under the calcareous rock in Derbyshire. I only remarked, that at
the lowest part of that rocky mountain which was in sight, there
were oyster shells mixed in the stone; and part of the high county
of Derby being probably as much above the level of the sea, as the
coal mines of Whitehaven were below it, seemed a proof, that there
had been a great _bouleversement_ in the surface of that island, some
part of it having been depressed under the sea, and other parts,
which had been under it, being raised above it. Such changes in the
superficial parts of the globe, seemed to me unlikely to happen,
if the earth were solid to the centre. I therefore imagined, that
the internal parts might be a fluid more dense, and of greater
specific gravity than any of the solids we are acquainted with, which
therefore might swim in or upon that fluid. Thus the surface of the
globe would be a shell, capable of being broken and disordered by
the violent movements of the fluid on which it rested. And as air
has been compressed by art so as to be twice as dense as water, in
which case, if such air and water could be contained in a strong
glass vessel, the air would be seen to take the lowest place, and
the water to float above and upon it; and as we know not yet the
degree of density to which air may be compressed, and M. Amontons
calculated, that its density increasing as it approached the centre,
in the same proportion as above the surface, it would at the depth of
[___] leagues, be heavier than gold, possibly the dense fluid occupying
the internal parts of the globe might be air compressed. And as the
force of expansion in dense air when heated is in proportion to its
density, this central air might afford another agent to move the
surface, as well as be of use in keeping alive the subterraneous
fires; though, as you observe, the sudden rarefaction of water coming
into contact without those fires, may also be an agent sufficiently
strong for that purpose, when acting between the incumbent earth and
the fluid on which it rests.
If one might indulge imagination in supposing how such a globe
was formed, I should conceive, that all the elements in separate
particles being originally mixed in confusion, and occupying a great
space, they would (as soon as the almighty fiat ordained gravity,
or the mutual attraction of certain parts, and the mutual repulsion
of others, to exist) all move to their common centre: that the air
being a fluid whose parts repel each other, though drawn to the
common centre by their gravity, would be densest towards the centre,
and rarer as more remote; consequently all matters lighter than the
central parts of that air, and immersed in it, would recede from
the centre, and rise till they arrived at that region of the air
which was of the same specific gravity with themselves, where they
would rest; while other matter, mixed with the lighter air, would
descend, and the two meeting would form the shell of the first earth,
leaving the upper atmosphere nearly clear. The original movement of
the parts towards their common centre would naturally form a whirl
there; which would continue upon the turning of the new-formed globe
upon its axis, and the greatest diameter of the shell would be in its
equator. If by any accident afterwards the axis should be changed,
the dense internal fluid, by altering its form, must burst the shell,
and throw all its substance into the confusion in which we find it. I
will not trouble you at present with my fancies concerning the manner
of forming the rest of our system. Superior beings smile at our
theories, and at our presumption in making them. I will just mention,
that your observation of the ferruginous nature of the lava which is
thrown out from the depths of our volcanoes, gave me great pleasure.
It has long been a supposition of mine, that the iron contained in
the surface of the globe has made it capable of becoming, as it is,
a great magnet; that the fluid of magnetism perhaps exists in all
space; so that there is a magnetical north and south of the universe,
as well as of this globe, and that if it were possible for a man to
fly from star to star, he might govern his course by the compass;
that it was by the power of this general magnetism this globe became
a particular magnet. In soft or hot iron the fluid of magnetism is
naturally diffused equally; when within the influence of the magnet
it is drawn to one end of the iron, made denser there and rarer
at the other. While the iron continues soft and hot, it is only a
temporary magnet; if it cools or grows hard in that situation, it
becomes a permanent one, the magnetic fluid not easily resuming its
equilibrium. Perhaps it may be owing to the permanent magnetism of
this globe, which it had not at first, that its axis is at present
kept parallel to itself, and not liable to the changes it formerly
suffered, which occasioned the rupture of its shell, the submersions
and emersions of its lands and the confusion of its seasons. The
present polar and equatorial diameters differing from each other
near ten leagues, it is easy to conceive, in case some power should
shift the axis gradually, and place it in the present equator, and
make the new equator pass through the present poles, what a sinking
of the waters would happen in the present equatorial regions, and
what a rising in the present polar regions; so that vast tracts would
be discovered, that now are under water, and others covered, that
are now dry, the water rising and sinking in the different extremes
near five leagues. Such an operation as this possibly occasioned
much of Europe, and among the rest this Mountain of Passy on which I
live, and which is composed of limestone, rock and sea-shells, to be
abandoned by the sea, and to change its ancient climate, which seems
to have been a hot one. The globe being now become a perfect magnet,
we are, perhaps, safe from any change of its axis. But we are still
subject to the accidents on the surface, which are occasioned by a
wave in the internal ponderous fluid; and such a wave is producible
by the sudden violent explosion you mention, happening from the
junction of water and fire under the earth, which not only lifts
the incumbent earth that is over the explosion, but impressing with
the same force the fluid under it, creates a wave, that may run a
thousand leagues, lifting, and thereby shaking, successively, all
the countries under which it passes. I know not, whether I have
expressed myself so clearly, as not to get out of your sight in
these reveries. It they occasion any new enquiries, and produce a
better hypothesis, they will not be quite useless. You see I have
given a loose to imagination; but I approve much more your method
of philosophising, which proceeds upon actual observation, makes
a collection of facts, and concludes no farther than those facts
will warrant. In my present circumstances, that mode of studying
the nature of the globe is out of my power, and therefore I have
permitted myself to wander a little in the wilds of fancy. With great
esteem,
I have the honour to be, Sir, &c.
BENJ. FRANKLIN.
_P. S._ I have heard, that chymists can by their art decompose stone
and wood, extracting a considerable quantity of water from the one,
and air from the other. It seems natural to conclude from this, that
water and air were ingredients in their original composition: for
men cannot make new matter of any kind. In the same manner may we
not suppose, that when we consume combustibles of all kinds, and
produce heat or light, we do not create that heat or light; but only
decompose a substance, which received it originally as a part of its
composition? Heat may be thus considered as originally in a fluid
state; but, attracted by organized bodies in their growth, becomes a
part of the solid. Besides this, I can conceive, that in the first
assemblage of the particles of which this earth is composed, each
brought its portion of the loose heat that had been connected with
it, and the whole, when pressed together, produced the internal fire
that still subsists.
FOOTNOTE:
[21] In an American periodical publication, this paper is said to
have been so endorsed in Dr. Franklin's hand. We extract the paper
itself, from the Transactions of the American Philosophical Society,
where it was read Nov. 21, 1788. The two papers that follow it are
from the same work, and were read in the Society the preceding day,
and the other Jan. 15, 1790. _Editor._
TO DAVID RITTENHOUSE, ESQ.
_New and curious Theory of Light and Heat._
[No date.]
Universal space, as far as we know of it, seems to be filled with a
subtle fluid, whose motion, or vibration, is called light.
This fluid may possibly be the same with that, which, being attracted
by, and entering into other more solid matter, dilates the substance
by separating the constituent particles, and so rendering some solids
fluid, and maintaining the fluidity of others; of which fluid, when
our bodies are totally deprived, they are said to be frozen; when
they have a proper quantity, they are in health, and fit to perform
all their functions; it is then called natural heat; when too much,
it is called fever; and when forced into the body in too great a
quantity from without, it gives pain, by separating and destroying
the flesh, and is then called burning, and the fluid so entering and
acting is called fire.
While organised bodies, animal or vegetable, are augmenting in
growth, or are supplying their continual waste, is not this done by
attracting and consolidating this fluid called fire, so as to form
of it a part of their substance? And is it not a separation of the
parts of such substance, which, dissolving its solid state, sets that
subtle fluid at liberty, when it again makes its appearance as fire?
For the power of man relative to matter, seems limited to the
separating or mixing the various kinds of it, or changing its form
and appearance by different compositions of it; but does not extend
to the making or creating new matter, or annihilating the old. Thus,
if fire be an original element or kind of matter, its quantity is
fixed and permanent in the universe. We cannot destroy any part of
it, or make addition to it; we can only separate it from that which
confines it, and so set it at liberty; as when we put wood in a
situation to be burnt, or transfer it from one solid to another, as
when we make lime by burning stone, a part of the fire dislodged
in the fuel being left in the stone. May not this fluid, when at
liberty, be capable of penetrating and entering into all bodies,
organised or not, quitting easily in totality those not organised,
and quitting easily in part those which are; the part assumed and
fixed remaining till the body is dissolved?
Is it not this fluid which keeps asunder the particles of air,
permitting them to approach, or separating them more, in proportion
as its quantity is diminished or augmented?
Is it not the greater gravity of the particles of air, which forces
the particles of this fluid to mount with the matters to which it is
attached, as smoke or vapour?
Does it not seem to have a greater affinity with water, since it will
quit a solid to unite with that fluid, and go off with it in vapour,
leaving the solid cold to the touch, and the degree measurable by the
thermometer?
The vapour rises attached to this fluid, but at a certain height they
separate, and the vapour descends in rain, retaining but little of
it, in snow or hail less. What becomes of that fluid? Does it rise
above our atmosphere, and mix with the universal mass of the same
kind?
Or does a spherical stratum of it, denser, as less mixed with air,
attracted by this globe, and repelled or pushed up only to a certain
height from its surface, by the greater weight of air, remain there
surrounding the globe, and proceeding with it round the sun?
In such case, as there may be a continuity or communication of this
fluid through the air quite down to the earth, is it not by the
vibrations given to it, by the sun, that light appears to us? And
may it not be, that every one of the infinitely small vibrations,
striking common matter with a certain force, enters its substance,
is held there by attraction, and augmented by succeeding vibrations,
till the matter has received as much as their force can drive into it?
Is it not thus, that the surface of this globe is continually heated
by such repeated vibrations in the day, and cooled by the escape of
the heat when those vibrations are discontinued in the night, or
intercepted and reflected by clouds?
Is it not thus, that fire is amassed and makes the greatest part of
the substance of combustible bodies?
Perhaps, when this globe was first formed, and its original particles
took their place at certain distances from the centre, in proportion
to their greater or less gravity, the fluid fire, attracted towards
that centre, might in great part be obliged, as lightest, to take
place above the rest, and thus form the sphere of fire above
supposed, which would afterwards be continually diminishing by the
substance it afforded to organised bodies, and the quantity restored
to it again, by the burning or other separating of the parts of those
bodies.
Is not the natural heat of animals thus produced, by separating in
digestion the parts of food, and setting their fire at liberty?
Is it not this sphere of fire which kindles the wandering globes that
sometimes pass through it in our course round the sun, have their
surface kindled by it, and burst when their included air is greatly
rarefied by the heat on their burning surfaces?
May it not have been from such considerations that the ancient
philosophers supposed a sphere of fire to exist above the air of our
atmosphere?
B. FRANKLIN.
TO MR. BODOIN.
_Queries and Conjectures relating to Magnetism and the Theory of
the Earth._
[No date.]
DEAR SIR,
I received your favours by Messrs. Gore, Hilliard, and Lee, with
whose conversation I was much pleased, and wished for more of it; but
their stay with us was too short. Whenever you recommend any of your
friends to me, you oblige me.
I want to know whether your Philosophical Society received the
second volume of our Transactions. I sent it, but never heard of its
arriving. If it miscarried, I will send another. Has your Society
among its books the French work _Sur les Arts, et les Metiers_? It
is voluminous, well executed, and may be useful in our country. I
have bequeathed it them in my will; but if they have it already, I
will substitute something else.
Our ancient correspondence used to have something philosophical in
it. As you are now more free from public cares, and I expect to be so
in a few months, why may we not resume that kind of correspondence?
Our much regretted friend Winthrop once made me the compliment, that
I was good at starting game for philosophers, let me try if I can
start a little for you.
Has the question, how came the earth by its magnetism, ever been
considered?
Is it likely that _iron ore_ immediately existed when this globe was
first formed; or may it not rather be supposed a gradual production
of time?
If the earth is at present magnetical, in virtue of the masses of
iron ore contained in it, might not some ages pass before it had
magnetic polarity?
Since iron ore may exist without that polarity, and by being placed
in certain circumstances may obtain it, from an external cause, is
it not possible that the earth received its magnetism from some such
cause?
In short, may not a magnetic power exist throughout our system,
perhaps through all systems, so that if men could make a voyage in
the starry regions, a compass might be of use? And may not such
universal magnetism, with its uniform direction, be serviceable in
keeping the diurnal revolution of a planet more steady to the same
axis?
Lastly, as the poles of magnets may be changed by the presence of
stronger magnets, might not, in ancient times, the near passing of
some large comet of greater magnetic power than this globe of ours
have been a means of changing its poles, and thereby wrecking and
deranging its surface, placing in different regions the effect of
centrifugal force, so as to raise the waters of the sea in some,
while they were depressed in others?
Let me add another question or two, not relating indeed to magnetism,
but, however, to the theory of the earth.
Is not the finding of great quantities of shells and bones of animals
(natural to hot climates) in the cold ones of our present world,
some proof that its poles have been changed? Is not the supposition
that the poles have been changed, the easiest way of accounting for
the deluge, by getting rid of the old difficulty how to dispose of
its waters after it was over? Since if the poles were again to be
changed, and placed in the present equator, the sea would fall there
about fifteen miles in height, and rise as much in the present polar
regions; and the effect would be proportionable if the new poles were
placed any where between the present and the equator.
Does not the apparent wreck of the surface of this globe, thrown up
into long ridges of mountains, with strata in various positions, make
it probable, that its internal mass is a fluid; but a fluid so dense
as to float the heaviest of our substances? Do we know the limit of
condensation air is capable of? Supposing it to grow denser _within_
the surface, in the same proportion nearly as it does _without_, at
what depth may it be equal in density with gold?
Can we easily conceive how the strata of the earth could have been
so deranged, if it had not been a mere shell supported by a heavier
fluid? Would not such a supposed internal fluid globe be immediately
sensible of a change in the situation of the earth's axis, alter its
form, and thereby burst the shell, and throw up parts of it above
the rest? As, if we would alter the position of the fluid contained
in the shell of an egg, and place its longest diameter where the
shortest now is, the shell must break; but would be much harder to
break; if the whole internal substance were as solid and hard as the
shell.
Might not a wave, by any means raised in this supposed internal ocean
of extremely dense fluid, raise in some degree, as it passes, the
present shell of incumbent earth, and break it in some places, as in
earthquakes? And may not the progress of such wave, and the disorders
it occasions among the solids of the shell, account for the rumbling
sound being first heard at a distance, augmenting as it approaches,
and gradually dying away as it proceeds? A circumstance observed by
the inhabitants of South America in their last great earthquake, that
noise coming from a place, some degrees north of Lima, and being
traced by enquiry quite down to Buenos Ayres, proceeded regularly
from north to south at the rate of [___] leagues per minute, as I was
informed by a very ingenious Peruvian whom I met with at Paris.
B. FRANKLIN.
TO M. DUBOURG.
_On the Nature of Sea Coal[22]._
**** I am persuaded, as well as you, that the sea coal has a
vegetable origin, and that it has been formed near the surface of
the earth; but as preceding convulsions of nature had served to bring
it very deep in many places, and covered it with many different
strata, we are indebted to subsequent convulsions for having brought
within our view the extremities of its veins, so as to lead us to
penetrate the earth in search of it. I visited last summer a large
coal-mine at Whitehaven, in Cumberland; and in following the vein
and descending by degrees towards the sea, I penetrated below the
ocean, where the level of its surface was more than eight hundred
fathom above my head, and the miners assured me, that their works
extended some miles beyond the place where I then was, continually
and gradually descending under the sea. The slate, which forms the
roof of this coal mine, is impressed in many places with the figures
of leaves and branches of fern, which undoubtedly grew at the surface
when the slate was in the state of sand on the banks of the sea.
Thus it appears that this vein of coal has suffered a prodigious
settlement. ****
B. FRANKLIN.
FOOTNOTE:
[22] Retranslated from the French edition of Dr. Franklin's works.
_Editor._
TO DR. PRIESTLEY[23].
_Effect of Vegetation on noxious Air._
**** That the vegetable creation should restore the air which is
spoiled by the animal part of it, looks like a rational system, and
seems to be of a piece with the rest. Thus fire purifies water all
the world over. It purifies it by distillation, when it raises it in
vapours, and lets it fall in rain; and farther still by filtration,
when, keeping it fluid, it suffers that rain to percolate the
earth. We knew before, that putrid animal substances were converted
into sweet vegetables, when mixed with the earth, and applied as
manure; and now, it seems, that the same putrid substances, mixed
with the air, have a similar effect. The strong thriving state of
your mint, in putrid air, seems to shew, that the air is mended
by taking something from it, and not by adding to it. I hope this
will give some check to the rage of destroying trees that grow near
houses, which has accompanied our late improvements in gardening,
from an opinion of their being unwholesome. I am certain, from long
observation, that there is nothing unhealthy in the air of woods; for
we Americans have every where our country habitations in the midst
of woods, and no people on earth enjoy better health, or are more
prolific. ****
B. FRANKLIN.
FOOTNOTE:
[23] This extract is taken from Dr. Priestley's Experiments on
Air, Vol. I. page 94. It was written in answer to a note from Dr.
Priestley, informing our author of the result of certain experiments
on some plants which he had seen at Dr. Priestley's house in a very
flourishing state, in jars of highly noxious air. _Editor._
TO THE SAME[24].
_On the Inflammability of the Surface of certain Rivers in America._
_Craven-street, April 10, 1774._
DEAR SIR,
In compliance with your request, I have endeavoured to recollect the
circumstances of the American experiments I formerly mentioned to
you, of raising a flame on the surface of some waters there.
When I passed through New Jersey in 1764, I heard it several times
mentioned, that by applying a lighted candle near the surface of
some of their rivers, a sudden flame would catch and spread on the
water, continuing to burn for near half a minute. But the accounts I
received were so imperfect, that I could form no guess at the cause
of such an effect, and rather doubted the truth of it. I had no
opportunity of seeing the experiment; but calling to see a friend who
happened to be just returning home from making it himself, I learned
from him the manner of it; which was to choose a shallow place,
where the bottom could be reached by a walking-stick, and was muddy;
the mud was first to be stirred with the stick, and when a number
of small bubbles began to arise from it, the candle was applied.
The flame was so sudden and so strong, that it catched his ruffle
and spoiled it, as I saw. New Jersey having many pine-trees in many
parts of it, I then imagined that something like a volatile oil of
turpentine might be mixed with the waters from a pine-swamp, but this
supposition did not quite satisfy me. I mentioned the fact to some
philosophical friends on my return to England, but it was not much
attended to. I suppose I was thought a little too credulous.
In 1765, the Reverend Dr. Chandler received a letter from Dr.
Finley, President of the College in that province, relating the
same experiment. It was read at the Royal Society, November 21 of
that year, but not printed in the Transactions; perhaps because
it was thought too strange to be true, and some ridicule might be
apprehended, if any member should attempt to repeat it, in order to
ascertain, or refute it. The following is a copy of that account.
"A worthy gentleman, who lives at a few miles distance, informed
me, that in a certain small cove of a mill-pond, near his house, he
was surprized to see the surface of the water blaze like inflamed
spirits. I soon after went to the place, and made the experiment with
the same success. The bottom of the creek was muddy, and when stirred
up, so as to cause a considerable curl on the surface, and a lighted
candle held within two or three inches of it, the whole surface was
in a blaze, as instantly as the vapour of warm inflammable spirits,
and continued, when strongly agitated, for the space of several
seconds. It was at first imagined to be peculiar to that place; but
upon trial it was soon found, that such a bottom in other places
exhibited the same phenomenon. The discovery was accidentally made by
one belonging to the mill."
I have tried the experiment twice here in England, but without
success. The first was in a slow running water with a muddy bottom.
The second in a stagnant water at the bottom of a deep ditch. Being
some time employed in stirring this water, I ascribed an intermitting
fever, which seized me a few days after, to my breathing too much of
that foul air, which I stirred up from the bottom, and which I could
not avoid while I stooped, endeavouring to kindle it. The discoveries
you have lately made, of the manner in which inflammable air is in
some cases produced, may throw light on this experiment, and explain
its succeeding in some cases, and not in others. With the highest
esteem and respect,
I am, dear Sir, your most obedient humble servant,
B. FRANKLIN.
FOOTNOTE:
[24] From his Experiments on Air, Vol. I. page 321. _Editor._
TO DR. PERCIVAL[25].
_On the different Quantities of Rain which fall at different
Heights over the same Ground._
[No date.]