canary Islands, Baron Von Buch found the minimum of the temperature of the water to be 68°, and the maximum 74°.

8. The temperature of the air in the warmest of the coldest months, is, in that quarter, from 64°.4 to 75°.2.

In advancing towards the north, we find still greater differences of winter temperature between the surface of the sea and the superincumbent air.

The cooled particles of water descend till their temperature reaches 39°.2; and hence in 46° and 50° of Lat. in the part of the Atlantic which is near Europe, the maximum and minimum of heat are

Gilbert’s Annalen, 1812, p. 129.

In the water at its surface, 68°.0 and 41°.9

In the air from the mean of warmest and coldest months, 66.2 and 35.6

The excess in the mean temperature of the water over that of the air, attains its maximum beyond the polar circle, where the sea does not wholly freeze.

The atmosphere is cooled to such a degree in these seas, (from 63° to 70° of Lat., and 0° of Long.) that the mean temperature of several months of winter descend on the continents to 14° and 10°.4, and on the coasts to 23° and 21°.2, while the temperature of the surface of the sea is not below 32° or 30°.

2. If it is true, that even in those high latitudes the bottom of the sea contains strata of water which, at the maximum of their specific gravity, have 39°.2 or 41° of heat, we may suppose that the water at the bottom contributes to diminish the cooling at the surface.

These circumstances have a great influence on the mildness of countries in continents separated from the Pole by an extensive sea.

Hitherto we have attended to the distribution of heat on the surface of the globe at the level of the sea.

It only remains for us to consider the 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 principle of which, according, to Laplace and Leslie , is the property of the air to increase its capacity for heat by its rarefaction.

If the globe was not surrounded by a mixture of elastic and aëriform fluids, it would not be sensibly colder at the height of 8747 yards than at the level of the sea.

As each part of the globe radiates in every direction, the interior of a spherical envelope which would rest on the top of the highest mountains, would receive the same quantity of radiant 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 temperature will be insensible, since the radius of the spherical envelope will be to that of the earth as 1.001 to 1.

Essay on Heat and Moisture, p. 11.; and Geometry, p. 495.

Considering the earth as surrounded with an atmospherical fluid, it is obvious, that the air heated at its surface will ascend, dilate itself, and be cooled, either by dilatation, or, by a more free radiation across the other strata that are equally rarified.

These are the ascending and descending currents, which keep up the decreasing temperature of the atmosphere .

Essay on Heat and Moisture, p. 11.; and Geometry, p. 495.

The cold of mountains is the simultaneous effect, 1st, Of the greater or less vertical distance of the strata of air at the surface of the plains and of the ocean. 2d, Of the extinction of light, which diminishes with the density of the superincumbent strata of air; and, 3d, Of the emission of radiant heat, which is favoured by air very dry , very cold, and very clear.

The mean temperature of our present plains would be lowered, if the seas should experience a considerable diminution.

The plains of continents would then become plateaux, and the air which rested on them would be cooled by the circumjacent strata of air, which, at the same level, would receive but a small portion of the heat emitted from the dry bottom of the seas.

Humboldt on Refraction below 10°, Observ. Astron. tom. i. p. 126.

Wells on Dew, p. 50.

The following Table contains the results of observations which I have made near the Equator, on the Andes of Quito, and towards the northern extremity of the torrid zone, in the Cordilleras of Mexico.

These results are true means, given either by stationary observations made during several years, or by insulated observations.

In these last, we have taken into account the hour of the day,—the distance of the solstices,—the direction of the wind,—and the reflection from the plains.

Height above the Level of the Sea.

Cordilleras of the Andes.

From 10° of North Lat. to 10° of South Lat. Mountains of Mexico.

From 17° of North Lat. to 21° of North Lat. Mean Temp. of the Year.

Examples, which may serve as a Type.

Mean Temp.

of the Year.

Examples, which may serve as a Type.

0 Toises. 0 Feet.

(Comparative heights in Europe have been added for every 1000 metres.)

Fahr. 81°.5 78°.80 500 Toises.

3197 Feet.

Vesuvius 3870 feet.

71°.24 67°.64 1000 Toises.

6394 Feet.

Hospice of St Gothard, 6806 feet.

64°.4 64°.4 1500 Toises.

9591 Feet.

Canigou, 9118 feet.

57°.74 57°.2 2000 Toises.

12,789 Feet.

Peak of Teneriffe, 12,169 feet.

44°.6 45°.5 2500 Toises.

15,985 Feet.

Mont Blanc, 15,662 feet.

37°.7 33°.8

Cumana, 33 feet.

Temp. of day, 78°.8—86° ————night, 71.6—74.3 Maximum, 90.9 Minimum, 70.2 Mean, ‒ 81.9

Vera Cruz, 0 feet. Temp. of day, 80°.6—86° — —— night, 78.26—82.4 in summer, —— — night, 66.2—75.2 64.4—71.6 in winter, Mean Temp. 77.72

Caraccas, 2906 feet. Temp. of day, 64°.4—73°4 —— ——night, 60.8—62.6 Maximum, 78.3 Minimum, 54.5 Mean, ‒ 69.4 Guaduas, 3769 feet.

Temp. Mean, 67°.5

Xalapa, 4330 feet.

Temp. Mean in winter, 64°.76 ——— of day, 57°.2—59 Chilpantzingo, 4523 feet, on a plateau which radiates.

Mean Temp. ‒ 69°.08

Popayan, 5815 feet. Temp. of day, 66°.2—75°.2 —— — night, 62.6—64.4 Mean, ‒ 65.66 Santa Fé de Bogota, feet.

8721 Temp.

of day, 59°—64°.4 —— —— night, 50—53.6 Minimum, 36.5 Mean, ‒ 57.74

Valladolid de Mechoachan, 6396 feet. Mean Temp. 66°.2—68°.

Mexico, 7468 feet. Temp. of day, 60°.8—69°.8 —— — night, 55.4—59 Warmest months, 52.7—59 Coldest months, 32—44.6 Mean, 62°.6

Quito, 9538 feet. Temp. of day, 60°.08-66°.74 —— — night, 48.2--51.8 Maximum, 71.6 Minimum, 42.8 Mean, ‒ 57.92

Toluca, 8823 feet.

Temp. Mean, ‒ 59° At the Nevado de Toluca, 11,178 feet. Temp. of spring.

48°.2

Micuipampa, 11,867 feet. Temp. of day, 41°—48°.2 —— — night, 35.6—31.28 Les Paramos, 11,480 feet.

Mean Temp. in gen. 47°.12

At the Nevado de Toluca, 12,178 feet.

Temp. in Sept. at noon, 52°.7 At Coffre de Perote, 12,136 f.

In February, at 9h, 50°.36

At the Inferior Limit of Perpetual Snows, 15,774 feet. Temp. of day, 39°.2—46°.4 —— ——night, 28.4—21.2 Chimborazo, 19,286 feet.

In June, at 1 o’clock, I have seen the therm. at 29°.12.

At the Pic del Fraille, 15,157 feet.

I have seen the thermometer in September at 39°.74.

The means given by the Mexican observations are a little different from those given by the observations on the Cordilleras.

When the differences and the coincidences amount to about a degree of Fahrenheit, they may be regarded as purely accidental.

The length of the day is more unequal in the 20th degree of latitude, but the perpetual snows do not descend 656 feet lower than under the Equator.

As the Cordilleras of New Granada, Quito, and Peru, present a great number of points where stationary observations have been made, I shall collect here the mean temperatures which M.

Caldas and I have determined with some certainty, and which all belong to a zone bounded by the parallels of 10° N. and 10° S. Lat.

I have used the mean temperature and barometrical measurements published at Santa Fé de Bogota by MM. Caldas and Restrepo in the Semanario del N. R. de Granada, tom. i. p. 273.; tom. i. p. 93.—341.

Alt. in Feet.

Mean Temp.

Coasts of Cumana, 0 80°.6 82.4 Tomependa, Amazons R. 1279 78.44 Tocayma, ‒ ‒ 1581 81.5 Antioquia, ‒ ‒ 1666 77.00 Neiva, ‒ ‒ 1702 77.00 Caraccas, ‒ ‒ 2906 69.44 Caripe, ‒ ‒ 2959 65.3 Carthago, ‒ ‒ 3149 74.84 La Plata, ‒ ‒ 3437 74.66 Guaduas, ‒ ‒ 3772 67.46 La Meya, ‒ ‒ 4225 72.50 Medellin, ‒ ‒ 4858 68.9 Estrella, ‒ ‒ 5645 65.84 Popayan, ‒ ‒ 5815 65.66 Loxa, ‒ ‒ 6855 64.4 Almaguer, ‒ ‒ 7413 62.6 Pamplona, ‒ 8016 61.16 Alt. in Feet.

Mean Temp.

Alausi, ‒ ‒ 7970 59°.00 Pasto, ‒ ‒ 8308 58.28 Santa Rosa, ‒ 8459 57.74 Cuenca, ‒ ‒ 8633 60.08 Santa Fé de Bogota, 8721 57.74 Hambato, ‒ ‒ 8849 60.44 Caxamarca, ‒ 9381 60.80 Llactacunga, ‒ 9473 59.00 Riobamba Nuevo, 9482 61.16 Tunja, ‒ ‒ 9522 56.66 Quito, ‒ ‒ 9538 57.92 Malbasa, ‒ ‒ 9971 54.50 Plateau de los Pastos, 10099 54.50 Les Paramos, ‒ 11480 47.30 At the Inferior Limit of Perpetual tual Snow, 15744 34.88

These thirty-two points are not insulated points, as balloons would be if they were fixed in the atmosphere at a perpendicular height of 16,400 feet.

They are stations taken on the declivity of mountains, upon that part of the solid mass of the globe which, in the form of a wall, rises into the higher regions of the atmosphere.

These mountains, too, have at each height particular climates, modified by the radiation of the plateaus on which they stand,—upon the slope of the ground,—the nakedness of the soil,—the humidity of the forests,—and the currents which descend from the neighbouring summits.

Without knowing the localities themselves, the effect of disturbing causes will be readily seen, by comparing in the preceding Table the mean temperatures which correspond to the same elevations; and the discussion of these observations would prove, also, that the extent of the variations is much less than is generally believed.

If we examine thirty-two temperatures, upon the hypothesis that a degree of cooling corresponds to an altitude of 200 metres (656 feet), we shall deduce the temperature of the plains (from 30°.6 to 82°.4) twenty-six times from that of elevated places.

For the other six deductions, the temperatures differ only about 3°.6; and the errors of observation are here combined with the effects of localities.

The air which rests on the plains of the Andes mixes itself with the great mass of the free atmosphere, in which there prevails under the torrid zone a surprising stability of temperature.

However enormous be the mass of the Cordilleras, it acts but feebly on the strata of air which are unceasingly renewed.

On the other hand, if the plains are heated during the day, they radiate as much during the night; for it is principally on the plains elevated 8856 feet above the sea, that the sky is most clear and uniformly serene.

At Peru, for example, the magnificent plateau of Caxamarca, in which the wheat yields the eighteenth, and barley the sixtieth grain, has an extent of more than twelve square leagues: it is smooth like the bottom of a lake, and sheltered by a circular wall of mountains free from snow.

Its mean temperature is 60°.8, yet the wheat is often frozen during the night; and in a season where the thermometer fell before sunrise to 46°.4, I have seen it rise in the day to 77° in the shade.

In the vast plains of Bogota, which are 656 feet less elevated than that of Caxamarca, the mean temperature, as established by the fine observations of Mutis, is scarcely 57°.74.

In comparing towns situated on elevated plains with those which are placed on the declivity of mountains, I have found for the first an augmentation of temperature, which, on account of the nocturnal radiation, does not exceed from 2°.7 to 4°.14.

This augmentation is a little greater in the lower regions of the Andes, in those large valleys whose smooth bottoms reach the height of from 1312 to 1640 feet, principally in the valley of La Madaleine, between Neiva and Honda .

It is singular to find in the middle of mountains heats which equal those of the plains, and which are more insupportable, as the air of the valleys is almost never agitated by the winds.

If we compare, however, the mean temperatures of these same places with those of the strata of the true atmosphere, or on the declivity of mountains, we shall find them only from 3°.6 to 5°.4.

On these grounds, we may place some confidence on the four results which we have deduced from such a great number of observations, for the perpendicular heights of 1000, 2000, 3000, and 4000 metres.

I have confined myself to a simple arithmetical mean, and to the fortuitous compensation of irregularities; for I could not have avoided employing an hypothesis on the decrease of heat, if I had wished to reduce to a standard height those heights which approach it the most.

I have added the observations with which an intimate knowledge of localities has furnished me.

1. For 1000 Metres (3280 feet) of Elevation.

Alt. in Feet.

Temp. Fahr.

Convent of Caripe, (thick and damp forests), ‒ 2959 65°.3 Caraccas, (a foggy sky, valley of small extent,) ‒ 2906 69.44 La Plata, (very warm, valley communicating with that of L’Alto Magdalena,) ‒ ‒ ‒ ‒ 3437 74.66 Carthago, (very warm valley of Cauca), ‒ ‒ 3149 74.84 2. For 2000 Metres (6560 feet) of Elevation.

Loxa, (a plateau of small extent), ‒ ‒ 6855 64.4 Almaguer, declivity covered with very thick vegetation), ‒ 7413 62.6 Popayan, (small plateau, a little elevated above the valley of Cauca,) ‒ ‒ ‒ ‒ ‒ 5815 65.66 3. For 3000 Metres (9840 feet) of Elevation.

Caxamarca, (very extensive plateau, sky serene,) ‒ 9381 60.80 Quito, (at the foot of Pinchincha, a narrow valley,) ‒ 9538 57.92 Tunja, (mountains of New Grenada), ‒ ‒ 9522 56.66 Malvasa, (elevated plains, cooled by the snows of the volcano of Puracé,) ‒ ‒ ‒ ‒ 9971 54.50 Los Pastos, (very cold plateau, from which rise snow covered summits,) ‒ ‒ ‒ ‒ ‒ 10099 54.50 Llactacunga, (temperate valley), ‒ ‒ 9473 59.0 Riobamba Nuevo, (arid plains of Tupia, covered with pumice-stone,) 9482 61.16

Between the tropics, the Cordilleras form the centre of the civilization and industry of Spanish America.

They are inhabited to the height of 4000 metres, (13,120 feet); and a small number of observations made on the back of the Andes, gives a sufficiently accurate idea of the mean temperature of the year.

In Europe, on the contrary, in the temperate zone, the high mountains are in general little inhabited.

The descent of the isothermal line of 32°, causes to cease the cultivation of crops of grain, at the point where they begin in the Cordilleras.

Stationary habitations are rare above 2000 metres (6560 feet) of elevation; and in order to judge with any precision of the mean temperature of the superincumbent beds of air, we must unite at least 730 thermometrical observations made in the course of a year .

Elevations of 400 metres (1312 feet) appear to have a very sensible influence on the mean temperature, even when great portions of countries rise progressively.

In order to establish this point, I have examined the temperatures of places situated almost on the level of the sea, and under the same parallels.

Whence, in the longitudes of Paris and Buda, and between the latitudes of 47° and 48°, and almost at the level of the sea, the mean temperature is from 50°.9 to 51°.44.

Under the same longitudes, we have,— By taking the means of these results, we cannot mistake the influence of small elevations, or of very extensive plateaus, on the decrease of the mean temperature.

Lat. Elevation in Feet.

Mean Temp.

Buda, ‒ ‒ ‒ 47°.29 512 51°.08 Paris, ‒ ‒ ‒ 48.50 116 51.08 Vienna, ‒ ‒ ‒ 48.12 551 50.54 Manheim, ‒ ‒ 49.20 384 50.18

Elevation in Feet.

Mean Temp.

Geneva, ‒ ‒ ‒ 1177 49°.28 Zurich, ‒ ‒ ‒ 1437 47.84 Munich, ‒ ‒ ‒ 1711 50.74 Berne, ‒ ‒ ‒ 1755 49.28 Marschling, ‒ ‒ 1834 51.98 Coire, ‒ ‒ ‒ 1991 48.92

Heated by the winds of Italy.

In spite of the winds of Italy.

Places situated between 46°—47° of North Lat. Elevations.

Mean Temperatures.

Metres.

Feet.

Of the Year.

Of the Coldest Months.

Of the Warmest Months.

Level of the sea, ‒ 0 53°.60 36°.32 69°.80 Geneva, ‒ ‒ 359 1177 49.64 34.16 66.56 Tegernsee , ‒ ‒ 744 2440 42.44 22.10 59.36 Peissenberg, ‒ 995 3264 41.00 20.84 57.02 Chamouni, ‒ ‒ 1028 3372 39.20 55.40 Hospice de St Gothard, 2076 6809 30.38 15.08 46.22 Col de Géant, ‒ 3436 11270 21.20 36.50

In comparing the mean temperature of superincumbent beds of air, I find that the isothermal line of 41°, which, in the parallel of 45°, is found at the height of 1000 metres, (3280 feet), makes the equatorial mountains of an absolute elevation of 4250 metres, (13,940 feet).

It had, however, been long believed, after Bouguer, that the inferior limits of perpetual snows characterised every where a bed of air, whose mean temperature was 32°; but I have shewn in a Memoir read to the Institute in 1808 , that this supposition is contrary to experience.

By uniting good observations, I have found, that at the limit of perpetual snows, the mean temperature of the air is,—

Observations Astronomiques, tom. i. p. 136.

Metres.

Feet. Mean Temp. of Limit of Perpetual Snows.

At the Equator, 4800 15,744 34°.70 In Temperate Zone, 2700 8,856 25.34 In Frigid Zone, in Lat. 68°—69°, 1050 3,444 21.20

As the heat of the higher regions of the atmosphere depends on the radiation of the plains, we may conceive, that, under the same geographical parallels, we cannot find, in the transatlantic climates, (on the declivities of rocky mountains), the isothermal lines at the same height above the level of the sea as in European climates.

The inflexions which these lines experience, when traced on the surface of the globe, necessarily influence their position in a vertical plane, whether we unite in the atmosphere points placed under the same meridians, or consider only those that have the same latitude.

Hitherto we have attempted to determine the mean temperatures which correspond under the Equator and in Lat. 45º and 47° to beds of the atmosphere equally elevated.

This determination is founded on stationary observations, and indicates the mean state of the atmosphere.

General physics has its numerical elements, as well as the system of the world; and these elements, so important in the theory of barometrical measurements and in that of refractions, will be perfected in proportion as natural philosophers shall direct their attention to the study of general laws.

Height, in Equatorial Zone, from 0°——10°.

Temperate Zone, from 45°——47°. Metres.

Feet. Mean Temp. Diff. Mean Temp. Diff. 0 0 81°.50 10°.26 53°.60 12°.60 974 3195 71.24 6.12 41.00 9.36 1949 6393 65.12 7.38 31.64 8.28 2923 9587 57.74 13.14 23.36 3900 12792 44.60 9.90 4872 15965 34.70

This Table proves, in conformity with the deductions of theory, that in the mean state of the atmosphere, the heat does not decrease uniformly in an arithmetical progression.

In the Cordilleras, (and the fact is extremely curious), we observe the decrease getting less and less between 1000 and 3000 metres, particularly between 1000 and 2500 metres of elevation, and then increasing anew from 3000 to 4000 metres.

The strata, where the decrease attains its maximum and its minimum, are in the ratio of 1 to 2. From the height of the Caraccas to that of Popayan and Loxa, 1000 metres produce a difference of 6°.3.

From Quito to the height of Paramos, the same 1000 metres change the mean temperature more than 12°.

6. Do these phenomena depend only on the configuration of the Andes, or are they the effect of the accumulation of clouds in the aërial ocean?

In considering that the Andes form an enormous mass, 3600 metres (11,808 feet) high, from which rise peaks or domes insulated and covered with snow, we may conceive how, from the point where the mass of the chain diminishes so rapidly, the heat decreases also with rapidity.

It is not easy, however, to explain, by an analogous cause, why the progressive cooling diminishes between 1000 and 2000 metres.

The great plateaus of the Cordilleras commence only at the height of 2600 or 2900 metres, (8528 or 9512 feet); and I am of opinion, that the slowness with which the heat decreases in the stratum of air between 1000 and 2000, is the triple effect of the extinction of light, or the absorption of the rays in the clouds,—of the formation of rain,—and the obstacle which the clouds oppose to the free passage of radiant heat.

The bed of air of which we speak, is the region in which are suspended the large clouds which the inhabitants of the plains see above their heads.

The decrease of temperature, which is very rapid from the plains to the region of clouds, becomes less rapid in that region; and if this change is less sensible in the temperate zone, it is no doubt because at the same height, the effect of radiation there is less sensible than above the burning plains of the equinoctial zone.

In these zones, too, the cooling appears to follow the same law in the beds of air of equal temperature; but the force of radiation varies with the temperature of the radiating beds.

The results which we have now discussed, deserve the preference over those which are deduced from observations made during excursions to the tops of some lofty mountains.

The first give for the

Metres. Cent. Fahr.

Metres.

Equinoctial Zone, 0—4900 1° or 1°.8 for 187

This is the mean result or the measure of the distribution of heat in the whole column of air.

The partial results are from the back of the Andes.

In these numbers, we recognise, as in the above Table, the influence of the region of clouds upon the decrease of heat.

In order to shew the utility of these numerical ratios, I shall give here the approximate calculation of the height of the plain of Thibet, deduced from the mean temperature of the month of October, which, according to the former, is 42°.26.

As the latitude of Tissoolumbo 29°, gives 69°.8 for the mean temperature of the plain; and as at Mount St Gothard, the mean temperature of October is even a little below that of the whole year, it is probable that the height of the plain of Great Thibet exceeds from 2900 to 3000 metres.— See my Memoir on the Mountains of India in the Ann. de Chim. et de Phys. 1817.

Note by the Editor.

As the cold meridian of the globe passes through the plains of Great Thibet, we conceive that the mean temperature of Lat. 29° in that plain, when reduced to the level of the sea, will be about 65°, and therefore that the height of the plain of Great Thibet will not exceed 2800 metres or 9184 feet.—D. B.

Heights in Metres.

Cent. Fahr. Metres.

0—1000 1° or 1°.8 for 170 1000—2000 1 or 1.8 for 294 2000—3000 1 or 1.8 for 232 3000—4000 1 or 1.8 for 131 4000—5000 1 or 1.8 for 180

Temperate Zone, 0—2900 1° or 1°.8 for 174

The last give for the

Cent. Fahr.

Metres.

Equinoctial zone, ‒ 1° or 1°.8 190 Parallels of 45°—47°, ‒ 1° or 1°.8 160—172

Saussure gives for the summer 160 metres, (525 feet); for winter 230, (754 feet); and for the whole year 195, (640 feet). M.

Ramond gives 165, (538 feet). M. D’Aubuisson 173 metres, (567 feet).—See Journ.

de Phys. tom. lxxi. p. 37.; De la Formul. Barometr. p. 189.; and my Recueil d’Obs. Astron. tom. i. p. 129.

This agreement is no doubt very remarkable, and the more so, as, in comparing stationary with insulated observations, we confound the mean state of the atmosphere in the course of a whole year with the decrease which corresponds to a particular season, or a particular hour of the day. M. Gay-Lussac found, in his celebrated aëronautical voyage from 0 to 7000 metres, (0 to 22,960 feet), a centigrade degree for 187 metres, near Paris, at a period when the heat of the plains was nearly equal to that of the equinoctial region.

It is on account of this observed equality in the decrease of heat, in reckoning from the standard temperature of the plains, that the astronomical refractions corresponding to angles below 10°, have been found the same under the equator and in temperate climates.

This result, contrary to the theory of Bouguer, is confirmed by observations which I have made in South America, and by those of Maskelyne at Barbadoes, calculated by M. Oltmanns.

We have seen, that between the tropics, on the back of the Cordilleras, we find, at 2000 metres of elevation, I will not say the climate, but the mean temperature of Calabria and of Sicily.

In our temperate zone, in 46° of Lat. we meet at the same elevation with the mean temperature of Lapland . This comparison leads us to an exact knowledge of the numerical ratios between the elevations and the latitudes, ratios which we find indicated with little precision in works on physical geography.

As the temperature varies very little in the course of a whole year in the equinoctial zone, we may form a pretty correct idea of the climate of the Cordilleras, by comparing them to the temperature of certain months in France or in Italy.

We find in the plains of Orinoco the month of August of Rome; at Popayan, (2988 feet), the month of August of Paris; at Quito (4894 feet), the month of May; in the Paramos, (5904 feet), the month of March at Paris.

The following are the results which I have obtained from exact data in the temperate zone, from the plains to 1000 metres of elevation.

Every hundred metres of perpendicular height, diminishes the mean temperature of the year, by the same quantity that a change of 1° of latitude does in advancing towards the Pole.

If we compare only the mean temperature of summer, the first 1000 metres are equivalent to 0°.81 Fahr.

From 40° to 50° of latitude, the mean heat of the plains in Europe decreases in Europe 12°.6 of Fahr.; and this same decrease of temperature takes place on the declivity of the Swiss Alps from 0 to 1000 metres of elevation.

Differences of Latitude, Compared with Differences of Elevation.

Mean Heat of the Year.

Mean Heat of Summer.

Mean Heat of Autumn. I. At the Level of the Sea. a. Latitude, 40°, ‒ 63°.14 77°.00 62°.60 b. Latitude, 50°, ‒ 50.54 64.40 II.

On the Declivity of Mountains. a. At the foot in 46° of Lat. 53.60 68.00 51.80 b. At an elevation of 1000 metres, 41.00 58.46 42.80

These numerical ratios are deduced from observations made on the temperature of the air.

We cannot measure the quantity of heat produced by the solar rays on the parenchyma of plants, or in the interior of fruits which receive their colour in ripening.

The fine experiment of MM.

Gay-Lussac and Thenard, the combustion of chlorine and hydrogen, proves what a powerful action direct light exercises on the molecules of bodies. But as the extinction of light is less upon the mountains in dry and rarified air, maize, fruit-trees, and the vine, still flourish at heights which, according to our thermometrical observations made in the air, and far from the ground, we ought to suppose too cold for the cultivation of plants useful to man. M. De Candolle, indeed, to whom the geography of vegetables owes so many valuable observations, has seen the vine cultivated in the south of France at 800 metres (2624 feet) of absolute height, when, under the same meridian, this same cultivation went on with difficulty at 4º of latitude farther north; so that if we consider only the ratios in France, an elevation of 100 metres, (328 feet), appears to correspond, not to 1°, but to half a degree of latitude .

See my Prolegomena de Distributione Plantarum, p. 151. 163. The small differences between the numbers given in the Prolegomena and in this Memoir, written subsequently, should be ascribed to the constant desire which I have had to perfect the mean results.

(To be concluded in next Number.)

On Isothermal Lines, and the Distribution of Heat over the Globe.

By Baron Alexander de Humboldt.

(Concluded from Vol. IV. p. 281.)

I SHALL now conclude this Memoir by the enumeratıon of the most important results which have been obtained by Baron Von Buch, M. Wahlenberg, and myself, on the distribution of heat in the interior of the earth, from the Equator to 70° of N. Lat., and from the plains to 3600 metres (11,808 feet) of elevation.

I shall limit myself to an enumeration of the facts.

The theory by which these facts are connected, will be found in the fine analytical work with which M. Fourier will soon enrich natural philosophy.

The interior temperature of the earth is measured either by the temperature of subterraneous excavations, or by that of springs.

This kind of observation is very liable to error, if the traveller does not pay the most minute attention to local circumstances, which are capable of altering the results . The air, when cooled, accumulates in caverns, which communicate with the atmosphere by perpendicular openings.

The humidity of rocks depresses the temperature by the effect of evaporation.

Caverns that have little depth are more or less warmed, according to the colour, the density, and the moisture, of the strata of stone in which nature has hollowed them.

Springs indicate too low a temperature, if they descend rapidly from a considerable height upon inclined strata.

There are some under the torrid zone and in our climate, which do not vary in their temperature throughout the whole year more than half a degree; and there are others which shew the mean temperature of the earth only by observing them every month, and taking the mean of all the observations.

From the Polar circle to the Equator, and from the tops of mountains towards the plains, the progressive increase of the temperature of springs diminishes with the mean temperature of the ambient air.

The temperature of the interior of the earth is, at

Baron von Buch, in the Bibl. Brit. tom. xix. p. 263.; Saussure, Voyages, sect. 1418.; Wahlenberg, De Veget. Helvet. Pl. 77.—84.; Gilbert, Annalen, 1812, p. 150. 160. 277.; Lambert, Pyrometrie, p. 296.

Dr Roebuck appears to have been the first who entertained exact notions on the temperature of springs, and upon their relation to the mean temperature of the air; Phil. Trans. 1775, vol. lxv. p. 461.

Lat. Temp. Fahr. Lat. Temp. Fahr.

Vadso, 70°.0 35°.96 Paris, 48° 50′ 53.

°6 Berlin, 52.31 49.28 Cairo, 30 2 72.5

In equinoctial America, I have found it in the plains from 77° to 78°.8.

The following are examples of the decrease of temperature from the plains to the tops of mountains.

Alt. in Feet.

Temp. Fahr.

Spring of Utliberg, near Zurich, ‒ 1532 48°.92 Ditto of Rossbaden at St Gothard, ‒ 7016 38.30

Between the Tropics I have found,

Alt. in Feet.

Temp. Fahr.

Springs of Cumanacoa, ‒ ‒ 1,148 72°.5 Ditto Montserrate, above Santa Fé de Bogota, 10,680 59.9 Ditto in the Mine of Hualgayoc in Peru, 11,759 53.24

In the plains, and to the height of 3280 feet, between the parallels of from 40° to 45°, the mean temperature of the earth is nearly equal to that of the ambient air; but very accurate observations by Baron Von Buch and Wahlenberg tend to prove, that in high latitudes, towards the top of the Swiss Alps, for example, beyond the height of 1400 or 1500 metres (4592 or 4920 feet), the springs and the earth are 5°.4 warmer than the air.

Zone of 30°—55°. Lat. Mean Temp. of Air, Fahr. Temp. of the Interior of the Earth.

Cairo, ‒ ‒ 30° 2′ 72°.68 72°.50 Natchez, ‒ ‒ 31 28 64.76 64.94 Charlestown, ‒ ‒ 33 0 63.14 63.50 Philadelphia, ‒ ‒ 39 56 53.42 52.16 Geneva, ‒ ‒ ‒ 46 12 49.28 50.74 Dublin, ‒ ‒ ‒ 53 21 49.10 49.28 Berlin, ‒ ‒ ‒ 52 31 47.30 49.28 Kendal, ‒ ‒ 54 17 46.22 47.84 Keswick, ‒ ‒ 54 33 48.02 48.56 Zone of 55°—70°.

Carlscrona, ‒ ‒ 56 6 46.04 47.30 Upsal, ‒ ‒ 59 51 41.90 43.70 Umeo, ‒ ‒ 63 50 33.26 37.22 Vadso, ‒ ‒ 70 0 29.66 35.96

At Enontekies, in 68 [Formel] ° of Lat. the difference between the mean temperatures of the earth and the air, is so great as 7°.74.

Analogous differences are observed on the back of the Alps, at the altitude of 1400 metres (4592 feet).

In the following small table, I have added the mean temperature of the atmosphere, by supposing, with M. Ramond, that there is a decrease of 1° centigrade for 164 metres (1° Fahr.

for 300 feet nearly), and by placing the temperature of 32° (according to observations made at the Hospice of St Gothard), at 1950 metres (6396 feet) of elevation.

Alt. in Feet.

Temperature. Springs. Air. Rigi Kaltebad, ‒ 4717 43°.7 38°.12 Pilate, ‒ ‒ 4858 41.0 37.40 Blancke Alp, ‒ 5786 37.4 35.78 Rossbaden, ‒ ‒ 7016 38.3 31.38

It may be objected, that in the Alps of Switzerland, the temperature of springs has only been observed from the beginning of June to the end of September, and that the differences between the air and the interior of the earth would almost entirely disappear, if we knew the temperature of the springs during the whole year.

It must not be forgotten, however, that the springs of the Alps did not vary in the space of four months at the time of the observations of M. Wahlenberg;—that among the small number of scanty springs which indicate changes of temperature in different seasons, these variations amount from June to September to 11° or 15°;—and that several springs, particularly those which are very copious, do not vary during a whole year more than half a degree of Fahrenheit.

It appears to me, therefore, sufficiently certain, that where the earth is covered with a thick stratum of snow, while the temperature of the air descends to 15° or — 4° of Fahrenheit, the temperature of the earth is above the mean temperature of the air.

When we consider what a large portion of the globe is covered with the sea, and examine the temperature of the deepest waters , we are constrained to admit, that in islands, along coasts, and perhaps even in continents of small extent, the interior heat of the earth is modified by the proximity of the strata of rocks on which the waters of the ocean rest.

At Funchal in Madeira, the temperature of caverns appears to be 61°.16, and consequently 7°.2 below that of the air.—Phil. Trans. 1778, p. 372.

I have considered successively in this memoir, the distribution of heat,

1. At the surface of the globe.

2. On the declivity of mountains.

3.

In the ocean.

4. In the interior of the earth.

In explaining the theory of isothermal lines and their inflexions, which determine the different systems of climates, I have endeavoured to reduce the phenomena of temperature to empirical laws.

These laws will appear much more simple, when we shall have multiplied and rectified by degrees the numerical elements which are the results of observation.

In the following general Table of the distribution of heat, the temperatures are expressed in degrees of Fahrenheit; the longitudes are reckoned from east to west of the meridian of the observatory of Greenwich.

The mean temperatures of the seasons have been calculated, so that those of the months of December, January, and February, form the mean temperature of Winter.

An asterisk (*) is prefixed to those places whose mean temperatures have been most accurately determined, and in general by means of 8000 observations.

The isothermal lines have a convex summit in Europe, and two concave summits in Asia and Eastern America

Isothermal Bands.

Names of Places.

Position.

Mean Temp.

of the Year.

Distribution of Heat in the different Seasons.

Maximum and Minimum. Lat. Long.

Height in Feet.

Mean Temp.

of Winter.

Mean Temp.

of Spring.

Mean Temp.

of Summer.

Mean Temp.

of Autumn.

Mean Temp.

of Warmest Month.

Mean Temp.

of Coldest Month.

Isothermal Bands from 32° to 41°. Nain, ‒ 57° 8′ 61°20′ W 0 26°.42 — 0°.60 23°.90 48°.38 33°.44 51°.80 —11°.20 1 * Enontekies, 68 30 20 47 E 1356 26.96 + 0.68 24.98 54.86 27.32 59.54 — 0.58 2 Hospice de St Gothard, 46 30 8 23 E 6390 30.38 18.32 26.42 44.96 31.82 46.22 15.08 3 North Cape, 71 0 25 50 E 0 32.0 23.72 29.66 43.34 32.08 46.58 22.10 4 * Uleo, ‒ 65 3 25 26 E 0 35.08 11.84 27.14 57.74 35.96 61.52 7.70 5 * Umeo, ‒ 63 50 20 16 E 0 33.26 12.92 33.80 54.86 33.44 62.60 11.48 6 * St Petersburg, 59 56 30 19 E 0 38.84 17.06 38.12 62.06 38.66 65.66 8.60 7 Drontheim, 63 24 10 22 E 0 39.92 23.72 35.24 61.24 40.10 64.94 19.58 8 Moscow, ‒ 55 45 37 32 E 970 40.10 10.78 44.06 67.10 38.30 70.52 6.08 9 Abo, ‒ 60 27 22 18 E 0 40.28 20.84 38.30 61.88 40.64 — — 10 Isothermal Bands from 41° to 50°.

* Upsal, ‒ 59 51 17 38 E 0 42.08 24.98 39.38 60.26 42.80 62.42 22.46 11 * Stockholm, ‒ 59 20 18 3 E 0 42.26 25.52 38.30 61.88 43.16 64.04 22.82 12 Quebec, ‒ 46 47 71 10 W 0 41.74 14.18 38.84 68.00 46.04 73.40 13.81 13 Christiania, ‒ 59 55 10 48 E 0 42.8 28.78 39.02 62.60 41.18 66.74 28.41 14 * Convent of Peyssenburg, 47 47 10 34 E 3066 42.98 28.58 42.08 58.46 42.98 59.36 30.20 15 * Copenhagen, 55 41 12 35 E 0 45.68 30.74 41.18 62.60 48.38 65.66 27.14 16 * Kendal, ‒ 54 17 2 46 W 0 46.22 30.86 45.14 56.84 46.22 58.10 34.88 17 Malouin Islands, 51 25 59 59 W 0 46.94 39.56 46.58 53.06 48.46 55.76 37.40 18 * Prague, ‒ 50 5 14 24 E 0 49.46 31.46 47.66 68.90 50.18 — — 19 Gottingen, ‒ 51 32 9 53 E 456 46.94 30.38 44.24 64.76 48.74 66.38 29.66 20 * Zurich, ‒ 47 22 8 32 E 1350 47.84 29.66 48.20 64.04 48.92 65.66 26.78 21 * Edinburgh, ‒ 55 57 3 10 W 0 47.84 38.66 46.40 58.28 48.56 59.36 38.30 22 Warsaw, ‒ 52 14 21 2 E 0 48.56 28.76 47.48 69.08 49.46 70.34 27.14 23 * Coire, ‒ 46 50 9 30 E 1876 48.92 32.36 50.00 63.32 50.36 64.58 29.48 24 Dublin, ‒ 53 21 6 19 W 0 * 49.10 39.20 47.30 59.54 50.00 61.16 35.42 25 Berne, ‒ 46 5 7 26 E 1650 49.28 32.00 48.92 66.56 49.82 67.28 30.56 26 * Geneva, ‒ 4612 6 8 E 1080 49.28 34.70 47.66 64.94 50.00 66.56 34.16 27 * Manheim, ‒ 49.29 8 28 E 432 50.18 38.80 49.64 67.10 49.82 68.72 33.44 28 Vienna, ‒ 48 12 16 22 E 420 50.54 32.72 51.26 69.26 50.54 70.52 26.60 29 Isothermal Bands from 50° to 59°.

* Clermont, ‒ 4546 3 5 E 1260 50.00 34.52 50.54 64.40 51.26 66.20 28.04 30 * Buda, ‒ 47 29 19 1 E 494 51.08 33.98 51.08 70.52 52.34 71.60 27.78 31 Cambridge, (U.S.) 42 25 71 3 W 0 50.36 33.98 47.66 70.70 49.82 72.86 29.84 32 * Paris, ‒ 48 50 2 20 E 222 51.08 38.66 49.28 64.58 51.44 65.30 36.14 33 * London, ‒ 5130 0 5 W 0 50.36 39.56 48.56 63.14 50.18 64.40 37.76 34 Dunkirk, ‒ 51 2 2 22 E 0 50.54 38.48 48.56 64.04 50.90 64.76 37.75 35 Amsterdam, 52 22 4 50 E 0 51.62 36.86 51.62 65.84 51.62 66.92 35.42 36 Brussels, ‒ 50 50 4 22 E 0 51.80 36.68 53.24 66.20 51.08 67.28 35.60 37 * Franeker, ‒ 52 36 6 22 E 0 51.80 36.68 51.08 67.28 54.32 69.08 32.90 38 Philadelphia, 39 56 75 16 W 0 53.42 32.18 51.44 73.94 56.48 77.00 32.72 39 New York, 40 40 73 58 W 0 53.78 29.84 51.26 79.16 54.50 80.78 25.34 40 * Cincinnati, ‒ 39 6 82 40 W 510 53.78 32.90 54.14 72.86 54.86 74.30 30.20 41 St Malo, ‒ 4839 2 1 W 0 54.14 42.26 52.16 66.02 55.76 66.92 41.74 42 Nantes, ‒ 47 13 1 32 W 0 54.68 40.46 54.50 68.54 55.58 70.52 39.02 43 Pekin, ‒ 39 54 116 27 E 0 54.86 26.42 56.30 82.58 54.32 84.38 24.62 44 * Milan, ‒ 45 28 9 11 E 390 55.76 36.32 56.12 73.04 56.84 74.66 36.14 45 Bourdeaux, ‒ 44 50 0 34 W 0 56.48 42.08 56.48 70.88 56.30 73.04 41.00 46 Isothermal Band from 59° to 63°.

Marseilles, ‒ 43 17 5 22 E 0 59.00 45.50 57.56 72.50 60.08 74.66 44.42 47 Montpellier, 43 36 3 52 E 0 59.36 44.06 56.66 75.74 60.98 78.08 42.08 48 * Rome, ‒ 41 53 12 27 E 0 60.44 45.86 57.74 75.20 62.78 77.00 42.26 49 Toulon, ‒ 43 7 5 50 E 0 62.06 48.38 60.80 75.02 64.40 77.00 46.40 50 Nangasacki, 32 45 129 55 E 0 60.80 39.38 57.56 82.94 64.22 86.90 37.40 51 * Natchez, ‒ 31 28 90 30 W 180 64.76 48.56 65.48 79.16 66.02 79.70 46.94 52 Isothermal Band from 68° to 77°.

* Funchal, ‒ 32 37 16 56 W 0 68.54 64.40 65.84 72.50 72.32 75.56 64.04 53 Algiers, ‒ 3648 3 1 E 0 69.98 61.52 65.66 80.24 72.50 82.76 60.08 54 Isothermal Bands above 77°.

* Cairo, ‒ 30 2 31 18 E 0 72.32 58.46 73.58 85.10 71.42 85.82 56.12 55 * Veracruz, ‒ 19 11 96 1 W 0 77.72 71.96 77.90 81.50 78.62 81.86 71.06 56 * Havannah, ‒ 23 10 82 13 W 0 78.08 71.24 78.98 83.30 78.98 83.84 69.98 57 * Cumana, ‒ 10 27 65 15 W 0 81.86 80.24 83.66 82.04 80.24 84.38 79.16 58

1 Coast of Labrador.

Two years of observations.

Floating ice towards the east.

A transatlantic climate.

Mean temp. of Oct. about 32°.72; Nov. 26°.68.

2 Centre of Lapland.

A European climate.

Fine vegetation.

June, 49°.46; July, 59°.54; Aug. 55°.94; Sept. 41°.74; Oct. 27°5; Nov. 12°.38. Inland situation.

Specimen of a continental climate.

3 Eleven years of observations, calculated afresh in decads by Wahlenberg.

Thermometer verified by Saussure.

Mean temp. of seven months of the year below 32°.

Winds blow from Italy in the winter.

Minimum observed in the winter— 0°.4; in Aug. at noon, in the shade, maximum 54°.5; the nights in Aug. frequently from 33°.8 to 29°.3; the mean temp. of Oct. 31°.1 represents that of the whole year; at the Col de Géant, 10,598 feet high, the mean temp. of July is 36°.

5. We find 32° to be the mean temp. in Europe in 45° of latitude, at 5,400 feet high; at the parallel of the Canaries, at 12,300 feet; in the Andes, under the Equator, at 16,500 feet.

4 Buch, Voy.

en Norw. ii. 416. Specimen of the climate of the islands and coasts in the north of Europe.

April, 30°.02; May, 33°.98; Oct. 32°; Nov. 25°.88.

At Alten, Lat. 70°, mean temp. of July, 63°.5; a continental climate.

5 Finland, eastern coast.

May, 40°.82; June, 55°.04; July, 61°.52; Aug. 56°.66; Sept. 46°.58; Oct. 38°.66; Nov. 24°.62.

Julin and Buch.

6 Eastern coast of Western Bothnia.

Dr Nœzen.

March, 23°.18; April, 33°.98; Oct. 38°.12; Nov. 24°.62.

7 Euler.

Mean temp. of the year, 37°.94. Inochodzow.

Acta. Petr. xii. 519,—533.

8 Two years.

Berlin, in the Mem. de l’Acad. de Drontheim, iv. 216. April, 34°.34; May, 50°.74; Oct. 39°.2; Nov. 27°.68.

Climate of the west coast of Europe.

9 Four years.

Journal de Phys. xxxix. 40. A continental climate.

Winter colder, and summer warmer than at Petersburg.

Eastern part of Europe; height as taken from Stritter.

(Chamouni, Lat. 46° 1′; Long.

6° 18′ E.; height, 3,168 feet; mean temp. 39°.

2.)

10 Twelve years.

Kirwan.

Cotte, mean of the year, 41°.18; of the summer, 67°.46; too high.

West coast of Finland.

11 Observations from 1774 to 1804, made by Mallet, Prosperin, Holmquist, and Schleling, calculated by M. De Buch, Voy.

de Norw. ii. 309. It is, perhaps, the place the mean temp of which is the best determined.

Winters more serene than at Stockholm; colder on account of the radiation of the ground and the air.

12 Thirty-nine years of observations, 15 of which are very good.

Wargentin.

Cotte, mean temp. of the year, 44°.24.

Five months below 32° as at Petersburg.

13 Four years.

A transatlantic climate.

14 Buch, two years.

Mean temp. of the winter often scarcely 31°.

1. West coast.

15 Alps of Bavaria.

Six years’ observations, calculated by M. Wahlenberg.

Many fruit trees.

Convent of Tegernsée, in Bavaria, height of, 2,292 feet; mean temp. of 1785, 42°.44; Peyssenberg, 41°.

16 Bugge.

Three months below 32°.

Under the Equator, mean temp. of 44°.6, at an elevation of 18,000 feet.

17 Dalton.

West of England.

Climate of islands; springs 47°.84.

Keswick, Lat. 54° 33′, Long.

3° 3′ W.; mean temp. 48°.02; springs, 48°.56.

18 Kirwan.

Scarcely two years’ observations.

Southern latitude.

19 Strnadt.

Fifteen years.

Climate of the continent of Europe.

20 Maier.

21 Six years’ observations of M. Escher, calculated by Wahlenberg.

The town is situated in a hollow, to which those warm winds cannot penetrate, that render the winters more temperate in the other parts of Switzerland.

22 The calculation has been made from six years of excellent observations, by Professor Playfair; during this time the thermometer was never seen above 75°.74 . Vegetation continues from March 20. to Oct. 20.; mean temp. of these seven months is from 55°.76 to 50°.90, according as the years are more or less fruitful; wheat does not ripen if the mean temp. descends to 47°.66.

See Edinburgh Transactions, vol. ix. p. 209.—Ed.

23 Guittard.

Only three years.

Mean temp. a little too high. Eastern part of Europe.

A continental climate.

24 Four years of observations, by M. de Salis Sewis, calculated by M. Wahlenberg.

Mountains of the Grisons.

25 Kirwan. Irish Trans. viii. 203. and 269. Specimen of the climate of the islands.

Coldest days, 23°; interior of the ground, 49°.28.

Hamilton.

26 The climate of Berne is a continental climate, in comparison with that of Geneva; there is no lake near it.

27 Seven years of observations.

Saussure.

Mean temp. 50°74. Voy.

§ 1418. I find the mean temp. from 1796—1815, 49°.7.

Interior of the earth, 51°.98.

Pictet, Bibliotheque Brit. 1817, iv. 109.

28 Six years.

29 Austria.

Berlin, Lat. 52° 31′; mean temp. probably 46°.4 to 47°.3; according to Beguelin, 48°.74; springs, 49°.28.

Ratisbon, Lat. 49°; height, 1,104 feet; mean temp. 47°.66.

Munich, Lat. 48° 8′; height, 1,608 feet; mean temp. 50°.74.

30 Ramond.

Seven years of excellent observations.

The mean of the months, at noon, well ascertained; winter, 39°.92; spring, 57°.02; summer, 70°.88; autumn, 57°.92. Mem. Inst. 1812, p. 49. Cotte, mean temp. 51°.26.

31 Wahlenberg, Flor.

Carp. p. 90. Continental climate.

Height of the observatory, 474 feet.

32 Two years, near Boston, in New England.

Transatlantic climate.

The thermometer sometimes descends to 0°.

33 Eleven years (1803—1813) of observations made at the observatory.

A greater number of years will, perhaps, give the mean temp. a little higher.

Vaults, 53°.06.

Kirwan finds for Paris, from seven years of observations of unequal value, 51°.62; he fixes upon 52°.

7. Cotte, from 29 years of observations, (Journ. de Phys. 1782, July), 53°.24. Cotte, for 33 years, (1763—1781, Mem. Instit. iv. 266.), 52°.34.

The extraordinary year of 1816 offers the mean temp. of 48°.74; winter, 37°.04; spring, 48°.92; summer, 59°.54; autumn, 50°:

the preceding year, 1815, offers a mean temp. of 50°.74; winter, 37°.04; spring, 52°.7; summer, 62°.78; autumn, 50°.74. Arago.

Mean temp. of Montmorency, for 33 years, 50°.74; height, 498 feet.

Cotte, Strasburg, Lat. 48° 34′; height, 480 feet; mean temp. 49°.28.

Herrenschneider.

34 Dr Young.

Mean temp. varies from 47°.84 to 51°.62, (Lectures, ii. 453.) Cavendish, (Trans. 1788, p. 61.), 48°.74, Roebuck, Hunter, and Kirwan, 51°.62.

Horsley, 51°.26.

According to Kirwan, the four seasons in London are, 39°.56, 50°.9, 64°.76, 51°.98; at Paris, 36°.68, 51°.08, 65°.84, 52°.52; from whıch results, London, 51°.62; Paris, 51°.44. Cotte (Journ. de Phys. xxxix. 36.) thinks London is 51°.26, and Paris, 52°.34.

The difference which we observe in cultivated plants depends less upon mean temp. than upon direct light, and the serenity of the atmosphere.

35 Seven years.

Cotte.

Lisle, 48°.38; Rouen, 51°.44; Cambray, 51°.98; Soissons, 53°.42; Rethel, 53°.24; Metz, 52°.88; Nancy, 51°.98; Etampes, 51°.08; L’Aigle, 50°.9; Brest, 54°.14; Mayenne, 51°.98.

36 Mohr, and Van Swinden.

Five years.

37 Thirteen years.

Temperature rather too high?

38 Eleven years.

Van Swinden.

From 1771—1783.

Mean temp. 51°.26.

39 Concave transatlantic summit.

Seven years of observations give 54°.86; for the four seasons, 33°.98, 53°.06, 75°.2, 56°.12.

Rush, 52°.52, (Drake’s View of Cincin. p. 116.)

Coxe, 54°.14. M.

Legaux finds for 17 years, for Springmill on the Schuylkill, Lat. 40° 50′; mean temp. 53°.42.

Springs, near Philadelphia, 54°.86, Warden.

40 Two years only.

Retif de la Serve.

The thermometer sometimes descends to — 4° in the parallel of Naples!

Springs, 54°.86.

Ipswich, Lat. 42° 38′; mean temp. 50°.

Williamsburg, in Virginia, 58°.

1. Cotte and Kirwan.

Transatlantic climates.

41 Transatlantic climates west of the Alleghanys.

Good observations, 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 the shade, without reflection; [Formel] of all the winds SW.; springs near Cincinnati, 54°.32.

Little snow falls; but it is abundant between Lat. 40° and 42°.

42 Three years only.

Bougourd.

Dijon, height, 810 feet; Lat. 47° 19′; mean temp. 50°.

9. Besançon, height, 804 feet; Lat. 47° 14′; mean temp. 51°.26.

43 Six years.

Duplessis, and Boudan.

Temperature of the summer too high?

Rochelle, 53°.06; Poitiers, 52°.7.

44 Amyot.

Six years.

Concave.

Asiatic summit.

Three months below 32°, as at Copenhagen; the summer like that at Naples.

45 One of the best determined points.

The years 1789—1812 are calculated in decads of days.

Observations of the Astronomer Reggio, April, 55°.76; Oct. 58°.

1. The two decads which approach the nearest to the mean temp. of the year, are, the first of April, 53°.24; and the last of Oct. 54°.68.

The mean temps.

for January have varied in 10 years from 24°.98 to 38°.48; those of July, from 71°.42 to 78°.44; the mean of the years, from 54°.5 to 57°.

2. (Reggio, taking only 24 maxima and minima in a year for 1763—1798; mean temp.

55.4, Ephem. Mil. 1779, p. 82.)

46 Ten years.

Guyot.

Lyons, 528 feet, 55°.76.

Mafra, near Lisbon, Lat. 38° 52′; height, 600 feet; mean temp. 56°.3, too small.

Mem. de Lisbonne, ii. 105—158.

47 Seven years, (1777—1782).

St Jacques de Sylvabelle.

The thermometer sometimes descends to 23°.

Cotte, Traité de Met. ii. 420.) 34 years (Raymond, in Mem. de la Soc. de Med. 1777, p. 86.) give 62°.06. Cotte (Journ. de Phys. xxxix. 21.) fixes it at 58°.64.

Kirwan, at 61°.24.

The observations made at the Royal Observatory of Marseilles can alone decide.

48 Ten years.

Nismes, 60°.26; Perpignan, 59°.54; Tarascon, 59°.9; Arles, 59°; Rieux, 57°.2: Montauban, 55°.58; Tonains, 54°.86; Dax, 54°.14; Rodez, 57°.02; Aix, 56°.66.

Under the equator, 57°.74, at 9,000 feet of elevation.

49 William Humboldt.

Calandrelli, 60°.08.

The thermometer sometimes descends to 24°.5, and rises to 99°.

5. Naples, 67°.1; Toaldo, probably 63°.5; Florence, 61°.52; Tartini, too high; Lucca, 60°.44; Genoa, 60°.26; Bologna, 56°.3; Verona, 55°.76; Venice, 56°.48; Padua, 56°.

3. Kirwan regards it as an established fact, that in Europe the mean temp. in Lat. 40°, is 61°.88; in Lat. 50°, 52°.52.

50 Only two years.

Barberet, and d’Angos.

Sheltered by mountains.

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 of 6000 feet.

52 West of the Alleghanys, in Louisiana.

Four years.

Dunbar.

Transatlantic climate.

53 Madeira.

Heberden.

Climate of islands.

St Croix, of Teneriffe, 71°.42.

The remainder of the island of Teneriffe, in the plains, 69°.26. Buch.

54 Old observations of Tartebout.

They appear good.

Bagdad, Lat. 33° 19′; according to Beauchamps, 73°.76.

The four seasons, 50°.74; 74°.64; 92°.66; 77°; but there was reflection from a house.

The thermometer falls to 29°.44.

Under the Equator, at 3,000 feet high; mean temp. 71°.24.

55 The calculations are made from the observations of Nouet, (Decade, ii. 213.)

The following are the mean temps.

of the 12 months:

58°.1; 56°.12; 64°.58; 77°.9; 78°.26; 83°.66; 85°.02; 85°.82; 79°.16; 72°.32; 62°.96; 61°.24. (Niebuhr, 72°.

2.) Temp.

of Joseph’s Well, 72°.5.

Catacombs of Thebes, 81°.

5. Well of the great pyramid, surrounded by sand, 88°.16. Jomard.

Bassora, on the Persian Gulf; mean temp. 77°.9; winter, 64°.04; summer, 90°.86; July, 93°.2.

56 Orta.

Humboldt, Nouv. Esp. iv. 516. Jamaica, coast, 80°.

6. Blagden.

57 Ferrer, 1810—1812.

Con. des Tems, 1817, p. 338. Wells of 10 feet deep; air, 75°.92; water, 74°.48; in 1812, maximum, Aug. 14. 86°; minimum, Feb. 20. 61°.52.

Grottos, 81°.

5. Humboldt, Observ. Astron. i. 134.

58 Humboldt.

Pondicherry, 85°.1; Madras, 80°.42; Manilla, 78°.08; Isle de France, coast, 80°.42.