From Benjamin Franklin to Jean-Louis Giraud Soulavie, 22 September 1782
To Jean-Louis Giraud Soulavie4
Copy, signed:5 Historical Society of Pennsylvania; copies: American Philosophical Society (two), Indiana University
Passy. Sepr. 22d. 1782
Sir
I return the Papers with some corrections.6 I did not7 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, there were Oyster Shells mixed with the Stone; & 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, & 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 Center. I therefore imagined that the internal parts might be a fluid more dense, & 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 & 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 & Water could be contained in a strong glass Vessel, the Air would be seen to take the lowest place & the Water to float above & upon it; & as we know not yet the degree of Density to which Air may be compressed, & M. Amontons calculated, that its Density encreasing as it approached the Center in the same proportion as above the Surface it would at the depth of [blank in MS] Leagues be heavier than Gold,8 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 central fires:— Tho’ as you observe the sudden Rarefaction of Water coming into Contact with those fires, may be an Agent sufficiently strong for that purpose, when acting between the incumbent Earth & 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 & occupying a great Space they would as soon as the Almighty Fiat ordained Gravity or the mutual Attraction of certain Parts, & the mutual repulsion of other Parts to exist all move towards their common Center: That the Air being a fluid whose Parts repel each other, though drawn to the Common Center by their Gravity, would be densest towards the Center & rarer as more remote; consequently all Matter lighter than the central Parts of that Air, & immersed in it, would recede from the Center & rise till they arrived at the 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 & 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 Center would9 form a Whirl there; which would continue in the turning of the new formed Globe upon its Axis & 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 & 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 & at our presumption in making them. I will just mention that your observation 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 substance of the Globe has made it capable of becoming, as it is, a Great Magnet. That the Fluid of magnetism exists perhaps in all space; so that there is a Magnetical North & South of the Universe as well as of this Globe, & 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 a Magnet, it is drawn to one end of the Iron, made denser there & rarer at the other. While the Iron continues soft & 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 the present kept parallel to itself, & not liable to the changes it formerly suffered, which occasioned the Rupture of its Shell, the submersion & Emersions of its Lands & the confusions of its Seasons. The present Polar & equatorial Diameters differing from each other near ten Leagues. It is easy to conceive in case some Power should shift the Axis gradually, & place it in the present Equator, & make the New Equator pass through the present Poles, what a sinking of the Waters would happen in the present equatorial regions, & what a rising in the present polar Regions; so that vast tracts would be discovered that now are under Water, & others covered that now are dry, the Water rising & sinking in the different Extreams near five Leagues. Such an operation as this, possibly, occasioned much of Europe, & among the rest this Mountain of Passy on which I live, & which is composed of Limestone Rock & Seashells, to be abandoned by the Sea & to change its antient Climate, which seems to have been a hot One. The Globe being now become a permanent Magnet we are perhaps safe from any future 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; & such a Wave is produced by the sudden violent Explosion you mention happening from the Junction of Water & 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 & thereby shaking successively all the countries under which it passes.1 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 enquiries & produce a better Hypothesis they will not be quite useless. You see I have given a loose to the Imagination, but I approve much more your Method of philosophizing, which proceeds upon actual Observation, makes a collection of facts, & 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 & therefore I have permitted myself to wander a little in the wilds of fancy. With great Esteem I have the honor to be Sir &c,
B Franklin
PS. I have heard that Chemists can by their art decompose Stone & Wood, extracting a considerable Quantity of Water from the one & Air from the other. It seems natural to conclude from this that Water & Air were ingredients in the 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, & produce Heat or light, we do not create that Heat or light; we only decompose a Substance which received it originally as a part of its composition? Heat may thus be 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, & the whole when pressed together produced the Internal fire which still subsists.
[In Franklin’s hand:] Letter to Abbé Soulavie 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.
No 1
4. This letter was eventually published as “Conjectures concerning the formation of the Earth, &c. in a letter from Dr. B. Franklin, to the Abbé Soulavie”: APS Trans., III (1793), 1–5. BF gave it and several other pieces to the APS in 1788, after offering them first to the American Academy of Arts and Sciences in 1786 (BF to JW, Jan. 27, 1786, Yale University Library).
5. In the hand of Samuel Vaughan, Jr., and probably made in 1786 when he and BF were both in Philadelphia, and BF was organizing his papers. BF numbered the copy and wrote the explanatory note at the end; it is now in the William Smith Papers. The two copies at the APS are in the Benjamin Vaughan Papers; BFB wrote the first one, and Benjamin Vaughan copied BFB’s version. BF made one emendation to BFB’s copy (indicated in annotation below), and endorsed it, “Letter to M L’Abbé Soulavie, on some Parts of the Theory of the Earth.” Vaughan turned that endorsement into a title. The copy at Indiana University is among JW’s papers and is in the hand of L’Air de Lamotte. There is also a French translation by the abbé de La Roche at the Institut de France.
6. Soulavie had sent BF an account (now lost) of what he had understood BF to say about the earth’s formation during an earlier conversation about geology and politics. He hoped to insert BF’s views in vol. 5 of his Histoire naturelle de la France méridionale, which was already in press: XXXVII, 384–5; and see Soulavie’s answer to the present letter, Oct. 21. The publication of vol. 5 was delayed until 1784 and did not, in the end, include BF’s geological observations. Soulavie did mention them, however, in an account of their conversation which he published in 1801. The section of that published “conversation” that deals with geology, incorporating BF’s views as expressed in the present letter, is in XXXV, 356–7.
7. On the copy made by BFB, BF here inserted the phrase “as you suppose.” Benjamin Vaughan, copying BFB, followed suit. This insertion does not appear in the other copies or in the APS publication.
8. Guillaume Amontons (1663–1705) found that at 19 leagues air would equal gold in density: “Sur le nouveau thermometre de M. Amontons,” Histoire de l’Académie royale des sciences for 1703, pp. 7–8. The blank space in BF’s letter was preserved in all copies and in the APS publication. The abbé de La Roche, in his French translation (noted above), filled in the blank with the number 7.
9. All other versions have “naturally” here.
1. The translation by the abbé de La Roche added here the following sentence: “C’est du moins l’effet que m’ont dit avoir éprouvé des tremblemens de terres les personnes éclairées que j’ai consultées et qui se sont trouvées dans les cas de les observer Sur le continent de l’Europe et de l’amerique.” In the margin next to “les personnes” La Roche added “M. Olavides.” Pablo Antonio José de Olavide y Jáuregui (1725–1803), a Spanish statesman born in Peru, had witnessed the devastating earthquake of 1749 at Lima. He had been living in France since 1780. Javier Abués Villa et al., eds., Gran Enciclopedia de España (17 vols. to date, Zaragoza, 1990– ); Larousse.