are produced by rains, floods, and torrents from the high lands. Their
origins proceed from the vapours which the sun raises above the surface
of the ocean, and which the wind transports through every climate. These
vapours, which are sustained in the air, and conveyed at the will of the
winds, are stopped in their progress by the tops of the hills which they
encounter, where they accumulate until they become clouds and fall in
the form of rain, dew, or snow. These waters at first descend upon the
plains without any fixed course, but by degrees hollow out a bed for
themselves; by their natural bent they run to the bottom of mountains,
and penetrating or dissolving the land easiest to divide, they carry
earth and sand away with them, cut deep channels in the plains, form
themselves into rivers, and open a passage into the sea, which
constantly receives as much water from the land rivers as it loses by
evaporation. The windings in the channels of rivers have sinuosities,
whose angles are correspondent to each other, so that where the waves
form a saliant angle on one side, the other has an exactly opposite one;
and as hills and mountains, which may be considered as the banks of the
vallies which separate them, have also sinuosities in corresponding
angles, it seems to demonstrate that the vallies have been formed, by
degrees, by the currents of the sea, in the same manner as the rivers
have hollowed out their beds on the earth.
The waters which run on the surface of the earth, and support its
verdure and fertility, are not perhaps one half of those which the
vapours produce; for there are many veins of water which sink to great
depths in the internal part of the earth. In some places we are certain
to meet with water by digging; in others, not any can be found. In
almost all vallies and low grounds water is certain to be met with at
moderate depths; but, on the contrary, in all high places it cannot be
extracted from the bowels of the earth, but must be collected from the
heavens. There are countries of great extent where a spring cannot be
found, and where all the water which supplies the inhabitants and
animals with drink is contained in pools and cisterns. In the east,
especially in Arabia, Egypt, and Persia, wells are extremely scarce, and
the people have been obliged to make reservoirs of a considerable extent
to collect the waters as it falls from the heavens. These works,
projected and executed from public necessity, are the most beautiful and
magnificent monuments of the eastern nations; some of the reservoirs
occupy a space of two square miles, and serve to fertilize whole
provinces, by means of baths and small rivulets that let it out on every
side. But in low countries, where the greatest rivers flow, we cannot
dig far from the surface, without meeting with water, and in fields
situate in the environs of rivers it is often obtained by a few strokes
with a pick-axe.
The water, found in such quantities in low grounds, comes principally
from the neighbouring hills and eminences; at the time of great rains or
sudden melting of snow, a part of the water flows on the surface, but
most of it penetrates through the small cracks and crevices it finds in
the earth and rocks. This water springs up again to the surface wherever
it can find vent; but it often filters through the sand until it comes
to a bottom of clay or solid earth, where it forms subterraneous lakes,
rivulets, and perhaps rivers, whose courses are entirely unknown; they
must, however, follow the general laws of nature, and constantly flow
from the higher grounds to the lower, and consequently these
subterraneous waters must, in the end, fall into the sea, or collect in
some low place, either on the surface or in the interior part of the
earth; for there are several lakes into which no rivers enter, nor from
which there are not any issue; and a much greater number, which do not
receive any considerable river, that are the sources of the greatest
rivers on earth; such as the lake of St. Laurence; the lake Chiamè,
from whence spring two great rivers that water the kingdoms of Asam and
Pegu; the lake of Assiniboil in America; those of Ozera in Muscovy, that
give rise to the river Irtis, and a great number of others. These lakes,
it is evident, must be produced by the waters from the high lands
passing through subterraneous passages, and collecting in the lowest
places. Some indeed have asserted that lakes are to be found on the
summit of the highest mountains; but to this no credit can be given, for
those found on the Alps, and other elevated places, are all surrounded
by much more lofty mountains, and derive their origin from the waters
which run down the sides, or are filtered through those eminences in the
same manner as the lakes in the plains obtain their sources from the
neighbouring hills which overtop them.
It is apparent, therefore, that lakes have existence in the bowels of
the earth, especially under large plains and extensive vallies.
Mountains, hills, and all eminences have either a perpendicular or
inclined situation, and are exposed on all sides; the waters which fall
on their summits, after having penetrated into the earth, cannot fail,
from the declivity of the ground, of finding issue in many places, and
breaking in forms out of springs and fountains, and consequently there
will be little, if any water, remain in the mountains. On the contrary,
in plains, as the water which filters through the earth can find no
vent, it must collect in subterraneous caverns, or be dispersed and
divided among sand and gravel. It is these waters which are so
universally diffused through low grounds. The bottom of a pit or well is
nothing else but a kind of bason into which the waters that issue from
the adjoining lands insinuate themselves, at first falling drop by drop,
but afterwards, as the passages are opened, it receives supplies from
greater distances, and then continually runs in little streams or rills;
from which circumstance, although we can find water in any part of a
plain, yet we can obtain a supply but for a certain number of wells,
proportionate to the quantity of water dispersed, or rather to the
extent of the higher lands from whence they come.
It is unnecessary to dig below the level of the river to find water; it
is generally met with at much less depths, and there is no appearance
that waters of rivers filter far through the earth. The origin of waters
found in the earth below the level of rivers is not to be attributed to
them; for in rivers or torrents which are dried up, or whose courses
have been turned, we find no greater quantity of water by digging in
their beds than in the neighbouring lands at an equal depth.
A piece of land of five or six feet in thickness is sufficient to
contain water, and prevent it from escaping; and I have often observed
that the banks of brooks and pools are not sensibly wet at six inches
distance from the water.
It is true that the extent of the filtration is in proportion as the
soil is more or less penetrable; but if we examine the standing pools
with sandy bottoms, we shall perceive the water confined in the small
compass it had hollowed itself, and the moisture spread but a very few
inches; even in vegetable earth it has no great extent, which must be
more porous than sand or hard soil. It is a certain fact, that in a
garden we may almost inundate one bed without those nearly adjoining
feeling any moisture from it[65:A]. I have examined pieces of garden
ground, eight or ten feet thick, which had not been stirred for many
years, and whose surface was nearly level, and found that the rain water
never penetrated deeper than three or four feet; and on turning it up in
the spring, after a wet winter, I found it as dry as when first heaped
together.
I made the same observation on earth which had laid in ridges two
hundred years; below three or four feet it was as dry as dust; from
which it is plain that water does not extend so far by filtration as has
been generally imagined.
By this means, therefore, the internal part of the earth can be supplied
with a very small part; but water by its own weight descends from the
surface to the greatest depths; it sinks through natural conduits, or
penetrates small passages for itself; it follows the roots of trees, the
cracks in rocks, the interstices in the earth, and divides and extends
on all sides into an infinity of small branches and rills, always
descending until its passage is opposed by clay or some solid body,
where it continues collecting, and at length breaks out in form of
springs upon the surface.
It would be very difficult to make an exact calculation of the quantity
of subterraneous waters which have no apparent vent. Many have pretended
that it greatly surpasses all the waters that are on the surface of the
earth.
Without mentioning those who have advanced that the interior part of the
globe is entirely filled with water, there are some who believe there
are an infinity of floods, rivulets, and lakes in the bowels of the
earth. But this opinion does not seem to be properly founded, and it is
more probable that the quantity of subterraneous water, which never
appears on the surface, is not very considerable; for if these
subterraneous rivers are so very numerous, why do we never see any of
their mouths forcing their way through the surface? Besides, rivers, and
all running waters, produce great alterations on the surface of the
earth; they transport the soil, wear away the most solid rocks, and
displace all matters which oppose their passage. It would certainly be
the same in subterraneous rivers; the same effects would be produced;
but no such alterations have ever as yet been observed; the different
strata remains parallel, and every where preserves its original
position; and it is but in a very few places that any considerable
subterraneous veins of water have been discovered. Thus water in the
internal part of the earth, though great, acts but in a small degree, as
it is divided in an infinity of little streams, and retained by a number
of obstacles; and being so generally dispersed, it gives rise to many
substances totally different from primitive matters, both in form and
organization.
From all these observations we may fairly conclude, that it is the
continual motion of the flux and reflux of the sea which has produced
mountains, vallies, and other inequalities on the surface of the earth;
that it is the currents of the ocean which have hollowed vallies, raised
hills, and given them corresponding directions; that it is those waters
of the sea which, by transporting earth, &c. and depositing them in
horizontal layers, have formed the parallel strata; that it is the
waters from heaven, which by degrees destroy the effects of the sea, by
continually lowering the summit of mountains, filling up vallies, and
stopping the mouths of gulphs and rivers, and which, by bringing all to
a level, will, in the course of time, return this earth to the sea,
which, by its natural operations, will again form new continents,
containing vallies and mountains exactly similar to those which we at
present inhabit.
FOOTNOTES:
[25:A] Particularly Scotland and Ireland.
[65:A] These facts are so easily demonstrated, that the smallest
observation will prove their veracity.
PROOF
OF
_THE THEORY OF THE EARTH_.
ARTICLE I.
ON THE FORMATION OF THE PLANETS.
Our subject being Natural History, we would willingly dispense with
astronomical observations; but as the nature of the earth is so closely
connected with the heavenly bodies, and such observations being
calculated to illustrate more fully what has been said, it is necessary
to give some general ideas of the formation, motion, figure of the earth
and other planets.
The earth is a globe of about three thousand leagues diameter; it is
situate one thousand millions of leagues from the sun, around which it
makes its revolution in three hundred and sixty-five days. This
revolution is the result of two forces; the one may be considered as an
impulse from right to left, or from left to right, and the other an
attraction from above downwards, or beneath upwards, to a common centre.
The direction of these two forces, and their quantities, are so nicely
combined and proportioned, that they produce an almost uniform motion in
an ellipse, very near to a circle. Like the other planets the earth is
opaque, it throws out a shadow; it receives and reflects the light of
the sun, round which it revolves in a space of time proportioned to its
relative distance and density. It also turns round its own axis once in
twenty-four hours, and its axis is inclined 66-1/4 degrees on the plane
of the orbit. Its figure is spheroidical, the two axes of which differ
about 160th part from each other, and the smallest axis is that round
which the revolution is made.
These are the principal phenomena of the earth, the result of
discoveries made by means of geometry, astronomy, and navigation. We
shall not here enter into the detail of the proofs and observations by
which those facts have been ascertained, but only make a few remarks to
clear up what is still doubtful, and at the same time give our ideas
respecting the formation of the planets, and the different changes thro'
which it is possible they have passed before they arrived at the state
we at present see them.
There have been so many systems and hypotheses framed upon the formation
of the terrestrial globe, and the changes which it has undergone, that
we may presume to add our conjectures to those who have written upon the
subject, especially as we mean to support them with a greater degree of
probability than has hitherto been done: and we are the more inclined to
deliver our opinion upon this subject, from the hope that we shall
enable the reader to pronounce on the difference between an hypothesis
drawn from possibilities, and a theory founded in facts; between a
system, such as we are here about to present, on the formation and
original state of the earth, and a physical history of its real
condition, which has been given in the preceding discourse.
Galileo having found the laws of falling bodies, and Kepler having
observed that the area described by the principal planets in moving
round the sun, and those of the satellites round the planets to which
they belong, are proportionable to the time of their revolutions, and
that such periods were also in proportion to the square roots of the
cubes of their distances from the sun, or principal planets. Newton
found that the force which caused heavy bodies to fall on the surface of
the earth, extended to the moon, and retained it in its orbit; that this
force diminished in the same proportion as the square of the distance
increased, and consequently that the moon is attracted by the earth;
that the earth and planets are attracted by the sun; and that in general
all bodies which revolve round a centre, and describe areas proportioned
to the times of their revolution, are attracted towards that point. This
power, known by the name of GRAVITY, is therefore diffused throughout
all matter; planets, comets, the sun, the earth, and all nature, is
subject to its laws, and it serves as a basis to the general harmony
which reigns in the universe. Nothing is better proved in physics than
the actual existence of this power in every material substance.
Observation has confirmed the effects of this power, and geometrical
calculations have determined the quantity and relations of it.
This general cause being known, the effects would easily be deduced from
it, if the action of the powers which produce it were not too
complicated. A single moment's reflection upon the solar system will
fully demonstrate the difficulties that have attended this subject; the
principal planets are attracted by the sun, and the sun by the planets;
the satellites are also attracted by their principal planets, and each
planet attracts all the rest, and is attracted by them. All these
actions and reactions vary according to the quantities of matter and the
distances, and produce great inequalities and irregularities. How is so
great a number of connections to be combined and estimated? It appears
almost impossible in such a crowd of objects to follow any particular
one; nevertheless those difficulties have been surmounted, and
calculation has confirmed the suppositions of them, each observation is
become a new demonstration, and the systematic order of the universe is
laid open to the eyes of all those who can distinguish truth from error.
We feel some little stop, by the force of impulsion remaining unknown;
but this, however, does not by any means affect the general theory. We
evidently see the force of attraction always draws the planets towards
the sun, they would fall in a perpendicular line, on that planet, if
they were not repelled by some other power that obliges them to move in
a straight line, and which impulsive force would compel them to fly off
the tangents of their respective orbits, if the force of attraction
ceased one moment. The force of impulsion was certainly communicated to
the planets by the hand of the Almighty, when he gave motion to the
universe; but we ought as much as possible to abstain in physics from
having recourse to supernatural causes; and it appears that a probable
reason may be given for this impulsive force, perfectly accordant with
the law of mechanics, and not by any means more astonishing than the
changes and revolutions which may and must happen in the universe.
The sphere of the sun's attraction does not confine itself to the orbs
of the planets, but extends to a remote distance, always decreasing in
the same ratio as the square of the distance increases; it is
demonstrated that the comets which are lost to our sight, in the regions
of the sky, obey this power, and by it their motions, like that of the
planets, are regulated. All these stars, whose tracts are so different,
move round the sun, and describe areas proportioned to the time; the
planets in ellipses more or less approaching a circle, and the comets in
narrow ellipses of a great extent. Comets and planets move, therefore,
by virtue of the force of attraction and impulsion, which continually
acting at one time obliges them to describe these courses; but it must
be remarked that comets pass over the solar system in all directions,
and that the inclinations of their orbits are very different, insomuch
that, although subject like the planets to the force of attraction, they
have nothing in common with respect to their progressive or impulsive
motions, but appear in this respect independent of each other: the
planets, on the contrary, move round the sun in the same direction, and
almost in the same plane, never exceeding 7-1/2 degrees of inclination
in their planes, the most distant from their orbits. This conformity of
position and direction in the motion of the planets, necessarily implies
that their impulsive force has been communicated to them by one and the
same cause.
May it not be imagined, with some degree of probability, that a comet
falling into the body of the sun, will displace and separate some parts
from the surface, and communicate to them a motion of impulsion,
insomuch that the planets may formerly have belonged to the body of the
sun, and been detached therefrom by an impulsive force, and which they
still preserve.
This supposition appears to be at least as well founded as the opinion
of Leibnitz, who supposes that the earth and planets had formerly been
suns; and his system, of which an account will be given in the fifth
article, would have been more comprehensive and more agreeable to
probability, if he had raised himself to this idea. We agree with him in
thinking that this effect was produced at the time when Moses said that
God divided light from darkness; for, according to Leibnitz, light was
divided from darkness when the planets were extinguished; but in our
supposition there was a real physical separation, since the opaque
bodies of the planets were divided from the luminous matter which
composes the sun.
This idea of the cause of the impulsive force of the planets will be
found much less objectionable, when an estimation is made of the
analogies and degrees of probability, by which it may be supported. In
the first place, the motion of the planets are in the same direction,
from West to East, and therefore, according to calculation, it is
sixty-four to one that such would not have been the case, if they had
not been indebted to the same cause for their impulsive forces.
This, probably, will be considerably augmented by the second analogy,
viz. that the inclination of the planes of the orbits do not exceed
7-1/2 degrees; for, by comparing the spaces, we shall find there is
twenty-four to one, that two planets are found in their most distant
places at the same time, and consequently ⁵, or 7,692,624 to one,
that all six would by chance be thus placed; or, what amounts to the
same, there is a great degree of probability that the planets have been
impressed with one common moving force, and which has given them this
position. But what can have bestowed this common impulsive motion, but
the force and direction of the bodies by which it was originally
communicated? It may therefore be concluded, with great probability,
that the planets received their impulsive motion by one single stroke.
This likelihood, which is almost equivalent to a certainty, being
established, I seek to know what moving bodies could produce this
effect, and I find nothing but comets capable of communicating a motion
to such vast bodies.
By examining the course of comets, we shall be easily persuaded, that it
is almost necessary for some of them occasionally to fall into the sun.
That of 1680 approached so near, that at its perihelium it was not more
distant from the sun than a sixteenth part of its diameter, and if it
returns, as there is every appearance it will, in 2255, it may then
possibly fall into the sun; that must depend on the rencounters it will
meet with in its road, and of the retardment it suffers in passing
through the atmosphere of the sun[78:A].
We may, therefore, presume with the great Newton, that comets sometimes
fall into the sun; but this fall may be made in different directions. If
they fall perpendicular, or in a direction not very oblique, they will
remain in the sun, and serve for food to the fire which that luminary
consumes, and the motion of impulsion which they will have communicated
to the sun, will produce no other effect than that of removing it more
or less, according as the mass of the comet will be more or less
considerable; but if the fall of the comet is in a very oblique
direction, which will most frequently happen, then the comet will only
graze the surface of the sun, or slightly furrow it; and in this case it
may drive out some parts of matter to which it will communicate a common
motion of impulsion, and these parts so forced out of the body of the
sun, and even the comet itself, may then become planets, and turn round
this luminary in the same direction, and in almost the same plane. We
might perhaps calculate what quantity of matter, velocity, and direction
a comet should have, to impel from the sun an equal quantity of matter
to that which the six planets and their satellites contain; but it will
be sufficient to observe here, that all the planets, with their
satellites, do not make the 650th part of the mass of the sun,[79:A]
because the density of the large planets, Saturn and Jupiter, is less
than that of the sun; and although the earth be four times, and the moon
near five times more dense than the sun, they are nevertheless but as
atoms in comparison with his extensive body.