in the progress of the experiment, be longer melting. They should therefore be kept so long in the wax, as to be all well and equally heated. Perhaps you may thus find the progress of heat in the silver quicker and greater. I think, also, that, if the hot oil in which you dipped the ends was not stagnant, but in motion, the experiment would be more complete, because the wire which quickest diminishes the heat of the oil next to it, finds soonest the difficulty of getting more heat from the oil farther distant, which depends on the nature of the oil as a conductor of heat, that which is already cooled interfering between the hotter oil and the wire. In reversing the experiment also, to try which of the metals cools fastest, I think the wires should be dipped in running cold water; for, when stagnant, the hot wires, by communicating heat to the water that is near them, will make it less capable of receiving more heat; and, as the metals which communicate their heat most freely and readily will soonest warm the water round them, the operation of such metals may therefore soonest stop; not because they naturally longer withhold their heat, but because the water near them is not in a state to receive it. I do not know that these hints are founded; I suggest them only as meriting a little consideration. Every one is surprised that the progress of the heat seems to have no connexion with the gravity or the levity of the metals.

B. FRANKLIN.

An Account of Toads found enclosed in Solid Stone.

Ar Passy, near Paris, April 6th, 1782, being with M. de Chaumont, viewing his quarry, he mentioned to me, that the workmen had found a living toad shut up in the stone. On questioning one of them, he told us, they had found four in different cells which had no communication; that they were very lively and active when set at liberty; that there was in each cell some loose, soft, yellowish earth, which appeared to be very moist. We asked, if he could show us the parts of the stone that formed the cells. He said, No; for they were thrown among the rest of what was dug out, and he knew not where to find them. We asked, if there appeared any opening by which the animal could enter. He said, No. We asked, if, in the course of his business as a laborer in quarries, he had often met with the like. He said, Never before. We asked, if he could show us the toads. He said, he had thrown two of them up on a higher part of the quarry, but knew not what became of the others.

He then came up to the place where he had thrown the two, and, finding them, he took them by the foot, and threw them up to us, upon the ground where we stood. One of them was quite dead, and appeared very lean; the other was plump and still living. The part of the rock where they were found, is at least fifteen feet below its surface, and is a kind of limestone. A part of it is filled with ancient seashells, and other marine substances. If these animals have remained in this confinement since the formation of the rock, they are probably some thousands of years old. We have put them in spirits of wine, to preserve their bodies a little longer. The

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.

B. FRANKLIN.*

*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.

"SIR,

"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.

READ AT A MEETING OF THE AMERICAN PHILOSOPHICAL SOCIETY, NOVEMBER 21st, 1788.

SIR,

Passy, 22 September, 1782.

I did

I return the papers with some corrections. 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, "JOHN PRINGLE."

* 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.-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