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workmen have promised to call us, if they meet with any more, that we may examine their situation. Before a suitable bottle could be found to receive them, that which was living when we first had them appeared to be quite dead and motionless; but being in the bottle, and the spirits poured over them, he flounced about in it very vigorously for two or three minutes, and then expired.

It is observed, that animals who perspire but little, can live long without food; such as tortoises, whose flesh is covered with a thick shell, and snakes, who are covered with scales, which are of so close a substance as scarcely to admit the passage of perspirable matter through them. Animals that have open pores all over the surface of their bodies, and live in air which takes off continually the perspirable part of their substance, naturally require a continual supply of food to maintain their bulk. Toads shut up in solid stone, which prevents their losing any thing of their substance, may perhaps for that reason need no supply; and being guarded against all accidents, and all the inclemencies of the air and changes of the seasons, are, it seems, subject to no diseases, and become as it were immortal.


*The following copy of a letter from Sir John Pringle to Mr. A. Small, was annexed to the above account, in Dr. Franklin's papers. W. T. F.

"Minorca, 25 April, 1780.


"Last year I had the honor to inform you, that two of those large moths called Muskitoe Hawks, which appear about September, and disappear about the beginning of December, lived seventy-one days after I had cut their heads off with a pair of scissors.

"The last autumn, I made the same experiment upon several, keeping them under separate glasses, in a closet, where there was no fire. The most of them lived different periods, from three, to sixty and seventy days. Those which exceeded that number of days were four, viz. one from the 30th of October to the 21st of January, eighty-three days; one from the


On the Theory of the Earth.


Passy, 22 September, 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, 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

12th of December to the 21st of April, one hundred and thirty-one days; and one from the 24th of October to the 15th of April, one hundred and seventy-four days. As they are very active, and covered with a sort of plumage, which makes it difficult to cut their heads off, without bruising or otherwise injuring the body, I imagine that may partly be the reason of their living different periods; and if, after the operation, any glutinous liquor proceeded from the body, that moth would die soon.

"I put several under glasses, without cutting off their heads, none of which lived many days.

"I am, Sir, with great esteem, your most obedient and most humble servant,


* 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 t to set him right in some points wherein he had mistaken my meaning.-Note by the Author.

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 with 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 seashells, 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

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