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I suspect some mistake creeps in by the au- is the same thing as giving it 1ƒ; (i. e. if thor's not distinguishing between a great force force applied to matter at rest, can put it in applied at once, or a small one continually ap-motion, and give it equal force) where then plied to a mass of matter, in order to move it. I is vis inertia? If it existed at all in matter, think it is generally allowed by the philoso- should we not find the quantity of its resistphers, and, for aught we know, is certainly ance subtracted from the force given? true, that there is no mass of matter, how great In No. 4. our author goes on and says, "the soever, but may be moved by any force how body a requires a certain force to be impressed small soever, (taking friction out of the ques-on it to be moved with a celerity as c, or such tion) and this small force continued, will in a force is necessary; and therefore makes a time bring the mass to move with any veloci- certain resistance, &c. A body as 2 a rety whatsoever. Our author himself seems to quires twice that force to be moved with the allow this towards the end of the same No. 2, same celerity, or it makes twice that resistwhen he is subdividing his celerities and ance; and so on.-This I think is not true; forces; for as in continuing the division to but that the body 2 a moved by the force lƒ eternity by his method of c, c, c, &c. (though the eye may judge otherwise of it) &c. you can never come to a fraction of ve- does really move with the same celerity as it locity that is equal to c, or no celerity at all; did when impelled by the same force; for 2 so dividing the force in the same manner, a is compounded of 1 a x 1a: and if each of you can never come to a fraction of force the 1 a's or each part of the compound were that will not produce an equal fraction of ce- made to move with 1 c (as they might be by lerity.-Where then is the mighty vis iner-2 f) then the whole would move with 2 c, and tie, and what is its strength; when the greatest assignable mass of matter will give to, or be moved by the least assignable force? Suppose two globes, equal to the sun and to one another, exactly equipoised in Jove's balance; suppose no friction in the centre of motion, in the beam or elsewhere; if a moscheto then were to light on one of them, would he not give motion to them both, causing one to descend and the other to rise? If it is objected, that the force of gravity helps one globe to descend, I answer, the same force opposes the other's rising: here is an equality that leaves the whole motion to be produced by the moscheto: without whom those globes would not be moved at all. What then does vis inertiæ do in this case? and what other effect could we expect if there were no such thing? Surely if it were any thing more than a phantom, there might be enough of it in such vast bodies, to annihilate so trifling a force by its opposition to motion?

Our author would have reasoned more clearly, I think, if, as he has used the letter a for a certain quantity of matter, and c for a certain quantity of celerity, he had employed one letter more, and put ƒ perhaps, for a certain quantity of force. This let us suppose to be done; and then as it is a maxim that the force of bodies in motion is equal to the quantity of matter multiplied by the celerity, (or f=c × a ;) and as the force received by and subsisting in matter, when it is put in motion, can never exceed the force given; so if f moves a with c, there must needs be required 2 f to move a with 2 c; for a moving with 2 c would have a force equal to 2 f, which it could not receive from 1ƒ; and this, not because there is such a thing as vis inertia, for the case would be the same if that had no existence; but because nothing can give more than it has, if 1 f can to 1 a give 1 c, which

But 1

not with 1 c, as our author supposes.
ƒ applied to 2 a, makes each a move with c;
and so the whole moves with 1 c; exactly the
same as 1 a was made to do by 1 ƒ before.
What is equal celerity but a measuring the
same space by moving bodies in the same
time?-Now if 1 a impelled by 1f measures
100 yards in a minute; and in 2 a impelled by
1f, each a measures 50 yards in a minute,
which added make 100; are not the celeri-
ties as the forces equal? and since force and
celerity in the same quantity of matter are
always in proportion to each other, why
should we, when the quantity of matter is
doubled, allow the force to continue unim-
paired, and yet suppose one half of the cele-
rity to be lost?-I wonder the more at our
author's mistake in this point, since in the
same number I find him observing: "We
may easily conceive that a body as 3 a, 4 c,
&c., would make 3 or 4 bodies equal to once
a, each of which would require once the first
force to be moved with the celerity c." If
then in 3 a, each a requires once the first
force ƒto be moved with the celerity, c, would
not each move with the force fand celerity
c; and consequently the whole be 3 a mov-
ing with 3 fand 3 c? After so distinct an ob-
servation, how could he miss of the conse-
quences, and imagine that 1 c and 3 c were the
same? Thus as our author's abatement of ce-
lerity in the case of 2 a moved by 1 f is ima-
ginary, so must be his additional resistance.-
And here again, I am at a loss to discover any
effect of the vis inertiæ.

In No. 6, he tells us, that all this is likewise certain when taken the contrary way, viz. from motion to rest; for the body a moving with a certain velocity, as c, requires a certain degree of force or resistance to stop that motion, &c." that is, in other words, equal force is necessary to destroy force. It may

be so. But how does this discover a vis iner- | panies it, have reconciled me to those convultie? Would not the effect be the same if there sions which all naturalists agree this globe has were no such thing? A force 1f strikes a body 1 a, and moves it with the celerity 1 c, i. e. with the force 1 f: it requires, even according to our author, only an opposing 1 f to stop it. But ought it not (if there were a vis inertia) to have not only the force 1 f, but an additional force equal to the force of vis inertiæ, that obstinate power by which a body endeavours with all its might to continue in its present state, whether of motion or rest? I say, ought there not to be an opposing force equal to the sum of these?-The truth however is, that there is no body, how large soever, moving with any velocity, how great soever, but may be stopped by any opposing force, how small soever, continually applied. At least all our modern philosophers agree to tell us so.

Let me turn the thing in what light I please, I cannot discover the vis inertia, nor any effect of it. It is allowed by all, that a body 1 a moving with a velocity 1 c, and a force 1 ƒ striking another body 1 a at rest, they will afterwards move on together, each with c and f; which, as I said before, is equal in the whole to 1 c and 1 f. If vis inertia, as in this case, neither abates the force nor the velocity of bodies, what does it, or how does it discover itself?

I imagine I may venture to conclude my observations on this piece, almost in the words of the author; that if the doctrines of the immateriality of the soul and the existence of God and of divine providence are demonstrable from no plainer principles, the deist [i. e. theist] has a desperate cause in hand. oppose my theist to his atheist, because I think they are diametrically opposite; and not near of kin, as Mr. Whitfield seems to suppose; where (in his journal) he tells us," Mr. B. was a deist, I had almost said an atheist ;" that is chalk, I had almost said charcoal.

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suffered. Had the different strata of clay,
gravel, marble, coals, lime-stone, sand, mine-
rals, &c. continued to lie level, one under the
other, as they may be supposed to have done
before those convulsions, we should have had
the use only of a few of the uppermost of the
strata, the others lying too deep and too diffi-
cult to be come at; but the shell of the earth
being broke, and the fragments thrown into
this oblique position, the disjointed ends of a
great number of strata of different kinds are
brought up to-day, and a great variety of use-
ful materials put into our power, which would
otherwise have remained eternally concealed
from us. So that what has been usually look-
ed upon as a ruin suffered by this part of the
universe, was, in reality, only a preparation,
or means of rendering the earth more fit for
use, more capable of being to mankind a con-
venient and comfortable habitation.
B. FRANKLIN.

To the Abbé Soulavie.*

Theory of the Earth.-Read in the American
Philosophical Society, November 21, 1788.

PASSY, September 22, 1782.

I RETURN the papers with some corrections. I did not find coal mines under the calcareous rock in Derbyshire. I only remarked, that at the lowest part of that rocky mountain which was in sight, they 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, it seemed a proof, that there had been a great boulversement 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 The din of the market* increases upon me; happen, if the earth were solid to the centre. and that, with frequent interruptions, has, II therefore imagined, that the internal parts find, made me say some things twice over; might be a fluid more dense, and of greater and, I suppose, forget some others I intended specific gravity than any of the solids we are to say. It has, however, one good effect, as acquainted with, which therefore might swim it obliges me to come to the relief of your pa- in or upon that fluid. Thus the surface of tience with B. FRANKLIN. the globe would be a shell, capable of being broken and disorded 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 Nowest 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,

To Dr. John Pringle.
On the different Strata of the Earth.
CRAVEN-STREET, Jan. 6, 1758.

I RETURN you Mr. Mitchell's paper on the strata of the earth with thanks. The reading of it, and perusal of the draft that accom

* Dr. Franklin lived in Market-street, on the North side, between 4th & 5th streets, on the east corner of an alley, where the first metal conductor still remains. †The paper of Mr. Mitchell, here referred to, was published afterwards in the Philosophical Transactions of London.

VOL. II.... 3 C

33

* Occasioned by his sending me some notes be had taken of what I had said to him in conversation on the Theory of the Earth. I wrote it to set him right in some point wherein he had mistaken my meaning. B. F.

and M. Amontons calculated, that its density | star, he migh govern his course by the com

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.

pass; that it was by the power of this gene-
ral magnetism this globe became a particular
magnet. In soft or hot iron the fluid of mag-
netism 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 po-
lar and equatorial diameters differing from each
other near ten leagues, it is easy to conceive,
in case some power should shift the axis gra-
dually, 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 re-
gions, and what a rising in the present polar
regions; so that vast tracts would be disco-

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 mat-vered, that now are under water, and others ters lighter than the central parts of that air covered, that are now dry, the water rising and immersed in it, would recede from the and sinking in the different extremes near centre, and rise till they arrived at that region five leagues. Such an operation as this posof the air which was of the same specific gra- sibly occasioned much of Europe, and among vity with themselves, where they would rest; the rest this mountain of Passy on which while other matter, mixed with the lighter live, and which is composed of limestone, air, would descend, and the two meeting rock and sea-shells, to be abandoned by the would form the shell of the first earth, leav- sea, and to change its ancient climate, which ing the upper atmosphere nearly clear. The seems to have been a hot one. The globe beoriginal movement of the parts towards their ing now become a perfect magnet, we are, common centre would naturally form a whirl perhaps, safe from any change of its axis.there; which would continue upon the turn-But we are still subject to the accidents on ing of the new-formed globe upon its axis, and the surface, which are occasioned by a wave the greatest diameter of the shell would be in the internal ponderous fluid; and such a in its equator. If by any accident afterwards wave is producible by the sudden violent exthe axis should be changed, the dense internal plosion you mention, happening from the juncfluid, by altering its form, must burst the shell tion of water and fire under the earth, which and throw all its substance into the confusion not only lifts the incumbent earth that is over in which we find it. I will not trouble you the explosion, but impressing with the same at present with my fancies concerning the force the fluid under it, creates a wave, that manner of forming the rest of our system. may run a thousand leagues, lifting, and thereSuperior beings smile at our theories, and at by shaking, successively, all the countries unour presumption in making them. I will just der which it passes. I know not, whether I mention, that your observations on the ferrugi- have expressed myself so clearly, as not to nous nature of the lava which is thrown out get out of your sight in these reveries. If from the depths of our volcanoes, gave me they occasion any new inquiries, and produce great pleasure. It has long been a supposition a better hypothesis, they will not be quite of mine, that the iron contained in the surface useless. You see I have given a loose to of the globe has made it capable of becoming imagination; but I approve much more your as it is, a great magnet; that the fluid of mag-method of philosophising, which proceeds upnetism perhaps exists in all space; so that on actual observation, makes a collection of there is a magnetical north and south of the facts, and concludes no farther than those universe, as well as of this globe, and that if facts will warrant. In my present circumit were possible for a man to fly from star to stances, that mode of studying the nature of

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P. S. I have heard, that chemists 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.

To David Rittenhouse.

New and curious Theory of Light and Heat.Read in the American Philosophical Society, November 20, 1788.

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 organized 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, organized or not, quitting easily in totality those not organized, 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?

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?

Perhaps, when this globe was first formed, | virtue of the masses of iron ore contained in and its original particles took their place at it, might not some ages pass before it had certain distances from the centre, in propor- magnetic polarity? tion 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 organized 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?

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 May it not have been from such consider-changing its poles, and thereby wrecking and ations that the ancient philosophers supposed a sphere of fire to exist above the air of our atmosphere? B. FRANKLIN.

To Mr. Bowdoin. Queries and Conjectures relating to Magnetism and the Theory of the Earth.--Read in the American Philosophical Society, January 15, 1790.

I RECEIVED your favours by Messrs. Gore, Milliard, 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?

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 interIs it likely that iron ore immediately ex- nal fluid globe be immediately sensible of a isted when this globe was first formed; or change in the situation of the earth's axis, may it not rather be supposed a gradual pro- alter its form, and thereby burst the shell, and duction of time? throw up parts of it above the rest? As if we If the earth is at present magnetical, in | would alter the position of the fluid contained

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