“The variation of the compass can only be accounted for by supposing the central parts of the earth to consist of a fluid mass, and that part of this fluid is iron, which requiring a greater degree of heat to bring it into fusion than glass or other metals, remains a solid ore. The vis inertiæ of this fluid mass with the iron in it occasions it to perform fewer revolutions than the crust of solid earth over it; and thus it is gradually left behind, and the place where the floating iron resides, is pointed to by the direct or retrograde motion of the magnetic needle.”
Of bellows made of Franklin’s air.
In the first paper of the third volume of Transactions of the American Philosophical Society, you will find certain “Conjectures concerning the formation of the earth,” &c. in a letter from Dr B. Franklin, to the abbe Soulavie; which we would prescribe as tonics to Hutton’s system. The American sage informs us, that in the course of some observations in Derbyshire, in England, he “imagined that the internal part (of the earth) 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 disordered by any 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;[D] 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 rarefication 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 other parts to exist, all move towards 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 part 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.[E] The original movement of the parts towards their common centre, would naturally form a whirl there, which would continue in 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,” [viz. by the impinging of a Buffon’s comet’s tail or the delivery of a Darwin’s moon] “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!” There’s an air gun for your worships!
Now, if we did not possess a particular partiality for the sage who formed this system, we should probably break up his Eolian cave, even at the risk of creating half a hundred hurricanes. For should we open a vent as large as a needle’s point into this magazine of compressed air, you would instantly be assailed by “another guess whistling”[F] than was the tempest tost Trojan fleet when
Una Eurusque Notusque ruunt creberque procellis.
Destroy good doctor Burnet’s crust.
We should be able to make much more rapid progress in our sublime flights of poetry, were we not under the necessity of dismounting from our Pegasus every ten paces, in order to give your worships a heist, and thus enable your ponderosities, like Mr Pope’s “slugs,” to keep up with us. It is a thousand to one if any one of your college has ever heard of Dr Burnet, of earth-manufacturing memory. But it is absolutely necessary that you should know something of Dr Burnet’s theory before you can comprehend the stanza to which this note has reference. You will, therefore, shut up this, my volume, and per fas aut nefas obtain possession of Dr Burnet’s theory of the earth’s formation; and when you have diligently drudged through that treatise, we will again take you in tow, and permit you to accompany us, but non passibus equis, till our muse salutes you with procul! O procul! &c.