operation when the space of water to be crossed is considerable; there is a method in which a swimmer may pass to great distances with much facility, by means of a sail. This dis**covery I fortunately made by accident, and in the following manner. whatever resulting from it, and that at least On the Causes of Colds. March 10, 1773. When I was a boy I amused myself one day with flying a paper kite; and approaching the bank of a pond, which was near a mile broad, I tied the string to a stake, and the -I SHALL not attempt to explain why kite ascended to a very considerable height damp clothes occasion colds, rather than wet above the pond, while I was swimming. In a ones, because I doubt the fact; I imagine that e little time, being desirous of amusing myself neither the one nor the other contribute to with my kite, and enjoying at the same time this effect, and that the causes of colds are the pleasure of swimming, I returned; and totally independent of wet and even of cold. loosing from the stake the string with the lit- I propose writing a short paper on this subtle stick which was fastened to it, went again ject, the first moment of leisure I have at my into the water, where I found, that, lying on disposal. In the meantime I can only say, my back and holding the stick in my hands, I that having some suspicions that the common was drawn along the surface of the water in a notion, which attributes to cold the property very agreeable manner. Having then engaged of stopping the pores and obstructing perspianother boy to carry my clothes round the pond, ration, was ill-founded, I engaged a young to a place which I pointed out to him on the physician, who is making some experiments 3. other side, I began to cross the pond with my with Sanctorius's balance, to estimate the difkite, which carried me quite over without the ferent proportions of his perspiration, when least fatigue, and with the greatest pleasure remaining one hour quite naked, and another imaginable. I was only obliged occasionally warmly clothed. He pursued the experiment to halt a little in my course, and resist its pro- in this alternate manner for eight hours sucgress, when it appeared that, by following too cessively, and found his perspiration almost quick, I lowered the kite too much; by doing double during those hours in which he was which occasionally I made it rise again. I naked. B. FRANKLIN. have never since that time practised this singular mode of swimming, though I think it not impossible to cross in this manner from Dover to Calais. The packet-boat, however, is still preferable. B. FRANKLIN. To M. Dubourg. On the free Use of Air. LONDON, July 28, 1760. To Francis Hopkinson. PHILADELPHIA, 1748. ACCORDING to my promise, I send you in writing my observations on your book ;* you will be the better able to consider them; which I desire you to do at your leisure, and set me right where I am wrong. I stumble at the threshold of the building, and therefore have not read farther. The author's vis inertia essential to matter, upon which the whole work is founded, I have not been able to comprehend. And I do not think he demonstrates at all clearly (at least to me he does not) that there is really such a property in matter. -I GREATLY approve the epithet which you give, in your letter of the 8th of June, to the new method of treating the small-pox, which you call the tonic or bracing method; I will take occasion, from it, to mention a practice to which I have accustomed myself. You know the cold bath has long been in vogue here as a tonic; but the shock of the cold water has always appeared to me, generally speak ing, as too violent, and I have found it much more agreeable to my constitution to bathe in lerity be called c. another element, I mean cold air. With this view 1 rise almost every morning, and sit in my chamber without any clothes whatever, half an hour or an hour, according to the sea son, either reading or writing. This practice is not in the least painful, but, on the contrary, agreeable; and if I return to bed afterwards, before I dress myself, as sometimes happens, I make a supplement to my night's rest of one or two hours of the most pleasing sleep that can be imagined. I find no ill consequences He says, No. 2. "Let a given body or mass of matter be called a, and let any given ceThat celerity doubled, tripled, &c. or halved, thirded, &c. will be 2 C, 3 c, &c. or c, c, &c. respectively; also the body doubled tripled, or halved, thirded, will be 2 a, 3 a, or a, a, respectively." Thus far is clear.-But he adds, "Now to move the body a with the celerity c, requires a certain force to be impressed upon it; and to move it with a celerity as 2 c, requires twice that force to be impressed upon it, &c." Here * Baxter's Inquiry into the Nature of the Human Soul. is the same thing as giving it 1 ƒ; (i. e. if force applied to matter at rest, can put it in motion, and give it equal force) where then is vis inertia? If it existed at all in matter, should we not find the quantity of its resistance subtracted from the force given? the I suspect some mistake creeps in by the author's not distinguishing between a great force applied at once, or a small one continually applied to a mass of matter, in order to move it. I think it is generally allowed by the philosophers, and, for aught we know, is certainly true, that there is no mass of matter, how great In No. 4. our author goes on and says, 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 lf 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 la: 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 tic, 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=cx 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 1f; 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 not with 1 c, as our author supposes. But 1 f applied to 2 a, makes each a move with e; 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 1 f, each a measures 50 yards in a minute, which added make 100; are not the celerities 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 unimpaired, 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 ƒ and celerity c; and consequently the whole be 3 a moving with 3 fand 3 c? After so distinct an observation, how could he miss of the conse quences, and imagine that 1 cand 3c were the same? Thus as our author's abatement of celerity in the case of 2 a moved by 1f is imaginary, 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. tie? Would not the effect be the same if there 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 1f 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. But how does this discover a vis iner- | panies it, have reconciled me to those convulsions which all naturalists agree this globe has suffered. Had the different strata of clay, gravel, marble, coals, lime-stone, sand, minerals, &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 difficult 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 useful materials put into our power, which would otherwise have remained eternally concealed from us. So that what has been usually looked 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 convenient and comfortable habitation. 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 f striking another body I 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 inertiæ, 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. The din of the market* increases upon me; and that, with frequent interruptions, has, II find, made me say some things twice over; and, I suppose, forget some others I intended to say. It has, however, one good effect, as it obliges me to come to the relief of your patience with B. FRANKLIN. To Dr. John Pringle. B. FRANKLIN. To the Abbé Soulavie.* Theory of the Earth.-Read in the American 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 happen, if the earth were solid to the centre. 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 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 lowest place, and the water to float above and I RETURN you Mr. Mitchell's paper on the strata of the eartht with thanks. The reading of it, and perusal of the draft that accom-upon it; and as we know not yet the degree of density to which air may be compressed, * 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 3333 * Occasioned by his sending me some notes he 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 points 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. 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 observations on 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 pass; 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 resuining 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 passes. I know not, whether I have expressed myself so clearly, as not to get out of your sight in these reveries. If they occasion any new inquiries, 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 da the globe is out of my power, and therefore I | but does not extend to the making or creating have permitted myself to wander a little in 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 籍 P. S. I have heard, that chemists can by universe. We cannot destroy any part of it, their art decompose stone and wood, extract- or make addition to it; we can only separate **ing a considerable quantity of water from the it from that which confines it, and so set it at one, and air from the other. It seems natural liberty; as when we put wood in a situation to conclude from this, that water and air were to be burnt, or transfer it from one solid to aningredients in their original composition; for other, as when we make lime by burning men cannot make new matter of any kind.-stone, a part of the fire dislodged in the fuel In the same manner may we not suppose, that being left in the stone. May not this fluid, when we consume combustibles of all kinds, when at liberty, be capable of penetrating and and produce heat or light, we do not create entering into all bodies, organized or not, quitthat heat or light; but only decompose a sub-ting easily in totality those not organized, and stance, which received it originally as a part quitting easily in part those which are; the of its composition! Heat may be thus consi- part assumed and fixed remaining till the body dered 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 Beat.- 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; 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? |