Man newly created, and even the ignorant man at this day beholds the
extent and nature of the universe only by the simple organ of light: to
him the earth is but a solid body, whose volume is unbounded, and whose
extent is without limits, of which he can only survey small superficial
spaces: while the sun and planets seem to be luminous points, of
which the sun and moon appear to be the only objects worthy regard
in the immensity of the heavens. To this false idea on the extent of
nature and the proportions of the universe is joined the still more
disproportionate sentiment of superiority. Man, by comparing himself
with other terrestrial beings, feels that he ranks the first, and hence
he presumes that all was made for him; that the earth was created only
to serve for his habitation, and the heavens for a spectacle; and
in short the whole universe ought to yield to his necessities, and
even his pleasures. But in proportion as he makes use of that divine
light, which alone ennobles his being; in proportion as he obtains
instruction, he is forced to abate his pretensions; he finds himself
lessened in proportion as the universe increases in his ideas, and
it becomes demonstrable to him, that the earth, which forms all his
domain, and on which unfortunately he cannot subsist without trouble
and sorrow, is as small with respect to the universe, as he is with
respect to the Creator. In short, from study and application, he finds
that there does not remain a possible doubt, that this earth, large
and extensive as it may seem to him, is but a moderate sized planet, a
small mass of matter, which, with others, has a regular course round
the sun: for as it appears our globe is at the distance of at least 33
millions of leagues, and the planet Saturn at 313 millions, the natural
conclusion is, that the extent of the sun's empire is a sphere, whose
diameter is 627 millions of leagues, and that the earth, relative to
this space, is not more than a grain of sand to the volume of the globe.
However, the planet Saturn, although the furthest from the sun, is not
by any means near the confines of his empire: his limits extend much
further, since comets pass over spaces beyond that distance, as may be
estimated by the time of their revolutions: a comet which like that
of the year 1680 revolves round the sun in 575 years must be 15 times
more remote from him than Saturn; for the great axis of its orbit is
138 times greater than the distance from the earth to the sun. Hence we
must still augment the extent of the solar power 15 times the distance
from the sun to Saturn, so that all the space in which the planets are
included is only a small province of his domain, whose bounds should be
placed at least 138 times his distance from the earth.
What immensity of space! What quantity of matter! For independently
of the planets, there is a probability of the existence of 400 or 500
comets, perhaps larger than the earth, which run over the different
regions of this vast sphere of which the terrestrial globe only
constituting a part, a unity on 191,201,612,985,514,272,000, a quantity
represented by numbers, which imagination cannot attain or comprehend.
Nevertheless, this enormous extent, this vast sphere, is yet only a
very small space in the immensity of the heavens; each fixed star is
a sun, a center of a sphere equally as extensive; and as we reckon
more than 2000 of these fixed stars perceived by the naked eye, and as
with telescopes we can discover so much the greater number as these
instruments are more powerful; the extent of the universe appears to
be without bounds and the solar system forms only a province of the
universal empire of the Creator; an infinite empire like himself.
Sirius, the most brilliant fixed star, and which for that reason may
be regarded as the nearest sun to our's, affords to our sight only a
second of annual parrallax on the whole diameter of the earth's orbit,
and is therefore at the distance of 6,771,770, millions of leagues
distant from us, that is, 6,767,216 millions of leagues from the limits
of the solar system, such as we have assigned it after the depth to
which the comets immerse. Supposing then, there is an equal space from
Sirius to that which belongs to our sun, we shall perceive that we must
extend the limits of our solar system 742 times more than it is at
present, as far as the aphelion of the comet, whose enormous distance
from the sun is nevertheless only a unit on 742 of the total diameter
of the solar system.
Leagues.
Distance from the earth to the Sun 33,000,000
Distance from Saturn to the Sun 313,000,000
Distance from the aphelion of the Comet to the Sun 4,554,000,000
Distance from Sirius to the Sun 6,771,770,000,000
Distance of Sirius to the point
of the aphelion of the Comet,
supposing that in ascending
from the sun the comet pointed
directly towards Sirius (a supposition
which diminishes the distance as much as
possible) 6,767,216,000,000
One half the distance from Sirius to the
Sun, or the depth of the solar and sircin
system 3,385,885,000,000
Extent beyond the limits of the comet's
aphelion 3,331,331,000,000
Which being divided by the distance of the
comet's aphelion, gives about 742-1/2
We can form another idea of our immense distance from Sirius, by
recollecting that the sun's disk forms to our sight an angle of 32
minutes, whereas that of Sirius forms only that of a second; and Sirius
being a sun like ours, which we shall suppose of equal magnitude, since
there is no reason to conceive it larger or smaller, it would appear
to us as large as the sun, if it were but a like distance. Taking
therefore two numbers proportional to the square of 32 minutes, and to
the square of a second, we shall have 3,686,400 for the distance of the
earth to Sirius, and one for its distance to the sun; and as this unit
is equal to 33 millions of leagues, we see how many millions of leagues
Sirius is distant from us, since we must multiply these 33 millions by
3,686,400; and if we divide the space between these two neighbouring
suns, although at so great a distance, we shall see that the comets
might be removed to a distance 1,800,000 times greater than that of
the earth to the sun without quitting the limits of the solar universe,
and without being subjected to other laws than that of our sun, and
hence it may be concluded that the solar system for its diameter has
an extent, which, although prodigious, nevertheless, forms only a very
small portion of the heavens; and we must infer a truth therefrom but
little known, namely, that from the sun, the earth and all the other
planets, the sky must appear the same.
When in a serene and clear night we contemplate all those stars with
which the celestial vault is illuminated, it might be imagined that
by being conveyed into another planet more remote from the sun, we
should see these glittering stars larger, and emitting a brighter
light, since we should be so much nearer to them. Nevertheless, the
calculation we have just made demonstrates that if we were placed in
Saturn, which is 300 millions of leagues nearer Sirius, it would appear
only an 194,021st part bigger, an augmentation absolutely insensible;
from which it must be concluded, that the heaven, with respect to all
the planets, has the same aspect as it has to the earth. Therefore if
even there should exist comets whose periods of revolution might be
double, or treble the period of 575 years, the longest known to us; if
even the comets in consequence thereof, immerse at a depth ten times
greater, there would still be a space 74 or 75 times deeper, to reach
the last confines, as well of the solar system, as of the sirian; so
that by allowing Sirius as much magnitude as our sun has, and supposing
in his system as many or more cometary bodies than there are comets
existing in the solar, Sirius will govern them as the sun governs his,
and there will remain an immense interval between the confines of the
two empires; an interval which appears to be no more than a desart in
the vast space, and which must give a suspicion that cometary bodies
do exist, whose periods are longer, and which are to a much greater
distance than we can determine by our actual knowledge. Sirius may
also be a sun much larger and more powerful than ours; and if that is
the case, it must throw the borders of his domain so much the further
back by approaching them to us, and at the same time retrench the
circumference of the sun.
I cannot avoid presuming, that in this great number of fixed stars,
which are all so many suns, there are some greater and others smaller
than ours; others more or less luminous, some nearer, which are
represented to us by those stars called by astronomers, _stars of the
first magnitude_, and many others more remote, which for that reason
appear to us smaller. The stars called _nebulous_ seem to want light
and fire, and to be only half lighted; those which appear and disappear
alternately are, perhaps, of a form flattened by the violence of the
centrifugal force in their motion of rotation, and are perceiveable
only when they are in the full, disappearing when they are sideways.
In this grand order of things, and in the nature of the stars, there
are the same varieties, and the same differences, in number, size,
space, motion, form, and duration; the same relation, the same degrees,
and the same connection, as are found in all the other orders of the
creation.
Each of the suns being endowed like ours, and like all matter, with
an attractive power, which extends to an indefinite distance, and
decreases, as the space increases, analogy leads us to imagine that
within each of their spheres there exists a great number of opaque
bodies, planets, or comets, which circulate round them, but which being
much smaller than the suns which serve them for heat, they are beyond
the reach of our sight.
It might be imagined that comets pass from one system to the other,
and that if they happened to approach the confines of the two empires
they would be attracted by the preponderating power, and forced to
obey the laws of a new master. But, by the immensity of space which
is beyond the aphelion of our comets, it appears that the Sovereign
Ruler has separated each system by immense desarts, a thousand and
a thousand times larger than all the extent of known spaces. These
desarts, which numbers cannot fathom the depth of, are external and
invincible barriers, that all the powers of created nature cannot
surmount. To form a communication from one system to the other, and for
the subjects of one to pass into the other, it would be requisite that
the centre was not immoveable, for the sun, the head of the system,
changing place, would draw with it in its course all the bodies which
depend thereon, and hence might approach and invade another demesne.
If its route were directed towards a weaker star, it would commence by
carrying off the subjects of its most distant provinces, afterwards
those more interior, and would oblige them all to increase its train by
revolving round it; and its neighbour thus deprived of its subjects, no
longer having planets nor comets, would lose both its light and fire,
which their motion alone can excite and support; hence this detached
star, being no longer maintained in its place by the equilibrium of its
forces, would be obliged to change nutrition, by changing nature, and
becoming an obscure body, would, like the rest, obey the power of the
conqueror, whose fire would increase in proportion to the number of its
conquests.
For what can be said on the nature of the sun but that it is a body of
prodigious volume, an enormous mass of matter penetrated by fire, which
appears to subsist without aliment, and which resembles a metal or a
solid body in incandescence? And from whence can this constant state
of incandescence, this continually renewed production of fire proceed,
whose consumption does not appear to be supported by any aliment, and
whose deperdition is at least insensible, although constant for such
a great number of years? Is there, or can there be, any other cause
of the production of this permanent fire, but the rapid motion from
the strong pressure of all bodies, which revolve round this common
heat, and which heats and sets fire to it, like a wheel rapidly
turned round its axis? The pressure, which they exercise by virtue of
their weight is equivalent to the friction, and even more powerful,
because this pressure is a penetrating power, which not only rubs the
external surface but all the internal parts of the mass: the rapidity
of their motion is so great that the friction acquires a force almost
infinite, and consequently sets the whole mass of the axis in a state
of incandescence, of light, of heat, and of fire, which hence has no
need of aliment to be supported, and which, in spite of the deperdition
each day made by the emission of light, may remain for ever without any
sensible alteration, other suns rendering as much light to ours as it
sends to them, and no part of the smallest atom of fire, or any other
matter, being lost in a system where all is attracted.
If from this sketch of the great table of the heavens, and in which
I have only attempted to represent to myself the proportion of the
spaces, and that of the motion of bodies which travel over them;
if from this point of view, to which I only raised myself to see
how greatly nature must be multiplied in the different regions of
the universe, we descend to that proportion of space which we are
better acquainted with, and in which the sun exercises its power,
we shall discover, that although it governs all bodies therein, it,
nevertheless, has not the power of vivifying them, nor even that of
supporting life and vegetation.
Mercury, which is the nearest to the sun, nevertheless receives only
a heat 400 times stronger than that of the earth, and this heat, so
far from being burning, as it has always been supposed, would not be
strong enough of itself to support animated nature, for the actual
heat of the sun on the earth being only 1/50 part of the heat of the
terrestrial globe, that of the sun on Mercury consequently is only 1/8
part of the actual heat of the earth. Now if 7/8 parts were subtracted
from the heat which is at present the temperature of the earth, it is
certain animated nature would be checked, if not entirely extinguished.
Since the sun alone cannot maintain organised nature in the nearest
planet, how much more aid must it require to animate those at a greater
distance? To Venus it only sends a heat 2/50 times stronger than that
it sends to the earth, which instead of being strong enough to support
animated nature, would not certainly suffice to maintain the liquidity
of water, nor perhaps even the fluidity of air, since our actual
temperature would be refrigerated to 2/49, which is very near the
term 1/25 we have given as the external limit of the slightest heat,
relative to living nature. And with respect to Mars, Jupiter, Saturn,
and all their satellites, the quantity of heat which the sun sends to
them, in comparison with that which is necessary for the support of
nature, which may be looked upon as of little effect, especially in the
two larger planets, which, nevertheless, appear to be the essential
objects of the solar system.
All the planets, therefore, have always been volumes (as large as
useless) of matter more than dead, profoundly frozen, and consequently
places uninhabited and uninhabitable for ever, if they do not include
within themselves treasures of heat much superior to what they receive
from the sun. The heat which our globe possesses of itself, and which
is 50 times greater than that which comes to it from the sun, is, in
fact, the treasure of nature, the true fund which animates us as well
as every being: it is this internal heat of the earth which causes
all things to germinate and to develope; it is that which constitutes
the element of fire, properly called an element, which alone gives
motion to other elements, and which if it was reduced to 1/20 could
not conquer their resistance, but would itself fall into an inertia.
Now this element, this sole active power, which may render the air
fluid, the water liquid, and the earth penetrable, might it not have
been given to the terrestrial globe alone? Does analogy permit us to
doubt that the other planets do not likewise contain a quantity of
heat, which belongs to them alone, and which must render them capable
of receiving and supporting living nature? Is it not greater and more
worthy the idea we ought to have of the Creator, to suppose that there
every where exists beings who acknowledge his power and celebrate his
glory, than to depopulate all the universe, excepting the earth, and
to despoil it of all beings, by reducing it to a profound solitude,
in which we should only find a desart space, and frightful masses of
inanimate matter.
Since the heat of the sun is so small on the earth, and other planets,
it is necessary that they should possess a heat belonging solely to
themselves, and our enquiry must be to see whence this heat proceeds
which alone can constitute in them this element of fire. Now where
shall we be able to discover this great quantity of heat if it be
not in the source itself, in the sun alone? for the matter of which
the planets have been formed and projected by a like impulsion will
have preserved their motion in the same direction, and their heat
in proportion to their magnitude and density. Whoever weighs these
analogies, and conceives the power of their relations, will not
doubt that the planets have issued from the sun by the stroke of a
comet, because in the solar system comets only could have power and
sufficient motion, to communicate a similar impulsion to the masses
of matter which compose the planets. If to all these circumstances we
unite that of the innate heat of the earth, and of the insufficiency
of the sun to support nature, we must rest persuaded, that in the
time of their formation the planets and earth were in a state of
liquefaction, afterwards in a state of incandescence, and at last in
a successive state of heat, always decreasing from incandescence to
actual temperature, for there is no other mode of conceiving the origin
and duration of this heat peculiar to the earth. It is difficult to
imagine that the fire, termed central, can subsist at the bottom of the
globe without air (that is, without its first aliment, and from whence
this fire should proceed, which is supposed to be shut up in the centre
of the globe), because what origin, what source shall we then find
for it? Descartes has imagined the earth and planets were only small
incrusted suns; in other words, suns entirely extinguished. Leibnitz
has not hesitated to pronounce that the terrestrial globe owes its
source, and the consistence of its matters, to the element of fire; yet
these two great philosophers had not the assistance of these numerous
circumstances and observations which have been acquired and collected
in our days, and which are so well established that it appears more
than probable that the earth, as well as the planets, were projected
out of the sun, and being consequently of a like matter, which was
at first in a state of liquefaction they obeyed the centrifugal
power, at the same time that it collected itself together by that of
attraction, which has given a round form to all the planets under the
equator, and flattened under the poles, on account of the variety of
their rotation; that afterwards this fire being gradually dissipated,
the benign temperature, suitable to organized nature, succeeded in
different planets according to the difference of their thickness or
density. If there should be other particular causes of heat assigned
for the earth and planets, which might combine with those whose effects
we have calculated, our results are not less curious, nor less useful
to the advancement of science; and we shall here only observe, that
those particular causes may prolong the time of the refrigeration of
the globe, and the duration of living nature, beyond the terms we have
indicated.
But I may be asked is this Theory equally as well founded in every
point which serves for its basis; is it certain, according to your
experiments, that a globe, as large as the earth, and composed of
the same matters, cannot refrigerate from incandescence to actual
temperature in less than 74,000 years, and that in order to become
heated to the point of incandescence a 15th of this time, that is
5000 years, would be required: and also that it should be surrounded
all that time by the most violent fire; if so, there are as you say
strong presumptions that this great heat of the earth could not have
been communicated to it from a distance, and that consequently the
terrestrial matter formerly made a part of the mass of the sun; but it
does not appear equally proved that the heat of this body on the earth
is at present but 1/50 part of the heat of the globe. The testimony
of our senses seems to refute this opinion, which you lay down as a
certain truth, for although we cannot doubt that the earth has an
innate heat, which is demonstrated by its always equal temperature, in
all deep places where the coldness of the air cannot communicate; yet
does it result that this heat, which appears of moderate temperature,
is greater than that of the sun which seems to burn us?
To all these objections I can give full satisfaction, but let us first
reflect on the nature of our sensations. A very slight, and often
imperceptible, difference in the causes which affect us, produces
considerable ones in their effects. Is there any thing which comes
nearer to extreme pleasure than grief? and who can assign the distance
between the lively irritation by which we are moved with delight, and
the friction which gives us pain? between the fire which warms and that
which burns? between the light which is agreeable to our sight and that
which blinds us? between the savour which pleases our taste and that
which is disagreeable? between the smell of which a small quantity
will at first be agreeable and yet soon after create nausea? We must
therefore cease from being astonished that a small augmentation of
heat, such as 1/50 should appear so striking.
I do not pretend positively to assert that the innate heat of the
earth is really 49 times greater than that which comes to it from the
sun: for as the heat of the globe belongs to all terrestrial matter,
we have no means of separating it, nor consequently any sensible and
real limits to which we might relate it. But even if the solar heat be
greater or smaller than we have supposed, relative to the terrestrial
heat, our theory would only alter the proportion of the results.
For example, if we include the whole extent of our sensations of the
greatest heat to the greatest cold, within the limits given by the
observations of M. Amontons, that is, between seven and eight, and at
the same time suppose that the heat of the sun can alone produce this
difference of our sensations, we shall from thence have the proportion
of 8 to 1 of the innate heat of the terrestrial globe to that which
proceeds from the sun; and consequently the compensation which this
heat of the sun actually makes on the earth, would be 1/8 and the
compensation which it made in the time of incandescence will have
been 1/260: adding together these two terms, we have 26/900, which
multiplied by 12-1/2, the half of the sum of all the terms of the
diminution of heat, gives 325/400 or 5/8 for the total compensation
made by the sun's heat during the the period of 74047 years of the
refrigeration of the earth to actual temperature. And as the total
loss of the innate heat is to the total compensation in the same ratio
as the time of the period of refrigeration, we shall have 25 : 1-5/8
:; 74047 : 4813-1/25, so that the refrigeration of the globe of the
earth instead of having been prolonged only 770 years, would have been
4813-1/25 years; which joined to the longest prolongation, the heat of
the moon would also produce in this supposition, would give more than
5000 years.
If we adopt the limits laid down by M. de Marian, which are from 31 to
32, and suppose that the solar heat is no more than 1/32 of that of the
earth, we shall have only 1/4 of this prolongation, about 1250 years,
instead of 770, which gives the supposition of 1/50 which we have
adopted.
But if we suppose that the sun's heat is only 1/250 of that of the
earth, as appears to result from the observations made at Paris, we
should have for the compensation of the incandescence 1/6250 and 1/250
for the compensation to the end of the period of 7407 years of the
refrigeration of the terrestrial globe to actual temperature, and we
should find 17/250 for the total compensation made by the heat of the
sun during this period, which would give only 154 years, or the 5th
part of 770 years for the time of the prolongation of refrigeration.
And likewise, if in the place of 1/50 we suppose that the solar
heat was 1/50 of the terrestrial, we should find that the time of
prolongation would be five times longer, that is 3850 years; so that
the more we endeavour to increase the heat which comes to us from the
sun relative to that which emanates from the earth, the more we shall
extend the duration of nature, and date the antiquity of the earth
further back; for by supposing the heat of the sun was equal to the
innate of the globe, we should find that the time of prolongation would
be 38504 years, which consequently gives the earth a greater antiquity
of 38 or 39000 years.
If we cast our eye on the table which M. de Mairan has calculated with
great exactness, and in which he gives the proportion of the heat which
comes to us from the sun, to that which emanates from the earth in all
climates, we shall discover a well attested fact, which is, that in
all climates where observations have been made, the summers are equal,
whereas the winters are prodigiously unequal; this learned naturalist,
attributes this constant equality of the intensity of heat in summer in
all climates to the reciprocal compensation of the solar heat, and from
the heat of the emanations of the central fire.
All naturalists who have employed themselves on this subject agree
with me that the terrestrial globe possesses of itself a heat
independently of that which comes from the sun. Is it not evident that
this innate heat should be equal at every place on the surface of the
globe, and that there is no other difference in this respect than that
which results from the swelling of the earth at the equator, and of its
flatness under the poles? A difference, which being in the same ratio
nearly as the two diameters, does not exceed 1/230, so that the innate
heat of the terrestrial spheriod must be 1/230 times greater under
the equator than under the poles. The deperdition which is made, and
the time of refrigeration must, therefore, have been quicker, or more
sudden, in the northern climates, where the thickness of the globe is
not so great as in the southern climates, but this difference of 1/230
cannot produce that of the inequality of the central emanations, whose
relation to the heat of the sun in winter being equal 50 to 1 in the
adjacent climates to the equator, is found double to the 27th degree,
triple to the 35th, quadruple to the 40th, tenfold to the 49th, and
35 times greater to the 60th degree of latitude. This cause, which
presents itself, contributes to the cold of the northern climates, but
it is insufficient for the effect of the inequality of the winters,
since this effect would be 35 times greater than its cause to the 60th
degree, and even excessive in climates nearer the poles; at the same
time it would in no part be proportional to this same cause.
On the other hand there is not any foundation for supposing that in
a globe which has received, or which possesses a certain degree of
heat, there might be some parts of it much colder than others. We are
sufficiently acquainted with the progress of heat and the phenomena of
its communication, to be convinced that it is every where distributed
alike, since by placing a cold body on one that is hot, the latter
will communicate to the other sufficient heat to render heat of the
same degree of temperature in a short time. It must not, therefore, be
supposed that towards the poles there are strata of colder matters less
permeable to the heat than in other climates, for of whatever nature
they may be supposed to be, experience has demonstrated that in a very
short time they would become as hot as the rest.
It is evident that great cold in the north does not proceed from these
pretended obstacles which might oppose themselves to the issue of
heat, nor from the slight difference which that of the diameters of
the terrestrial spheroid must produce; but it appears to me, after
much reflection upon it, that we ought to attribute the equality of
the summers, and the great inequality of the winters to a much more
simple cause, but which, notwithstanding, has escaped the notice of all
naturalists.
It is certain that as the native heat of the earth is much greater than
that which comes to it from the sun, the summers ought to appear nearly
equal every where, because this same heat from the sun makes only a
small augmentation to the stock of real heat which the earth possesses;
and consequently if this heat issuing from the sun, be only 1/[T.N.]
of the native heat of the globe, the greater or less stay of it on
the horizon, its greater or less obliquity on the climate, and even
its total absence, would only produce one-fiftieth difference on the
temperature of the climate, and hence the summers must appear, and are,
in fact, nearly equal in all the climates of the earth. But what makes
the winters so very unequal is the emanations of this internal heat of
the globe being in a great measure suppressed as soon as the cold and
frost bind and consolidate the surface of the earth and waters.
[T.N.: denominator missing from printed version.]
This heat which issues from the globe, decreases in the air in
proportion, and in the same ratio as the space increases, and the
sole condensation of the air by this cause is sufficient to produce
cold winds, which acting against the surface of the earth, bind and
freeze it. As long as this confinement of the external strata of the
earth remains, the emanations of the internal heat are retained, and
the cold appears to be, nay in fact is, very considerably increased by
this suppression of a part of this heat; but as soon as the air becomes
milder, and the superficial strata of the globe loses its rigidity,
the heat, retained all the time of the frost, issues out in greater
abundance than in climates where it does not freeze, so that the sum
of the emanations of the heat becomes equal and every where alike; and
this is the reason that plants vegetate quicker, and the harvest is
reaped in much less time in northern countries; and for the same reason
it is, that often at the beginning of summer we feel such considerable
heats.
If there were any doubt of the suppression of the emanations of the
internal heat by the effect of frost, we might easily be convinced
of the fact; for it is a circumstance universally known, that after
a frost, we may perceive snow to thaw in pits, acqueducts, cisterns,
quarries, subterraneous vaults or mines, when even these depths, pits
or cisterns, contain no water; the emanations of the earth having
their free issue through these kinds of vents, the ground which covers
this top is never frozen so strong as the open land; to the emanations,
it permits their general course, and their heat is sufficient to melt
the snow, especially in hollow places, at the same time that it remains
on all the rest of the surface where the earth is not excavated.
This suppression of the emanations of the native heat of the earth is
not only made by the frost, but likewise by the simple binding of the
earth, often occasioned by a less degree of cold than that which is
necessary to freeze the surface; there are very few countries where it
freezes in the plains beyond the 35th degree latitude, particularly in
the northern hemisphere. It appears, therefore, that from the equator,
as far as the 35th degree, the emanations of the terrestrial heat
having always their free issue, there ought to be in that part little
or no difference between winter and summer, since this difference
proceeds only from two causes, both too slight to produce any sensible
effect. The first cause is the difference of the solar action, but as
this action is itself much smaller than that of the terrestrial heat,
its difference is too inconsiderable to be regarded as any thing. The
second cause is the thickness of the globe, which towards the 35th
degree, is near 1/590th part less than at the equator, but even this
difference can only produce a very slight effect, since at 35 degrees
the relation of the emanations of the terrestrial to the solar heat is
in summer from 33 to 1, and in winter from 153 to 1, which gives 186 to
2 or 93 to 1. From hence it can only be owing to the consolidation of
the earth occasioned by the cold, or even to the cold produced by the
durable rains which fall in these climates, that we can attribute this
difference between winter and summer; the binding of the earth by cold
suppresses a part of the emanations of the internal heat, and the cold,
always renewed by the fall of rain, diminishes its intensity; these two
causes, therefore, together produce the difference between winter and
summer.
After having proved that the heat which comes to us from the sun
is greatly inferior to the native heat of our globe; after having
explained that, by supposing it only 1/50 part, the refrigeration of
the globe to actual temperature cannot be made but in 75,832 years;
after having demonstrated that the time of this refrigeration would
still be longer, if the heat sent from the sun to the earth were in
a greater relation, namely, of 1/25 or 1/10 instead of 1/50, we
cannot be blamed for having adopted that proportion which appears the
most plausible from physical reasonings, and at the same time the
most probable, as it does not extend too far back the time of the
commencement of nature, which we have fixed at 37 or 38,000 years,
dating it from the first day.
I nevertheless acknowledge that this time, all considerable as it
is, does not appear sufficiently long for certain changes, certain
successive alterations, which Natural History demonstrates to have
taken place, and which seem to have required a still longer course of
centuries; and from which I should be inclined to imagine, that, in
reality, this time would be increased perhaps double if every phenomena
were completely investigated; but I have confined myself to the least
terms, and restrained, the limits of time as much as possible, without
contradicting facts and experiments.
This theory, perhaps, may be attacked by another objection, which it is
right to guard against. It may be told me that I have supposed, after
Newton, the heat of boiling water to be three times greater than that
of the sun in summer, and iron heated red-hot eight times greater than
boiling water, that is, 24 or 25 times greater than that of the actual
temperature of the earth, and that there is something hypothetical
in this supposition, on which I have founded the second basis of my
calculations, whose results would be, without doubt, very different if
this red heat of iron, or glass in incandescence, instead of being, in
fact, 25 times greater than the actual heat of the globe, were, for
example only 5 or 6 times as great.
The better to feel the force of this objection, let us make a
calculation of the refrigeration of the earth, upon the supposition
that in the time of incandescence it was only five times hotter than
it is according to our calculations; this solar heat, instead of a
compensation of 1/50 would have only made the compensation of 1/250 in
the time of incandescence, these two terms added together gives 6/250,
which multiplied by 2-1/2, the half of the sum of all the terms of the
diminution of heat, gives 15/250 for the total compensation which the
heat of the sun has made during the whole period of the deperdition
of the innate heat of the globe, which is 74047 years: therefore we
shall have : 15/250 :: 74047 : 888-14/25 from which we see that the
prolongation of refrigeration, which for a heat 28 times greater
than actual temperature, has been only 770 years, should have been
888-14/25 in the supposition that this first heat should have been only
five times greater than this actual temperature. This alone shews us
that if we even suppose this primitive heat below 25, there would only
be a longer prolongation of the refrigeration of the globe, and that
alone appears to me sufficient to satisfy the objection.
It may likewise be said, "you have calculated the duration of the
refrigeration of the planets, not only by the inverted ratio of their
diameters, but also by the inverted ratio of their density; this
might be well founded if we could imagine that in fact there exists
matter whose density is as different from that of our globe: but does
it exist? What, for example, will be the matter of which Saturn is
composed, since its density is more than five times less than that of
the earth?
To this I answer, that it would be very easy to find, in the vegetable
class, matters five or six times less dense than a mass of iron,
marble, hard calcareous stone, &c. of which we know that the earth is
principally composed; but without quiting the mineral kingdom, and
considering the density of these five matters, we have 21-10/72 for
iron, 8-25/72 for white marble, for gres 7-24/72, for common marble
and calcareous stone 7-20/72; taking the mean term of the densities
of these five matters, of which the terrestrial globe is principally
composed, we find its density to be 10-5/18. It is therefore required
to find a matter whose density is in the relation of 189 to 1000
density, which is the same as that between Saturn and the Earth. Now
this matter might be a kind of pumice stone, somewhat less dense than
common pumice stone, whose relative density is here 1-66/70; whence it
appears that Saturn is principally composed of a light matter similar
to pumice stone.
So likewise the density of the Earth being to that of Jupiter as 1000
to 292, we must suppose that Jupiter is composed of a more dense matter
than pumice stone, but much less dense than chalk.
The density of the Earth being to that of the Moon as 1000 to 702, this
secondary planet appears composed of a matter whose density is not
quite so great as that of hard calcareous stone, but more so than soft.
The density of the Earth being to that of Mars as 1000 to 730, this
planet must be composed of a matter somewhat more dense than that of
gres, and not so great as that of white marble.
But the density of the Earth being to that of Venus as 1000 to 12700,
it may be supposed that this planet is chiefly composed of a more
dense matter than emery, and less dense than zinc.
Finally, the density of the Earth being to that of Mercury :: 1000 :
2040, or :: 10-5/18 : 20,(966-2/3)/1000, it must be thought that this
planet is composed of a matter less dense than iron but more so than
tin.
To the question, how can animated nature, which you suppose every where
established, exist in planets of iron, emery, or pumice stone? I shall
answer, by the same causes, and by the same means as it exists on the
terrestrial globe, although composed of stone, gres, marble, iron, and
glass. There are other planets like our globe, whose principal is one
of these matters; but the external causes will soon have altered its
superficial strata, and according to the different degrees of heat or
cold, dryness or humidity, they will have converted this matter into a
fertile earth proper to receive the seeds of organized nature, which
only needs heat and moisture to develope itself.
Having answered the most obvious objections, it is necessary now to
explain the facts, and observations, by which we are assured that the
sun is only an accessory to the real heat, which continually emanates
from the globe of the earth; and it will be just, at the same time, to
see how comparable thermometers have taught us in a certain manner that
the heat in summer is equal in all the climates of the earth, excepting
Senegal, and some other parts of Africa, where the heat is greater than
elsewhere.
It may be incontestibly demonstrated, that the light, and consequently
the heat of the sun, emitted on the earth in the summer, is very great,
comparatively with that emitted by the same body in winter; and yet, by
very exact and reiterated observations, the difference of the real heat
of the sun in summer is very small. This alone would be sufficient to
prove that the heat of the sun makes only a small part of that of the
terrestrial globe; but in addition to this M. Amontons, by receiving
the rays of the sun on the same thermometer in summer and winter,
observed that the greatest heat in summer in our climate differs from
the cold in winter, when the water congeals, as only 7 differs from 6;
whereas it can be demonstrated that the action of the sun in summer is
about 66 times greater than that of the sun in winter; it therefore
cannot be doubted, that there is a fund of very great heat in the
terrestrial globe, on which, as a basis, the degrees of heat arise,
and that at the surface it does not give a greater quantity of heat
than that which comes from the sun.
If it be asked, how we can then assert that the heat in summer is 66
times grater than that in winter in our climate? I cannot give a better
answer than by referring to the memoirs given by the late M. de Mairan
in 1719, 1722, and 1765, and inserted in those of the Academy, where
he examines, with a scrupulous attention, the vicissitudes of summers
in different climates; the various causes for which may be reduced
to four principal ones: 1. The inclination under which the light of
the sun falls according to the different height of the sun on the
horizon; 2dly. The greater or less intensity of light in proportion
as its passage in the atmosphere is more or less oblique; 3dly. The
different distance of the earth to the sun in summer and winter; and
4thly. The inequalities of the length of days in different climates.
By the principle that heat is proportional to the action of light it
will be easily demonstrated, that these four united causes, combined
and compared, diminish with respect to our climate, this action of
the sun's heat in a ratio of about 66 to 1 between the summer and
the winter solstice; and this theoretical truth may be regarded as
certain, as the second truth from experience, and which demonstrates,
by the observations of the thermometer, immediately exposed to the
sun's rays in winter and summer, that the difference of real heat in
these two is, nevertheless, at most only from 7 to 6; I say at most,
for this determination given by M. Amontons is not nearly so exact as
that which has been made by M. de Mairan, who, after a great number
of final observations, proves that this relation is only as 32 to 31.
What, therefore, must indicate this prodigious inequality between
these two relations of the action of the _solar heat_, in summer and
winter, which is from 66 to 1; and of that of the _real heat_, which
is only from 32 to 31? Is it not evident that the innate heat of the
globe of the earth is considerably greater than that which comes to
us from the sun? It appears, in fact, that in the climate of Paris
this heat of the earth is 29 times greater in summer, and 491 times
greater in winter than that of the sun, as M. de Mairan has determined
it. But I have already said that we must not conclude, from these two
combined relations, the real one of the heat of the globe of the earth
to that which comes from the sun, and I have given reasons which have
determined me to suppose that we may estimate this heat of the sun 49
times less than the heat which emanates from the earth.
From the year 1701 to 1756 inclusive, a variety of observations were
made with thermometers, and the following were the results. The
greatest degree of heat, and of cold, which was experienced at Paris
in each year was collected; a total of these was made, and it was
found that the mean estimate, in all the thermometers, reduced to
Rheaumur's division, was 1026, for the greatest heat in summer, that
is 26 degrees above the freezing point; and that the mean degree of
cold in winter, during those 56 years, was 994, or 6 degrees below the
freezing point of water, whence we concluded that the greatest heat
in our summers at Paris differs from the greatest cold of our winters
only 1/32, since 994 : 1026 :: 31 : 32; and it was on this foundation
that we stated the latter to be the relation of the greatest heat to
the greatest cold. But it may be objected against the precision of
this valuation, the defect of the construction of the thermometer, and
Rheaumur's division (to which we have here reduced the scale of all the
rest); and this defect is extending only 1000 degrees below that of
ice, as if 1000 degrees were in fact, that of absolute cold, whereas
absolute cold does not exist in nature; and that of the smallest
heat should be supposed 10,000 instead of 1000, which would alter the
thermometer's gradation. It may likewise be said that it is possible
all our sensations between the greatest heat and the greatest cold are
comprised in as small an interval as that of a unit on 32 of heat, but
that the voice of judgment seems to be raised against this opinion,
and tells us this limit is too confined, and that it is much easier to
reduce this interval than to give it an eighth, or a seventh instead of
a thirty-second.
But be this valuation as it may, there can be no doubt of the truth
of these facts which we have drawn from our observations, for in the
same manner as we found, from the comparison of 56 successive years,
the heat of summer at Paris 1026, or 26 degrees above the freezing
point, we also found, with the same thermometers, that the heat in
summer was 1026 in every climate of the earth, from the equator to
the polar circle;[K] at Madagascar, in the islands of France and
Bourbon, Roderigo, Siam, and the East-Indies; at Algiers, Malta,
Cadiz, Montpelier, Lyons, Amsterdam, Upsal, Petersburgh, and as far
as Lapland, near the polar circle. At Cayenne, Peru, Martinico,
Carthagena in America; at Panama; in short, in all the climates of
the two hemispheres and continents where observations could be made,
it has been constantly found that the liquor of the thermometer rose
equally to 25, 26, or 27 degrees in the hottest days in summer; and
hence ensues the incontestible fact of the equality of heat in summer
in all climates of the earth. There are indeed some exceptions, for
at Senegal, and some few other places, the thermometer rises 5 or 6
degrees higher, to 31 or 32 degrees; but that arises from accidental
and local causes, which do not alter the truth of the observations,
nor the certainty of the general fact, which alone might demonstrate
to us, that there really exists a very great heat in the terrestrial
globe, that the effect, or the emanations, of which are nearly equal
in all the points of its surface, and that the sun, very far from
being the only sphere of heat which animates nature, is at best only
the regulator. This important fact, which we consign to posterity,
will enable it to discover the real progression of the diminution of
the heat of the terrestrial globe, which we have been only able to
determine in a hypothetical manner. In a few centuries, I am confident
it will be found that the greatest heat of summer, instead of raising
the liquor of the thermometer to 26, will not raise it to more than 25,
or 24; and from this effect, which is the result of all the combined
causes, a judgment may be formed of the value of each of the particular
causes, which produce the total effect of heat on the surface of
the globe; for the heat which belongs to the earth, and which it
has possessed from the time of incadescence, has very considerably
diminished, and will continue to diminish with the course of time: this
heat is independent of that which comes from the sun; the latter may
be looked upon as constant, and consequently in futurity will make a
greater compensation than at present. To the loss of this innate heat
of the globe there are two other particular causes, which may add a
considerable quantity of heat to the effect of the two first, the only
ones we have as yet taken notice of.
[K] See the Memoirs of Rheaumur in those of the Academy (year 1735 and
1741), and also of the Memoirs of M. de Mairan in those of the year
1765, p. 213.
One of these particular causes proceeds, in some measure, from the
first general cause, and may add something to it. It is certain that
during the time of incadescence, and indeed all the subsequent ages
till that of the refrigeration of the earth, not any of the volatile
matters could reside at the surface, or even in the internal part,
of the globe; they were raised and dispersed in the form of vapours,
and could not deposit themselves but successively in proportion as it
cooled, by which means some of these matters have penetrated through
the clefts and crevices of the earth to great depths, in an infinity of
places; and this is the primitive foundation of volcanos, which are all
found in lofty mountains, where the clefts of the earth are so much the
greater as these points of the globe are more projecting and isolated.
This deposit of the volatile combustible matters of the first ages
will have been greatly augmented by the addition of every combustible
matter which has been subsequently formed. Pyrites, sulphurs, coal,
bitumen, &c. have penetrated into the principal cavities of the earth,
and produced almost every where great masses of inflammable matters,
and often conflagrations, which have been manifested by earthquakes,
erruptions of volcanos, and by the hot springs which flow from
mountains, or run internally in the cavities of the earth. It may,
therefore, be presumed that these subterraneous fires, some of which
burn without explosion, and others with great noise and violence,
somewhat increase the general heat of the globe. Nevertheless this
addition of heat can be only very slight, for it has been observed
that it is nearly as cold on the top of volcanos as on the top of other
mountains of the same height, except at the very time when the volcano
throws out inflamed vapours or burning matters.
The second cause, which seems not to have been thought of, is the
motion of the moon round the earth. This secondary planet performs its
evolution round the earth in 27 days and one third, and being 85,325
leagues distance, it goes over a circumference of 536,329 leagues in
this space of time, which makes a motion of 817 leagues in an hour,
or from 13 to 14 leagues in a minute. Although this rout is, perhaps,
the slowest of all the celestial bodies, yet it is rapid enough to
produce on the earth, which serves for the axis or pivot to this
motion, a considerable heat by the friction which results from the
weight and velocity of this planet. But it is not possible to estimate
the quantity of heat produced by this exterior cause, because hitherto
we have had nothing which might serve us for a term of comparison. But
if we ever can discover the number, magnitude, and velocity, of all
the planets which circulate round the sun, we shall then be able to
judge of the quantity of heat which the moon can give to the earth, by
the much greater quantity of fire which all these vast bodies excite
in the sun. For my own part I am greatly inclined to think that the
heat produced by this cause in the globe of the earth, forms a very
considerable part of its own heat: and that, in consequence, we must
still extend the limits of time for the duration of nature. But let us
return to our principal object.
We have observed that the summers are very nearly equal in all climates
of the earth, and that this truth is founded on incontestible facts;
but it is not the same with respect to winters; they are very unequal,
and vary in different climates, as we remove further from that of the
equator, where the heat in winter and summer is nearly the same. I
think I have already explained in a satisfactory manner the cause of
this, viz, the suppression of the terrestrial heat. This suppression
is, as I have said, occasioned by the cold winds, which fall from the
air, bind the earth, freeze the waters, and shut up the emanations of
the terrestrial heat during the time the frosts remain; so that it is
not at all surprising that the cold in winter is in fact so much the
greater as we advance further towards the climates where the mass of
air, receiving the rays of the sun more obliquely is for that reason
colder.
But with respect to the cold as well as to the heat, there are some
countries which are an exception to the general rule. At Senegal,
Guinea, Angola, and probably in every country where the natives are
black, as in Nubia, the country of the Papous, New Guinea, &c. it
is certain that the heat is greater there than in any other part of
the earth; but this arises from local causes and therefore in those
particular climates where the east wind reigns during the whole year,
passes over a very considerable track of land, and receives a scorching
heat before it arrives to them, it is not surprising that the heat
is found 5, 6, and even 7 degrees greater than it is elsewhere. The
excessive colds of Siberia, are also to be attributed to that part of
the surface of the globe being much higher than that which surrounds
it. "The northern Asiatic countries (says the Baron Strahlenberg in
his description of the Russian Empire) are considerably more elevated
than the European. They are like a table, in comparison of the bed on
which they appear so be placed; for on coming from the west and leaving
Russia, we pass to the east by the mountains Ripha and Rymnikas to
enter Siberia, and constantly advance to an ascent." "There are many
places in Siberia," says M. Gmelin, "which are not less elevated above
the rest of the earth, nor less remote from its centre, than are many
high mountains in many other regions." These plains of Siberia, appear,
in fact, to be as high as the summit of the Riphean mountains, on
which the ice and snow do not wholly melt during summer; and if the
same effect do not happen in the plains of Siberia, it is because they
are less detached, for this local circumstance also adds much to the
duration and to the intensity of cold and heat. A vast plain once made
hot will retain its heat longer than a detached mountain, though both
are alike elevated; and for the same reason the mountain once cooled
will retain its snow or ice longer than the plain.
But if we compare the excess of heat with that of cold produced by
these particular and local causes, we shall be surprized to find, that
in Senegal, &c. where the heat is greatest, it never exceeds seven
degrees beyond the summer heat in other countries, which is 26 degrees
above the freezing point, while on the contrary, the colds of Siberia
sometimes reach 60 or 70 degrees below it, and that at Petersburgh,
Upsal, &c. under the same latitude as Siberia, the greatest cold is
not more than to 25 or 26 degrees below the freezing point; therefore,
we must conclude, that these local causes have much more influence in
cold than in hot climates. Although we cannot pretend to determine
what this great difference in the excess of cold and heat may produce,
yet by reflecting on it, it appears that we may easily conceive the
reason of this difference. The augmentation of the heat in such a
climate as Senegal can only proceed from the action of the air, the
nature of the soil, and the depression of the ground; for this country
being almost on a level with the sea, it is in a great measure covered
with scorching sands, over which an easterly wind continually blows;
this, instead of refreshing the air, only renders it more burning,
because it traverses over more than 2000 leagues of land in its way,
and consequently acquires a considerable degree of heat. But in
such countries as Siberia, where the plains are elevated like the
summits of mountains above the level of the rest of the earth, this
sole difference of elevation must produce an effect proportionally
greater than the depression of the ground of Senegal, which cannot be
supposed more than that of the level of the sea; for if the plains of
Siberia be only elevated 4 or 500 fathoms above the level of Upsal, or
Petersburgh, we must cease from being astonished that the excess of
cold is so great there; since the heat which emanates from the earth,
decreases at each point as the space increases, and this elevation of
the ground alone suffices to explain this great difference of cold
under the same latitude.
On this point there remains only one interesting question. Men,
animals, and plants, may, for some time, support the rigour of this
cold, which is 60 degrees below the freezing point; but could they also
support a heat which should be 60 degrees above it? To this we answer,
yes, provided we knew as well how to guard against the heat as we do
to shelter ourselves from the cold; and if the air could, during the
remainder of the year, refresh the earth, in the same manner as the
emanations of the heat of the globe warms the air in cold countries.
We know of plants, insects, and fish, which live and grow in baths of
45, 50, and even 60 degrees of heat; there are, therefore, species in
living nature which can support this degree of heat; and as the negroes
are in the human race those whom a strong heat the least incommodes,
might we not conclude, according to this hypothesis, that the earth
has continued to decline from its original heat, and that the race of
negroes are more ancient than that of white people?
_GENERAL VIEWS OF NATURE._