Alexander von Humboldt.

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tain ranges rising within the region of perpetual snow. Causes of
vicinity to, or distance from the ocean, insular or inland
position, extensive natural irrigation, geological peculiari-
ties of soil and stratification, and the peculiar develop-
ment of vegetable life, all more or less influence the
temperature of regions, establishing temperate climes
alike within the torrid and the frigid zones, and filling the
ample beds of the Nile and the Euphrates, from the
snows that melt within the range of the equatorial sun.
It is now well known that the magnetic pole does not
coincide with the true geographical pole. The results of
Humboldt's isothermal system, as deduced from his own
personal investigation, has led to extended observations by
others, which also promise to be productive of the most
important results. One of these aims at establishing the Position of
actual position of the cold poles, or the precise points in lo^velt"
the northern and southern hemispheres, where the mean temperature,
temperature is lower than at any other part of the globe.
Already an approximation to this has been made, an<l
though it is still unsafe to attempt to deduce any abso-
lute or precise conclusions from this, it is remarkable that
the eastern and western poles of lowest mean tempera-
ture, appear very nearly to coincide with the magnetic
poles of the earth. This remarkable result is well calcu-
lated to excite the liveliest interest in men of science, and
to urge them to renewed zeal. It may, indeed, prove
that the connection of the cold and magnetic poles is
merely accidental, but meanwhile it seems more probable
that it points to some important, and hitherto imknown
law, which shall yet reveal the full nature and extent
of operation of that mysterious power which is known as
magnetism.

A glance at the map of the two hemispheres, accompa- Variations
nied with some knowledge of the ascertamed isothermal temperaturs
data, is sufficient to show how great are the variations of
mean temperature that may be looked for. The geogra-



408



VARIATIONS OF MEAN TEMPERATURE.



Isothermal
zones.



CHAPTER pliical equatorial line passes through the continents of
^ ^^ ^^' Africa and South America, leaving nearly a third of the

Kquatnrial former, and fully five-sixths of the latter to the south of
the equator, while no portion of the entire Asiatic conti-
nent extends so far south as to the equator. The equa-
torial regions of Africa and South America are accordingly
exposed to the direct rays of the sun, influenced only by
such modifications as the physical conformations of either
continent may effect, while tiie same region, lying in the
Indian seas, is tempered by the meliorating and more
equable temperature of the ocean, so that the vast re-
gions of Australia which lie witliin the same parallels of
latitude as the southern piirt of the African continent, are
now supplying to the British emigrant a temperate cli-
mate, more constant, but little more oppressive than the
mild summers of the British islands. Tlie isothermal
zones, which are thus made to take the place for certain
purposes, of the older geographical divisions of the globe,
must be ascertained by observations entirely different
from those of the mathematician and the astronomer.
The thermometer is the chief instrument of the isother-
mal observer, and by means of it the globe has been
divided into zones of equal annual mean temperature,
the perfect knowledge of which involves many imjjortant
practical results. The inflexions of these isothermal
lines is often very remarkable. On the South American
continent, for examide, the equator of tcmpeiature de-
viates entirely from the geograpliical equator, being in-
flected entirely to the nortli, and exceeding, by a mean
temperature of ten degrees, the true geogi'Hphical equa-
tor. In Africa also it lies to the noith of the geogra-
phical equator, tliough the isothermal inflexion is not to
the same extent ; wiiile in Asia the two equatorial lines
almost exactly coincide, tlie island of Borneo, and the
Indian seas, lyini,' directly on the line of the geographical
equator, and within the zone of highest temperature.
The deviations and inflections of the isothermal zones
are much less mai-ked where they occur within a large



PERIODICITY OF TEMPERATURE. 409

area of ocean, the sea presenting a medium readily and citaptek
equally heated, and less susceptible of local influences on -^-^VIIL
its temperature than the land. Even then, however, Temperahire
currents exercise a considerable influence, and occasional "' "'<^ <"=<'''"•
very marked inflexions of the isothermal zones occur
within the area of the ocean.

But in addition to the results which these observations Pcriodicitj-
involve as to the variations in the distribution of heat '.''re™^'"'^
over the earth's surface, they also lead to the considera-
tion of another remarkable class of phenomena connected
with the unequal distribution of heat over the year. In
the cold meridians, as is well known, a brief, but very
hot summer, and a cold winter occur, whereas in south-
ern latitudes of Europe and America, the cold of win-
ter is greatly moderated, and in the whole warmer meri-
dians of the globe, the difference between the tempera-
ture of summer and winter is greatly diminished. The
full importance of these observations of isothermal phe- importance
nomena is now fully appreciated ; but it is only by a °{,se^a{j™^'
very extensive and combined series of observations that
these comprehensive bearings will be made fully known,
and the direct clue obtained to the great lavs-s which
they involve. The meteorological observations which
are now established in so many parts of the world are
accumulating much valuable data for this purpose.
Private obsei-vers may also do much, and have already
furnished some important contributions to the same end,
so that the great scientific traveller to whom we owe the
foundation of these remarkable disclosures regarding the
laws that govern the universe, lias the satisfaction ot
himself observing a noble host of scientific pioneers ad-
vancing on the path which he had jiointed out, and fol-
lowing up his suggestive thoughts by the patient and
laborious analysis of scientific investigation.

But Humboldt has also taken into consideration other otiicrsonrces
sources of heat besides that which the earth derives from o'''»"'f-
the sun. He even reasons on the possil)ility of the earth
being a mere solid shell, inclosing a fluid mass, the heat



410



INTF.KNAL HEAT.



Internal
Eource of
heat.



CUAPTER and motion of wliich may alike affect the external opera-
■^•^^'^ tions that fall under our observation, while it is probably
also itself affected by the same laws which operate in
producing the ebb and flow of the sea. The facts which
prove the existence of an internal source of heat, alto-
gether apart from that which arises from the influence of
the solar rays, are familiar to us all. But its true influ-
ence or the degrees of heat which are manifested at any
regular depth, or under other defined circumstances, are
much more difficult to guage. " According to tolerably
uniform experiments in Artesian wells," our author re-
marks in his Cosmos, " it has been shown that the heat
increases on an average about 1° for every 54'5 feet. If
this increase can be reduced to arithmetical relations, it
will follow, as I have alreadj' observed, that a stratum
of granite would be in a state of fusion at a depth of
nearly twenty-one geographical miles, or between four
and five times the elevation of thp iiighest summit of the
Ilimalaya.

" We must distinguish in our globe three different
modes for the transmission of heat. The first is periodic,
and affects the temperature of the terrestrial strata ac-
cording as the heat penetrates from above downwards, or
from below upwards, being influenced by the different
positions of the sun and the seasons of the year. The
second is likewise an effect of the sun, although extremely
slow : a portion of the heat that has penetrated into the
equatorial regions moves in the interior of the globe
towards the poles, where it escapes into the atmosphere
and the remoter regions of space. The third mode of
transmission is the slowest of all, and is derived from the
secular cooling of the globe, and from the small portion
of the primitive heat which is still being disengaged from
the surfiice. This loss experienced by the central heat
must have been very considerable in the earliest epochs
of the earth's revolutions, but within historical periods it
lias hardly been appreciable by our instruments. The
Burface of the earth is therefore situated between the



TranrmissioD
of lieiit.



Cooling of
tjie globe.



TEMPEllATUKE OF THE SUKFACE. 411

glowing heat of tlie inferior strata and tlie universal chaitep.
regions of space, whose temperature is prohablj' below -^^^''l'-
the freezing point of mercury.

'' The periodic changes of temperature which have renctrutlon
been occasioned on the earth's surface by the sun's posi- t'mnperature.
tion and by meteorological processes, are continued in its
interior, although to a very inconsiderable depth. The
slow conducting power of the ground diminishes this loss
of heat in the winter, and is very favourable to deep-
rooted trees. Points that lie at very different depths on
the same vertical line attain the maximum and mini-
mum of the imparted temperature at very different
periods of time. The further they are removed from the
surface the smaller is this difference between the ex-
tremes. In the latitudes of our temperate zone (between
48° and 52°) the stratum of invariable temperature is stratum of
at a depth of from 59 to 64 feet, and at half that depth [e\npL,','.'iJure
the oscillations of the thermometer, from the influence
of the seasons, scarcely amount to half a degree. In tro-
pical climates this invariable stratum is only one foot
below the surface, and this fact has been ingeniously
made use of by Boussingault to obtain a convenient, and,
as he believes, certain determination of the mean tem-
perature of the air of different places. This mean tem-
perature of the air at a fixed point, or at a group of con-
tiguous points on the surface, is to a certain degree the
fundamental element of the climate and agricultural re-
lations of a district ; but the mean temperature of the
whole surflice is very different from that of the globe

itself. The questions so often agitated, whether the Changes of

, , . , • 1 1 1 J- J- tcmiierature.

mean temperature has experienced any considerable dii-

ferences in the course of centuries, whether the climate
of a country has deteriorated, and whether the winters
have not become milder and the summers cooler — can
only be answered by means of the thermometer ; this
instrument has, however, scarcely been invented more
than two centuries and a half, and its scientific applica-
tion hardly dates back 120 years. The nature and no-



412 STABILITY OF THE EARTIl's HEAT.

CHAPTER velty of the means interpose, therefore, very narrow
xxyi^ii. ]irnits to our investigation regarding the temperature of
Intprnal lipat the air. It is quite otlierwise, liowever, witli the solu-
tion of the great problem of the internal heat of the
whole earth. As we may judge of uniformity of tem-
perature from the unaltered time of vil)ration of a pen-
dulum, so we may also learn from the unaltered rotatory
velocity of the earth the amount of stability in the meai'
temperature of our glol)e. Tiiis insight into the rel? •
tions between the length of the day and the heat of the
earth is the result of one of the most brilliant applica-
tions of the knowledge we had long possessed of the
movement of the heavens to the thermic condition of
our planet. The rotatory velocity of the earth depends

Relations of on its Volume ; and, since by the gradual cooling of the

motion and , ,. . ' ... , , ,

lie.1t. mass by radiation, the axis of rotation would become

shorter, the rotatory velocity would necessarily increase,

and the length of the day diminish, with a decrease of

the temperature. From the comparison of the secular

inequalities in the motions of the moon with the eclipses

observed in ancient times, it follows that since the time

of Ilipparchus, that is, for full 2000 years, the length of

the jlay has certainly not diminished by the hundredth

part of a second. The decrease of the mean heat of the

globe during a period of 2000 years has not, therefore,

taking the extremest limits, diminished as much as

l-30Gth of a degree of Fahrenheit.

Invp.riiibiiity n rpj^jg invariability of form ])resupposes also a gi-eat

invariiibiiity in the distribution of relations of density

in the interior of the globe. The translatory movements,

which occasion the eruptions of our present volcanoes,

and of ferruginous lava, and the filling up of previously

empty fissures and cavities with dense masses of stone,

are consequently only to be regarded as slight superficial

phenomena affecting merely one portion of tiie carth'p

crust, which, from tiieir smallness when compared to the

earth's radius, become wholly insignificant."

Such are some of the remarkable readings of nature,



READINGS OF NATURE. 413

as we may term them, which the venerable pliilosoplicr chaptkr
has acliieved by tlie careful study of the phenomena ^'^^
presented to his observation. The interpretation is not Differenrc <>t
indeed to be accepted entirely as an established law.
Various opinions have been advanced to account for the
internal heat of the planet, and its increasing tempera-
ture at various depths below the surface. Not the least
important or curious of these relate to the mysterious
principle of magnetism. Changes of temperature, it is
now well ascertained, do call forth magnetic and electric
currents ; but the phenomena exhibited by terrestrial
magnetism are still only very partially understood, and
these, as well as many other great natural laws, must
await the labours of others for their complete elucida-
tion. They bear, however, to an extent of which we Magnetic
, . ^1 1 • , cuirenU.

are yet only very imperiectly aware, on the nnportant

subject elucidated by our author in his" Researches on
the Causes of the Inflexion of the Isothermal Lines ;"'
and which he has extended as an addition to a previous
valuable " Memoir" on the same subject. Some of the
important views indicated in these Researches have been
traced on a previous page. But the entire treatise is of
the utmost value to the natural philosopher, as well as
of direct practical worth in relation to many depart-
ments of our modern political economy. It contains the Practical
most important exposition of philosophic views on cli-
mate and the distribution of temperature which have
ever been set forth by any single individual. The full
value of these researches are still very partially appre-
ciated, and they have yet almost wholly to be turned to
their full practical account in relation to navigation,
agriculture, colonization, and the various economic forms
to which the researches of the profound observer are re-
ducible for the amelioration and progress of his race.

Such is a slight sketch of Baron Humboldt's Researches
in Central Asia, and of some of the valuable facts and
important deductions which have already resulted from
his labours. Many of his speculations are too profound,



414



MODE OF ARRANGEMENT,



Abstract
fjieculations.



Fnn'.ts o:
system.



CHAPTER and of too abstract a character, to be readily reducible to

a popular form. They are, moreover, advanced, in his

most extensive works, in a form which adds considerably
to the difficulty of the ordinary student in attempting
to master them. A want of method has, indeed, been
complained of in all his works, pertaininc^ not to the ac-
curacy of his scientific observations, but to the absence
of any well defined system in their arrangement. Other
difficulties occur to the student who seeks to master liis
discoveries in the form in which they were originally
presented. One of the most practical of these is thus
referred to by Dr. Alison: "Akin to this is another
fault of a more irremediable kind, as it originates in the
varied excellences of the author, and the vast store of in-
formation on many different subjects which lie brings to
bear on the subject of his travels. He has so many
topics of which he is master himself, that he forgets with
how few, comparatively, his readers are familiar ; he
sees so many objects of inquiry — physical, moral, and
political — in the countries which he visits, that he be-
comes insensible to the fact that, though each probably
possesses a certain degree of interest to each reader, yet
it is scarcely possible to find one to whom, as to himself,
they are all alike the object of eager solicitude and
anxious investigation. Hence, notwithstanding his
attempt to detach his Personal Narrative from the
learned works which contain the result of his scientific
researches, he has by no means succeeded in effecting
their separation. The ordinary reader, who has been
fascinated by liis glowing description of trojjical scenery,
or his graphic picture of savage manners, is, a few pages
on, chilled by disquisitions on the height of the baro-
meter, the disc of the sun, or the electricity of the
atmosphere ; while the scientific student, who turns to
Jiis works for information on his favourite objects of
study, deems them strangely interspersed with rhap-
sodies on glowing sunsets, silent forests, and sounding
cataracts. It is scarcely possible to find a reader to



Cnattractive
Biibjtcts.



HUMBOLDT'S DISTINCTION. 415

whom all these ol>jects are equally interesting ; and chaptfr
therefore it is scarcely be to expected that his travels, ^J^^iVlll.
unrivalled as their genius and learning are, will ever be
the object of general popularity."

The fault, it will be seen, is one fully as much of the ciscursire
reader as the author. Nevertheless it is such as will treatment of
ever in some respects preclude the great mass of readers
from studying the discoveries and researches of this dis-
tinguished scientific traveller directly from his own
works. Like our own Newton, his vast contributions
to science may be compared to a treasure of gold, the
value of which cannot be augmented, but it may be
reduced into a more convenient form of currency.
Such is the process which is being applied to the pro-
found researches of Alexander Von Humbolt, and already
we see his works assuming a popular form, and circulat-
ing throughout the various countries of Europe, dissemi-
nating knowledge and instigating to further investiga-
tion.

Any formal eulogy on the great and illustrious author Distinction
of these Researches would be entirely out of place here, tiior.
It has been his fortune to experience what few profound
scientific discoverers have done. Surviving to the extreme
verge of the usual lot of human life, he has enjoyed in
the calm serenity of an honoured old age the full appre-
ciation of the labours of a life-time, and has been able to
accomplish much, though he has not completed all the
gigantic projects of his vast ideal. He thus introduces
the comprehensive work, which he has offered as a
" Sketch of a Physical Description of the Universe," in Physical
the preface which he addresses to his own fellow coun- of the uni-
trymen : — " In the late evening of an active life I offer ■^^^''*^-
to the German public a work, whose undefined image
has floated before my mind for almost half a century.
I have frequently looked upon its completion as imprac-
ticable, but as often as I have been disposed to relinquish
the undertaking, I have again — although perhaps im-
prudently — resumed the task. This wovk I now present



416



HIGH OBJECTS OF STUDY.



Scientific
occupations.



Objects
aimed at.



ClI.^PTER to my contemporaries, with a diffidence inspired by a
^ ^^ ^^ '' just mistruht of my own powers, whilst I wouhl willingly
t'urn;t't that writings long expected are usually received
with less indulgence.

"Although the outward relations of life, and an irre-
sistible impulse towards knowledge of various kinds, have
led me to occupy myself for many years — and apparently
exclusively — with separate branches of science, as, for
instance, with descriptive botany, geognosy, chemistry,
astronomical determinations of position, and terrestrial
magnetism, in order that I might the better prepare my-
self for the extensive travels in which I was desirous of
engaging, the actual object of my studies has neverthe-
less been of a liigher character. The principal impulse
by which I was directed, was the earnest endeavour to
comprehend the phenomena of phj'sical objects in their
general connection, and to represent nature as one great
whole, moved and animated by internal forces. My in-
tercourse with highly-gifted men early led rae to discover
that, without an earnest striving to attain to a know-
ledge of special branches of study, all attempts to give a
gi'and and general view of the universe would be nothing
more than a vain illusion. These special departments
in the great domain of natural science are, moreover,
capable of being reciprocallj' fructified by means of the
appropriative forces by which they are endowed. Descrip-
tive botany, no longer confined to the narrow circle of the
determination of genera and species, leads the observer
who traverses distant lands and loft}^ mountains to the
study of the geographical distribution of plants over the
earth's surface, according to distance from the equator
and vertical elevation above the sea. It is futher neces-
sary to investigate the laws which regulate the differences
of temperature and climate, and the njcteorological pro-
cesses of the atmosphere, before we can hope to explain
the involved causes of vegetable distribution; and it is
thus that the observer wlio earnestly i)ursues the path of
kuowledge is led from one class of phenomena to another,



licpcriptive
botany.



GREAT ADVANTAGES. 4] 7

by means of the mutual dependence and connection chapter
existing between tliem. XXVlll.

" I have enjoyed an advantage which few scientific Advantages
travellers have shared to an equal extent, namely, that veUer.
of having seen not only littoral districts, such as are alone
visited by tlie majority of those wlio take part in voyages
of circumnavigation, but also tbose portions of tlie interior
of two vast continents wliich ])resent most striking con-
trasts, manifested in the Alpine tropical landscapes of
South America, and the dreary wastes of the steppes in
Northern Asia. Travels, undertaken in districts such as Enooiiras©-
these, could not fail to encourage the natural tendency ge'nera'uza
of my mind towards a generalization of views, and to tion.
encourage me to attempt, in a special work, to treat of
the knowledge wliich we at present possess, regarding
the sidereal and terrestrial phenomena of the Cosmos in
their empirical relations. The hitherto undefined idea of
a physical geography has thus, by an extended and
perhaps too boldly imagined plan, been comprehended,
under the idea of a physical description of the universe,
embracing all created things in the regions of space and
in the earth,

" The very abundance of the materials which are Abundant
presented to the mind for arrangement and definition,
necessarily impart no inconsiderable difficulties in the
choice of the form under which such a woik must be
presented, if it would aspire to the honour of being re-
garded as a literary composition. Descriptions of nature pifficnlties
ought not to be deficient in a tone of life-like truthful- appUcation.
ness, whilst the mere enumeration of a series of general
results is productive of a no less wearying impression
than the elaljorate accumulation of the individual data
of observation. I scarcely venture to hope that I have
succeeded in satisfying these various requirements of
composition, or that I have myself avoided the shoals
and breakers which I have known liow to indicate to
others. My faint hope of success rests upon the special
indulgence which the German public have bestowed upon



418



CONCLUSION.



CHAPTER

xxvin.



I/Bctures at
Paris and
Berlin.



a small work bearing the title of Ansichten der NattiVy
whicli I published soon after my return from Mexico.
In the work on the Cosmos on which I am now en-



Online LibraryAlexander von HumboldtThe travels and researches of Alexander von Humboldt → online text (page 34 of 35)